7 Lessons Learned when doing Wireless Site Surveys

1 Have a checklist ready

You need to be able to answer the following before starting any survey:

  • Is the survey for voice, data, location etc.?
  • Frequency bands to be used: 2.4GHz or 5GHz?
  • Will it be an active or passive survey?
  • What type of client devices would be used?
  • What type of facility is it (warehousing, office environment, outdoor or a combination)?
  • Is it multi or single floor layout?
  • Remember to get those scaled floor plans.
  • Remember to ask about high density or client count in specific areas.
  • Do they need redundancy of their Access Points? If one AP goes down will they still have the required coverage.
  • What is the required Receiver Signal Strength Indicator (RSSI)?
  • What is the required Signal-to-Noise (SNR)?
  • What would the transmit (Tx) power be of the client devices?

 

2 Plan your survey

Make sure you do an initial walkthrough that would help you identify access to all areas, define which areas need to be surveyed (restrooms and emergency staircases might be out-of-scope), anticipate areas that might be more difficult than others to survey (a busy high ceiling reception area compared to an open office area) and so on.

This would also be a good time to identify the high-availability and high-density areas discussed before. You would also have to note any power needs and consider cabling and mounting positions for your Access Point during the survey.

After all this, it is now time to prepare your Airmagnet Survey or Ekahau survey according to the checklist and walkthrough that was done.

 

3 Calibrate your map

Make sure you use the calibration tool in your site survey software, you should be able to draw a line between two points and as long as you then provide the correct distance between those two points it should rescale the map according to that distance. The longer the distance between the two points the more accurate you will be when calibrating your map.

Data gathered from a map not calibrated or calibrated incorrectly will provide inaccurate results and you won’t be able to correct the calibration. You will have to start over.

If it doesn’t look right it probably isn’t scaled correctly. Look at stretched or skewed maps or when one AP shows coverage over a large area might be an indication of an invalid map not properly scaled.

 

4 Signal Propagation

When you start a new survey there should be an opportunity to set the signal propagation. This allows the site survey application to predict signal propagation between data points. If this value is too high, the results render inaccurately and might show acceptable signal levels in areas where there is insufficient coverage.

Your survey application might have a measurement set for office environments, hospitals, warehouses or outdoors but when I’m doing an indoor area like a hospital, meeting rooms and office space I usually set my signal propagation to 3 meters, warehouse to 5 meters and outdoors could be slightly higher.

When your signal strength after a survey shows coverage far from the path you walked it might be an indicator that you made a mistake when setting your signal propagation.

 

5 Channel Scanning

It is recommended that you scan only the channels that are in use by the wireless infrastructure. You might receive inaccurate readings if you walk too fast between data points and do not give the adapter enough time to complete the entire scan list. So be careful not to scan too many channels as it does take time to complete the entire scan list while surveying. Also, if you are looking for Rogue AP’s you will need to scan all channels before you can be 100% sure you picked up all devices.

 

6 Walking Paths

When you receive a survey make sure to check the walking paths of the surveys completed. Check that the person that did the survey didn’t walk through areas that was impossible to walk through, like a wall. That is an indication that your results might be wrong.

Also make sure your single AP survey is complete meaning the person that did the survey went beyond the coverage cell edge that was decided on before the survey started.

 

7 Post-validation survey checklist

Here are some of the major targets to look out for when a survey is complete:

  • Do we have sufficient coverage? If it was decided to get a minimum signal strength of -67 dBm then ensure that is what was achieved.
  • Is the channel overlap adequate? If you were looking at a 20% overlap between coverage cells then check that it was achieved.
  • Signal-to-noise ratio. As per coverage and channel overlap ensure you achieved measures set when planning your survey
  • There might be a few other measures to check such as data rates, noise floor, bleed through, rogue devices and interferers.

 

Reference

Cisco Site Survey Guidelines for WLAN Deployment

 

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7 Lessons Learned when doing Wireless Site Surveys

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