Wireless Site Survey

Tutorial by: NightShade1

 

What is a Wireless Site  Survey?

A really fast definition and  straigh to the point would be  the design and planning of a Wireless Network

 

Types of Wireless Site Survey

 

  1. Passive Site Survey
  2. Active Site Survey
  3. Predictive Site Survey

 

Passive Site Survey

What is?
This is the most usual type of site survey, or at least is what i think.  Its done on site, and what you do its collect data of the radio frequency enviroment,  you dont need to connect to any AP in this type of Site Survey

What type of Data you can collect with it?

  • Signal Level
  • How much interference is on the Area
  • How many APs
  • Placement of APs
  • Requirements such as BW per Device
  • Etc

Example of Tools Used

 

  • Wifi Testers for example a Fluke AirChecker( One of my favorites!)Fluke
  • Wifi AnalyzerWifi Analyzer

 

Active Site Survey

What is it?
This type of site survey does a more indeep study than the passive one, as you will be connecting a device or deveices to get more specifc infomration

What type of Data you can collect with it?

  • TCP Troughput(uptream/downstream)
  • UDP Trhoghput(Uptream/downstream)
  • Get an idea of the performance of the AP in expected scenarios

 

Example of tools used

  • Application that generates network traffic
  • Devices(laptops, smartphones etc)
  • Applications that can measure thoughput rate

 

Predictive Site Survey

What is it?
In this type of site survey you simulate with a program where should be placed the APs,  how many APs you need and all this is done by inputing some building plans in the soflware

 

What type of Data you can collect with it?

  • Number of APS
  • Placement of APS
  • Etc

 

Example of tool used

  • Visual RF(In our case)
  • Vendor specific simulator( Mosf of Wifi vendors got their own simulator)
  • AirMagnet
  • Etc

 

Survey Requirements:

You see that i have mention before Requirements? well when i say requirementes i mean things that you need to ask the client to take in mind for your design

 

  • Bussiness REquirements: Why is the bussines asking for Wifi? asnwering this can give you the idea of the wifi architecture you will need
  • Coverage vs Capacity:  Here you need to take in mind or ask the client how many devices will be connected to the wifi in a specific areas, so you know if you need more than one AP(Lately you will notice that most of the client are starting to pick capacity over coverage).  But still you will see some clients which just need coverage as they just want wifi for some random users and high level users like managers, owners, and other type of users like guest.
  • Devices Requirements: How much BW does the devices need? what kind of deivces are expected? there would be a lot of cellphones? if so you migh be thinking then that you need no less than an RSSI of -65 even -60 for those.
  • Cell Planning: Yes when you are doing High Density you need a Cell planning.  You will be using 20mhz or 40mhz channels on 5ghz? how many channels you would need?  Are you using dual band dual radio APS? then you should be thinking in surveying for 5ghz as well

 

This small techincal guide will give you an idea of what site survey is about i mean an overivew of it.

 

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Last update:
‎07-02-2014 12:05 PM
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Comments
KeithRParsons

I disagree with most of what is in this article.

 

Designing or 'Engineering' a wireless LAN is *NOT* a Site Survey.

 

A Site Survey is a component of the WLAN Design process. 

 

First - Define Requirements: this should take a bulk of the design time. It need to be detailed and complete.

 

Second - Design: this is the process of attempting to meet all the requirements while staying within the design constraints. Coverage is very easy to obtain... but keeping the CCI/CCC to a minimum is the most difficult part. An on-site assessment of the RF characteristics of the buildings will help with accuracy.

 

Third - Deploy: the easist bits... mounting the APs, configuring the controller, etc. One tip - be sure to ALWAYS test the wired drops for PoE, DHCP, DNS, Default Gateway, VLAN assignments, etc. BEFORE attaching any AP to the wired network.

 

Fourth - NOW we do a valdiation Site Survey. This is a required step in the WLAN deploment process. You MUST test and verify the installed WLAN meets all the design requirements. If you leave this step out... you are bound to have another truck roll to return and fix the WLAN in the future.

 

Coverage is easy!

 

The hard part of WLAN design is working to ensure you can achieve Frequency Reuse - without it. Adding more AP's does NOT give you more capacity - it just adds to Co-Channel Contention and lower overall throughputs.

 

 

Predictive Survey: A software tool based on RF mathematics and specific algorithms to simulate RF in your environment and to allow for an itterative approach to design. Design to meet requiremens while staying within constraints. Should be used with actual on-site measured RF attenuation values from the walls, and floors. 

 

Passive Survey: Software tool that collects RF data from all AP's in the area. Plots heat-maps to show where coveragea is and is not at certain levels. Can also be used to validate many of the design requirements - Primary RSSI, Secondary RSSI, SNR, Noise, and most importantl Co-Channel Interference.

 

Active Survey: much like the Passive Survey - only collecting data from a single Access Point at a time. VERY difficult to do correctly. You have to walk the site multiple times to ensure getting Active data from each and every AP being tested. And be sure to collect the data clear to the edge of each AP's coverage. Else you'll have false data and not collect the CCI areas that are the most difficult to find/fix. Active surveys contain some extra information not available in the Passive version. Like actual connected data rates, error rates, etc. But remember you are only collecting data for ONE AP at a time... takes a very long time to do an Active Survey properly and with accurate data.

 

AP-on-a-Stick Survey: Using only a single AP, this technique was used in the past to confirm coverage. Very difficult to obtain any of the other requirements other than Primary RSSI. Does not give you Secondary RSSI, or Co-Channel Interference at all. It may be used prior to deployment, but must always be followed up with a post install Validation Survey. Always!

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