#I was tempted to also add their indoor design in this post (because yes- I also made some indoor designs >:3)
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from James Dole Gadgets News https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from Computer And Technology https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
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Let's just ignore the fact more than six months have passed since I last published a post on this site. Let's also not talk about the numerous post ideas I have listed in my notebook that haven't seen the light of day. Let's instead focus on how we came up with the design for this extension of ours (which, despite six months later is still three roof sheets short of being watertight from above! It's been... well it was all good until last month when the rain didn't stop and we had no roof. But that is a story for another day... Not six months away though, promise!)
So. When we were house hunting four years ago we had a few musts: it needed to be a fixer-upper because we wanted to make our own stamp on it. Location was important - we wanted to be close to the water. It had to have good light, good structural bones, a decent yard and the potential for us to add to it. We found the ugliest house in the best street with water views and snapped it up. The good thing about it being an ugly house was there was no history or architectural details which we had to work around which is often the case with old houses. This was fibro. It had plain walls, plain windows, plain cornices, plain everything. It was essentially a blank canvas (and I hate using that term, but it's true). Our last home had pretty cornices, timber windows and a real cottage-y feel to it we tried to keep while modernising it. Our first house was a historical semi we didn't dare touch aside from paint in tones true to its style. This house had nothing really. It gave us freedom to do what we wanted without feeling guilty about veering away from its "style" or stripping it of character. I believe in working with what you have and if it had any redeeming features, we'd definitely have worked with them in the design process. As it happened, we ended up creating the story of our house once work started - we recycled parts of the old roof into stair treads, changed the floor direction in the extension and kept a few original parts like the old knocker and house numbers. We have piles of hardwood from the roof that will become a bar top and library shelves. We reused the huge beams as heads above doorways and windows, moved some windows around and recycled doors. It's nice to have a kind-of-cool answer for the "why is that like that..." questions that might come.
But before we even got to creating a story, we had to create a plan. And while it's tempting to look at magazines and Pinterest and blogs and imagine yourself in that space, there are so many more factors to consider aside from loving something because it looks pretty. Captain Obvious, right? Well yes and no because despite all my constant writing about this stuff, it's easy to get swept away imagining something when the reality is likely to be very different. And know that it's not just a matter of things being different due to your tastes or location, but it's to the rules of YOUR property - and they might be different to your immediate neighbour's. It's the way you live your life. It's your actual home's ability to handle the changes you wish to make. It's your budget. And weather patterns. It's your personal needs and those of every person who lives there. The list of things that can affect your home's design is endless, so by all means look to others for inspiration, but be sure to design the best space for you and your family, taking into consideration all the musts/have-tos and can'ts along the way. After a few harsh realities from Steve (who rolled his eyes every time I showed him an all-white Swedish space and explained "something like this!"), I wondered how close to the mark we would get in terms of creating a home perfect for us. While we've not finished or been able to use our space completely, so far, I can't see much I'd change if I had free reign. Which makes me think the long, long design path was the right road to take. If you're looking at taking yourself on a similar renovation journey, here are a few things we learnt along the way.
Resist the urge to get renovating immediately
Any magazine article on renovating will tell you to live in your space before you do anything major to it. There is a good reason for this - because it helps you make better decisions. If you can do a full year, do it - because honestly, your home is so different throughout the seasons and you want to ensure you know it back to front. The light falls differently in winter to summer - we discovered the afternoon sun bounces off the verandah of the house across the street from us and rebounds into our bedroom in summer and lights up the south side of the home in winter. We know the afternoon sun is unbearable in summer at the back of our house (which faces West) but that the sea breeze cools things down most days too. We know how the yard floods and where the shade falls for prime planting. We've worked out where we have mould problems, where we like to dump our wallets and keys, how we don't walk down the driveway but across the middle of the lawn to the front door, which way the weather usually comes from and where the rain affects us most. Putting up with all the annoyances that come with an unrenovated house is worthwhile because you work out what annoys you, what you like, how you live, what you need to make living better - knowing all these things is essential for good design.
Create a wishlist
For us, we needed more space - we had a tiny three-bedroom, one-bathroom home. It had a living room, kitchen/dining and that was it. All up, it was 80sqm. We weren't after a huge house, but with four kids, we definitely needed more space! We renovated the bathroom and kitchen spaces with an extension in mind - we decided we could just extend from the back out so worked out a way to do just that so whenever the time came, the existing house shouldn't require much work. And then we planned and planned. We worked out what we wanted exactly: some kind of loft space, raked ceilings, two living spaces and a fireplace. We wanted at least four bedrooms, but five would be better so everyone could have their own room if they wished (I am now DYING for them to all be in their own rooms because I'm over the bed-swapping, whinging, kicking and meltdowns over who gets to stay up later and who doesn't...). I wanted lots of storage because the house had none. So we incorporated a dedicated storeroom into the plans. It turned out that Steve changed careers while waiting for council approval and so the storeroom has been renamed his workshop for all his tools. It will be the world's tiniest workshop but still! Luckily I still had large storage areas planned for the roof - having a high-pitched roof means the unusable areas can be walled off and used to store alllll sorts of things!
Get drawing
I've been a lover of floorpans forever! I'd draw my dream homes all the time complete with indoor pools, ballrooms, sweeping staircases and libraries. Being able to draw up a more realistic one for my family that we would actually build was so exciting! Several variations were drawn up - the first was turning one of the bedrooms into a staircase and adding a whole second storey to take advantage of the water views. Then I thought maybe not the whole hog and just a really high-pitched roof so we can have an attic bedroom. Another version had a master bedroom at the back next to second living space. Another kept our master where it was but stole the bedroom next to it for an ensuite and wardrobe and added two smaller rooms to the back. Yet another plan extended to the side of the house over the driveway. But I kept coming back to the attic idea - why couldn't we just make one big room out the back with a staircase up to a loft bedroom in a new roof? Sounded pretty easy to me, so I called in the draftsman...
Call in the experts
The thing with major renovations is this: there are SO MANY DIFFERENT ANNOYING RULES AND ASPECTS TO THE PROCESS. And you don't really know about any of them until you're at that stage. First up for us was the biggest bummer of all: we had to do a full development application for council. Many renovations and extensions won't require this - you can go through a private certifier and they can have your plans approved within a few weeks. But if you live in a flood or bushfire zone, you most likely won't be that lucky. We live in a flood zone and so straight up we had bonus conditions - the biggest being we had to raise the floor height by 60cm. This meant the nice walk-straight-out-of-your-living-room-onto-your-deck-onto-the-grass moments and easy view of the kids playing in the yard from anywhere in one side of your home wasn't going to happen. It would be about a metre or so off the actual ground. Having to step up the extension means a split level to the ground floor, which means extra materials in height (more bricks for footings/longer pieces of wood) extra precautions in stabilising the building and a more difficult build as it's higher off the ground (we had to lay a subfloor so the builders didn't just rely on standing on bearers and joists - this was an extra couple of thousand dollars immediately). The huge pitched ceiling I wanted with a bedroom in it? Couldn't quite do as I wanted - did you know habitable rooms (living/bedroom) require your ceiling height to be at a certain height (for memory it is 1.8m but I could be wrong there) for 2/3 of the volume of the room? We wanted the angled ceiling to just hit the floor, so in the end, knee walls had to be built to decrease the size of the room so our master bedroom won't quite be as we imagined it at first, but the library can be. There are also height restrictions (we just snuck in for how high our house can be), light-to-dark ratios through use of windows and doors, shading requirements (we need little awnings on our east-facing bedroom to shade them) and so. many. other. annoying. things. The draftsman/architect/builder who designs knows these tricky little things and will outline your options. In the end, our draftsman discovered if we submitted the second story as an "attic bedroom" rather than a second storey, we had a little more freedom with our plans. One thing I suggest is to give your draftsman/builder/architect a ball park figure of what you want to spend - underestimate it, though. Because if you give them no budget to work to, they will design just design to all your whims and you might end up with a house you actually can't afford to build! And never feel you have to do EVERYTHING all at once. It is a good idea to design your home and submit everything in one application with a view to doing it in stages as budget/time/circumstances allow. We never planned to complete our extension in one hit. We wanted to do it in two to three stages with our master bedroom and ensuite being the last thing. If you have plans to put in a pool or garage or separate studio down the track, consider doing it all as one DA and get the approval now. It will save you in extra drafting and application fees later on.
Draftsman vs architect vs builder vs carpenter Depending on the scale of your works you might not need a draftsman or architect. Many builders are able to draw up and submit plans on your behalf and if it's less complicated works to a place that doesn't change the footprint of your home, a carpenter might be all you need. We knew we needed plans drawn up but as we had a good idea of what we wanted, we knew a draftsman was all we needed. If you're stuck for ideas about what you want, I'd still start with a builder who can at least point you in the right direction of an architect if they believe one is required.
Make all your changes at this stage
Every time I got a draft plan from the draftsman I printed it out and got out my trusty red pen for changes - because there were always changes. I lived and breathed these plans - even dreamt about them sometimes! But that is the good thing about drafting plans - they are drafts and can be changed. And you should change them at the planning stage because it will cost you a lot more time, effort, money, patience and possibly relationships if you change them once the build begins! For me, I'd use the printouts to just see what it might look like if I moved the wall a little more this way. Or if I moved the door layout or added an extra room. Always sit on the current draft for a while and get a feel for what it might be like. Measure things out - I would use string and mark up the walls/doors/windows on the grass so I could physically see the floorplan in the right scale. Get a feel for the space in terms of size and look for things like views from windows and doors, door swings and potential furniture placement. There is often a little wiggle room for small changes once construction begins such as window size and placement, but nothing too drastic, so get it right now. We took our time with our plans - probably waaaay too long but there were a fair few delays on both sides of the process and in the end, we're glad there was a wait because we love our plans. We were also lucky in that our draftsman had a fixed price so it didn't matter how many changes we made, our $3000-odd fee for the measuring/drafting/submitting didn't budge. Spoiler alert: the engineering fees were a surprise $5000 we weren't expecting!
Turn negatives into positives
There are going to be restrictions but it's what you do with them... We had to raise our floor level which brought a few headaches for the builders and extra costs for us, but we started to see the advantages of having this split level. For one, it broke up the extra-long space and created two distinct living areas. It allows us to see the water views from the back room and has created a large under-house space where we will able to store our water tanks, excess building materials, kids bikes and surfboards etc. The fact we have to apply builder's bracing (which is essentially thin plywood sheets made from hardwood at $35 a sheet) to all of our existing interior walls killed me (and here I was thinking we wouldn't have to touch the existing house too much!) but it meant we were able to insulate them as well, meaning the bedrooms on either side of the bathroom are now a little more soundproof. It also got rid of the wallpaper that had been painted over and often bubbled up during wet periods and means our Gyprock walls will be nice and straight and new. The engineer's obsession with bracing, particularly expensive materials and extra strengthening requirements means our house is the strongest, well-built thing in town. It's not going anywhere!
Be realistic with your choices
Sometimes I would look at our plans and wish for larger expanses of glass by way of bifold doors from the family room onto the back deck. And then I remembered the heat in the middle of summer. And the bugs. And the sand and crap that would fall in the rails of the bifolds. And that I love French doors more... We went against the norm because it doesn't work for us. Realistically we knew we needed a decent size door opening but also windows on either side of them that could be open all night long if we wanted for safe, mozzie-free breezes and airflow. We knew as much as a big deck sounds great in theory, it would encroach too much into the backyard, which was more important. And we're not big entertainers anyway. We know pretty pendant lights are going to have to take a backseat to ceiling fans. And timber windows or louvres everywhere were just going to eat too much into the budget. Getting the right mix of practicality and aesthetics is hard and if you really want to live in a place, aesthetics will most of the time lose out to practicalities in a battle of the wits. Like my whitewashed floors. I love them to bits but we're going with a mid-range natural colour for floorboards because we're a rough and tumble family and that's the best colour to mask wear and tear and the inevitable dirt that comes with living with children. (Though Steve is still A-OK with my painting our eventual master bedroom floor pure white. It will have to be a no-shoe zone!) Think honestly about how you live, what your budget is and what is important to you and plan your home around them.
Expect delays and to pay a lot upfront
Dear God did we have delays... The whole process has had delays! And they will happen at one stage or another. For us it was just getting the plans right, then not pushing the draftsman to get them back to us as quickly as we should have. Then it was council approving our plans (after a couple of months) but not noticing we had asked for a one-metre extension to the existing house (four square metres in total) at the existing floor height to give the dining room a little more space before the floor level rose. So it was back to council for another six or so weeks as they had to start all over again. Then it was a matter of organising a certifier who couldn't give you a construction certificate to start works until you had waded through their list of things: engineer's report, home builder's course etc. In the end we forked out close to around the $15,000 mark before we even bought any materials or began labour. Here are some approximate figures for you because I honestly can't recall exact amounts and I am too lazy to sift through my disorganised paperwork to find them (sorry!)
Draftsman: $3300
Engineer: $5000
Council fees: $2000
Certifier: $3000
Surveyor: $200
Home owner/builder course and white card: $250
Long-service builder's levy: $500
In short, an architect told me when I wrote the Real Living Renovations magazine to never sign up and start building if all you have is the dollars the builder quoted you. Because it will ALWAYS cost you more, somewhere along the line. And it's usually before the builder even begins!
I hope this was somewhat helpful. Because frankly I haven't typed this much in a while and my fingers hurt (Kidding. I still write a fair bit; just not here!). If you're about to renovate, you can track down a copy of the reno magazine here or at your newsagent if they still have them in stock. Otherwise I did find a lot of what I wrote has been uploaded to the Homes to Love website. It's not everything, but it's a fair bit. I've linked to a few of the sections below.
Guide to hiring an expert
Choosing the right team
Researching and shopping
Surviving the construction stage
8 steps to a well-designed home
Kitchen design
Bathroom renovation
The owner/builder: what you need to know
The power of paint
Spotting the warning signs
Where your money goes
Renovating sourcebook
And for more of my Reno Files posts...
{The reno files} A real-life renovation guide: introduction
Our house plans: spending big to live small(ish)
A very exciting renovation update
A real, hopefully helpful and honest guide to renovating your bathroom
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Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
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Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from Computer And Technology https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
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Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from James Dole Gadgets News https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from James Dole Gadgets News https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
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Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from Computer And Technology https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from Computer And Technology https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
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Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from Computer And Technology https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
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Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from James Dole Gadgets News https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from James Dole Gadgets News https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
Text
Seven Rules for Accurate Site Surveys
The process of gathering appropriate and accurate data during site surveys is as simple as following a few easy rules. Break the rules, however, and you could end up with totally useless – but colorful – Heat Maps that have no value to your organization. These rules have been gleaned through hundreds of site surveys and through teaching over hundreds networking professionals how to use Site Survey products.
Rule 1 – Calibrate Your Drawing Properly
Setting the underlying ‘grid’ is critical. If you don’t accurately calibrate the drawing to reflect the reality of the actual building, with the drawing on your screen – all your data in your site surveys will be virtually worthless. This is #1 in the list because it is the most important step, and you should always do it correctly as soon as you open a new project.
Do not use a doorway as your ‘baseline’ to calibrate from. Use a longer dimension, as long as you can measure. I use a Laser measuring device that works out to 50m or so. Measuring wheels, long tape measures, laser, or sonar all work; just try to find the longest edge. You only need to have one dimension to accurately calibrate a drawing that comes to you with the correct aspect ratio.
Better yet, have the CAD folks drop a Dimension Line underneath the actual building on the drawing to give you an even more accurate line to calibrate against.
Note: While we’re on the subject of the drawing, simplify your drawings as much as possible, using only black and white. ‘Flatten’ the drawing down to just the simple floor plan, no need for furniture, plants, where the jacks are located. Just simple black on white walls in your drawing is best
Rule 2 – Set the Channel Scan to the Correct Frequencies
Scan ONLY the channels you want, and don’t scan the channels you don’t want. This sounds simple… but making a mistake here can cost you greatly in the accuracy of the post survey data. If you ‘accidentally’ set it to scan ALL channels (over 200 are available to scan) – even at only 250 ms each (1/4 second) the system will nearly a minute of time to return back to the starting channel. (and you can walk quite a long way in a minute!)
I recommend setting the scan channels to the 11 (or 13) base 2.4 GHz channels and the 5 GHz channels for your regulatory domain (in the US this can be the 4 Indoor Only, plus the 4 Indoor or outdoor channels) and do a passive survey of the outside perimeter of your building first.
This will give you a nice capture of your neighbors, as well as your ‘leaking’ RF. But better yet – it will give you a nice set of channels to concentrate on when moving indoors to do the real site surveys.
Perhaps even do two survey walks, one for 2.4 GHz and one for 5 GHz channels. That, or watch the bottom left corner of your survey screen and don’t move to the next data capture point until the channel scan marker returns back to ‘1’.
Scan what you want, and don’t scan what you don’t want!
Rule 3 – Set Your Guess Range Properly
This goes by the more professional term ‘Signal Propagation Assessment’ – but it basically means how far do you want your application to ‘guess’ (Interpolate) in between your captured data points when conducting site surveys.
Really accurate site surveys would set this down to one meter. But the problem there would be that you’d have to go and click on every single meter of space in your building. Accurate yes, but practical, no.
Or the opposite, go to the center of your building and take a single data snapshot… then set the Guess Range to 50 meters… This one is easy and quick, but not accurate at all.
Reality is somewhere in between. Most survey applications have a couple of pre-defined options for you. You do not have to use these pre-defined Signal Propagation Assessment (SPA) numbers. Use what you think appropriate for your site; the smaller the better. It will force you to take more data points and thus get more accuracy.
For most indoor buildings, I like about a 5m Signal Propagation Assessment value.
Rule 4 – Set Appropriate ‘Snap Rate’ For Your Situation
The automatic snap rate is based on a time. You set the number of seconds when your application will take an extra ‘snapshot’ of your RF information during your site surveys. Too fast and you’ll get ‘blue lines’ with too much information and slow down your processing. Too few and your snaps will be too spread out. (Think of Goldilocks… just right…)
If you are doing Manual (red-dot-only) site surveys – be sure to take a snapshot no further than what your SPA is set to. So if you set your ‘Guess Range’ or SPA at 5m, you must take a snapshot (click) at least every 5m.
Rule 5 – Capture on Both Sides of What You Care About
No ‘One Way Guesses’. This happens when you don’t capture on both sides of what you care about. If you take one data capture point on the inside perimeter of your building, and don’t also take one on the outside, then your survey application won’t know anything about the ‘thickness’ (in RF Attenuation) of the exterior wall. It ‘learns’ this by having data captures on both sides of the wall.
If you don’t care about the RF leaking outside, then this is fine. But if you do care about some area, whether it is inside or outside, you must do data captures on both sides.
Thus another corollary to this rule – Capture Outside In, Not Inside Out. Capture on the perimeters of the rooms you want to prove coverage – not one single shot from the center of each room.
One additional part to this rule; If you have ‘special’ places you need to be real sure about in your site surveys – then take extra data captures at those locations, ie. CEO’s desk, Board Room, etc.
Rule 6 – Click Accurately
You don’t actually walk through walls, walk on water, or fly when you are doing site surveys – don’t have your data look like you did or your credibility will be shot.
Prepare your walking paths in advance. You might even put little numbers on your drawing before you import it with the locations where you want to click (capture data) – and then you’ll just have to play ‘connect the dots’ with your feet later during the survey.
The old adage, Fail to Plan means Plan to Fail… holds true in this respect. I’ve seen many people who get lost, or get stuck down the end of a hallway and don’t seem to know what to do with the Survey, or where to go next. Preparation is key on this point.
If you can’t easily find yourself on the floor plan – it is a skill that can be practiced you know – then work on it until you are comfortable moving around in three-dimensional space.
When you are doing an AirMagnet Survey ‘manual’ survey, with red dots only, the dots are connected with dashed lines. These dashed lines, without blue dots, can go through walls, walk on water, and fly… it’s the autosnap blue dots we worry about.
Note: Here’s a trick to use while doing a survey. While standing still at the end of one data capture point, place your mouse cursor at the next place you plan on stopping, then start walking. When you arrive at the designated point, you only need to ‘click’ and the data point is collected right under where the cursor was waiting.
Anytime you can see a specific marking on a blueprint or floor plan, add a click for accuracy. Of course, you could walk the entire hall and your survey application would place all the data points as soon as you finished the length of the hall. But accuracy improves as you have accurate intermediate click points.
If you don’t go to all the locations and click accurately, you’ll be tempted to increase your SPA to ‘fill in’ the missing data points. (no one likes to see white spots on their heat maps).
Rule 7 – Always, Always Do A Passive Survey
You might have a reason to also do an Active Survey, (see Passive vs. Active Surveys article) but you ALWAYS must do a Passive Survey on the entire building you care about. I’d also recommend doing a Passive Survey on the exterior of the building as well.
A Passive Survey can give you information on your neighbors, others, and all of your own devices.
This is especially important for determining RF interference. If you don’t have neighbor information in your Active Survey, you can easily miss the interference on specific frequencies. Additionally, this can show you where your ‘collision domains’ are.
In addition to these rules that pertain to Passive Surveys, Active Surveys have some rules of their own…
Additional Rules for Active Site Surveys
Capture Data from ALL Access Points
It is quite easy to do an active survey and only get data on a subset of your Access Points. You can merge this with a Passive Survey data set and end up with what looks like an accurate survey, but it is NOT. You need to have ALL Access Points included in your Active Survey for accurate representation of your RF WLAN environment.
Capture To The Edge
When capturing Active Survey data from an Access Point, it is easy to not go to the edge of the coverage area… it’s so far to walk – so we might stop as soon as we can see the coverage meets some design goal, like -65dBm. But this is where the failure lies. The easiest requirement to design for a WLAN is RF Coverage, but it is only the first of many requirements (see False God of dB article). The hard thing to deal with is the interference, and you’ll only learn about this if you capture data to the edge of each Access Point’s coverage area. (yes, I know this is hard and expensive to do!)
Do NOT Set Roaming To Be Too Aggressive
I understand you may have the great power to over-ride the WLAN NIC’s roaming decision process with your survey application’s roaming options feature. This makes surveying much faster and easier. Don’t succumb to the temptation! If you set the Roaming Option to only connect at 54, 48, and 36 data rates, then your data will only show 54, 48, and 36 data rates. Since you didn’t capture the other data rate information, your report won’t show it to you.
In reality, your client cards will roam according to their own algorithms and will downgrade to whatever data rates are supported in the Access Points.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
And another adage that should always be remembered with respect to wireless LANs – just because you can, doesn’t mean that you should.
De-Skew Data In Sticky Situations
Sometimes when taking an Active Survey the data gets a bit ‘skewed’ in the direction of travel: away from the access points. If this is the case you’ll need to do two Active Surveys for each access point, one clock-wise and one counter-clockwise and then merge those together to ‘de-skew’ the stickiness.
Merge All Actives Before Merging With Passive
Just like it says.
If You Don’t Do Active Surveys Right – Don’t Do Active Surveys At All
If you do Active Surveys wrong, you’ll end up with a less-accurate and ‘worse’ data set than not doing any Actives at all.
Conclusions
Obey these rules for accurate site surveys or else… Or else the data you capture will be suspect at best, and totally useless at worst.
Also – don’t let your sub-contractors break the rules or ‘cheat’ on you either. Check out the How to ‘Cheat’ Using Survey – Don’t be a Victim article.
Additional Articles for Supporting WLAN Site Surveys
– How to ‘Cheat’ On A Survey – Don’t be a Victim
– The Fallacy of Channel Overlap
– Want, Don’t Want, Don’t Care – Meeting Design Specs
– The False God of dB
The post Seven Rules for Accurate Site Surveys appeared first on Wireless LAN Professionals.
from https://www.wlanpros.com/resources/seven-rules-accurate-site-surveys/
0 notes
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