Wi-Fi site-survey tips: How to avoid interference, dead spots

Here’s how properly executed site surveys can make for better performing Wi-Fi networks by dealing with potential frequency conflicts, blocked signals and more.

Wi-Fi can be fickle. The RF signals and wireless devices don’t always do what’s expected – it’s as if they have their own minds at times.

A Wi-Fi network that’s been quickly or inadequately designed can be even worse, spawning endless complaints from Wi-Fi users. But with proper planning and surveying, you can better design a wireless network, making you and your Wi-Fi users much happier. Here are some tips for getting started with a well-planned Wi-Fi site survey.

Use the right tools for the job

If you’re only trying to cover a small building or area that requires a few wireless access points (AP), you may be able to get away with doing a Wi-Fi survey using a simple Wi-Fi stumbler or analyzer on your laptop or mobile device. You’ll even find some free apps out there.

Commercial options range from a few dollars to thousands of dollars for the popular enterprise vendors.Using a simple Wi-Fi stumbler or analyzer, you can walk around while looking at the signal level of the APs you’re surveying to get an idea of the signal propagation, coverage boundaries, and possibly the data rates.

This is an on-the-spot approach; you would visualize in your head where the coverage boundaries are, or sketch them on a floor plan or map of the area.

For networks that will require more than a handful of APs, a map-based survey tool is recommended. There are some free or low-cost options, but the popular enterprise-level solutions go into the thousands.

AirMagnet Survey from NETSCOUT

Using a map-based survey tool (pictured) allows you to load a floor plan or map of the area into the software and then walk around while marking your location. In the end, you have a heatmap of the signal, noise, signal-to-noise ratio, data rates, and other results. This allows you to better visualize the coverage and performance of the APs and any neighboring networks. It also provides a better way to save and view the data after the fact than what you’d get using a Wi-Fi stumbler or analyzer.

Some map-based tools also allow you to do full predictive/simulation surveys without being on site, which can be cost-effective if done correctly and allows you to survey future builds.

Choose the right survey AP, antennas, and test clients

When surveying, use the same AP and antennas that will be installed. However, try to use any autonomous model or mode so you don’t have to wrangle with a wireless controller. Configure the AP as closely as you can to the settings that will be deployed, especially the frequency bands, channels, transmit power, 802.11 mode, and security.

Use realistic transmit power levels for the survey AP. Typically you want the total effective isotropic radiated power (EIRP) of the AP and Wi-Fi clients to be similar, which usually means using a much lower level on the AP compared to its maximum. If adding or modifying an existing network, perhaps look at the average power levels of the existing APs.

During surveying, use the same AP antennas that will be installed as well. If you’re using an AP with detachable antennas and are going to use additional antenna cable, consider that when selecting the transmit power levels so you have the EIRP that you desire.

Also consider the Wi-Fi clients you use for the surveying. Due to the limited number of clients supported by surveying software, you may not be able to choose a very good representative client depending on the various clients that will be used on the network. However, some map-based survey tools allow you to simulate other client types and show simulated heatmaps based upon the survey data collected. Even if the tool doesn’t allow this, you can do a rough simulation by adjusting the minimum signal levels when designing the network.