Wireless Site Surveys

Passive Surveys

What is a Passive Survey?

This is the most common type of Survey performed and normally would be utilized in troubleshooting an existing network or for the validation of a newly installed wireless network. It involves walking the area concerned and gathering data on the existing wireless coverage. It’s called passive as you don’t join the wireless network, you just effectively listen and record the key metrics about the coverage. Typically, the metrics are the signal strength and noise readings for all the SSIDs you can see being broadcast. In some instances, we will see your neighbor's network.

Why use a Passive Survey?

The advantage of this method is that it answers the most common question about wireless, “Are there any holes in the coverage?”. This is also becoming a moving target, as we are finding older APs where the power on the radios is slowly failing, but also newer technologies demanding a higher specification of wireless coverage. Hence just having some wireless in an area is no longer good enough.

The survey image above shows where you have walked (the dotted lines), whilst the differing color shading indicates the signal strength. Using this data you can then predict the likely speeds a connected device is going to achieve.

Potential Drawbacks of a Passive Survey

The biggest issue with this type of survey is that modern laptops don’t offer up the noise information anymore, hence the need to use a dedicated tool for gathering the signal data as noise and Signal Noise Ratio (SNR) are key measurements you really need to know. We use dedicated data-gathering devices to solve this.

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