It is important to perform a wi-fi survey so that you can determine not only the perfect place to locate your access point or bridge but to gain an understanding of the channel co-existence challenge you may face. With wireless access points in surrounding neighborhoods and businesses, you will need to perform a survey by walking around and mapping out the BSAs (Basic Service Area) of wireless that surrounds you and your organization.
Below is an example of our school’s perimeter. Matt, Chris and James, students in the Computer Information Technology, class performed a survey using a Microsoft GPS and Vistumbler. This survey revealed access points and their channels of current wireless at our institution and includes APs in surrounding businesses and neighborhoods. These were mapped using Google Earth after exporting their KML file from Vistumbler.
This type of survey allows IT professionals to analyze data exported to ensure the correct channels can be used at their organization.
After exporting the wireless information, you can analyze each access point or wireless device by clicking on it. Below is an example of the information exported into Google Earth. Each device shows SSID, Network Type, Mac Address, Channel, Security, Encryption Type, Data Rates, Latitude, Longitude and Manufacturer information. Analyst using this information can also determine the best placement of wireless devices along with channel information.
Channel co-existence is when access points share channels that are very close to one another.
802.11 wireless on 2.4 Ghz has three non-overlapping channels. These channels are 1, 6 and 11. The closer channels are, the more likely interference will take place. With the amount of wi-fi in use today, IT professionals have to chose between 2.4 Ghz and 5 Ghz and and try to select channels that are not in use if possible. Professional access points and bridges can also adjust power as necessary. A dense population can make this very challenging.
If you look at the students’ survey by zooming out to see how many access points can be seen, this is what you are looking at! Now you can see why site surveys are important at your organization.
In addition to this survey, a secondary survey using a spectrum analyzer is very important to search for interference from other sources. (See our review of the Airview Spectrum Analyzer)
Channel information (Chart from Wikipedia)
Here’s another look at a wireless survey showing vertical lines and signal strength. (James M. KML survey)