When to Perform Wi-Fi Site Surveys

If we look at the process of deploying a Wi-Fi network, site surveying starts right after requirements definition and off-site network planning. As you probably remember from the network planning post, network planning was done to determine the AP locations, configurations and antennas. When deploying a Wi-Fi network, site surveys are performed to ensure our plan was correct, and to optimize the plan so that the network truly works. But that’s not all: walkthrough surveys are perfomed throughout the life cycle of the Wi-Fi network.

An example of a site survey tool: Green lines are the survey walking paths. The colored heatmap shows signal strength.

Pre-Deployment Site Surveys (“AP on a stick”) are performed using one or a couple of access points. The idea is to get an understanding of the Wi-Fi signal behavior in the environment before the network is purchased, let alone deployed. Ideally, pre-deployment surveys are performed after a careful network plan (see the post about network planning here) to ensure that the planned access point locations really will provide good coverage. Here’s the idea:

1. Power up the AP in the first potentially good location (these locations were determined in the network plan)
2. Perform a walk-through site survey to determine the coverage of that AP
3. Move the AP to the next potential location and power it up
4. Perform a walk-through site survey
5. …

If you repeat this as many times as you are planning to have APs, you will have a complete understanding on how the network is going to work – without purchasing all but just a couple of access points. Of course, testing the entire plan this way may be overkill, but performing this in a limited area does pay off.  Some trust their network plan skills (and software) so much that they skip the pre-deployment phase entirely.

Post-Deployment Site Surveys (“Verification Surveys”) are performed after the WLAN infrastructure has been set up. Walk around the site with a site survey tool, and get a full understanding of the coverage, connectivity, and performance – as they are on the production network. The more thoroughly you do this step, the better you’ll sleep at night (or at least the more you can trust your network).

Periodic Site Surveys (“Health check”) is a quick site survey around the site – not as thorough as post-deployment survey but rather a quick one. The idea is simply to check that the network still works OK from the client device point-of-view. After all, the APs are only monitoring your network from the ceiling (where the RF is quite different). And the RF is quite dynamic: structural changes and even furniture may change the RF environment quite a bit. Plus the infrastructure may not always work quite as your web-based Wi-Fi infrastucture dashboard view may show: It’s not uncommon to find out that APs seem to be working OK, but suffer from bridging issues, missing or incorrect configuration settings, even missing SSIDs.

You will also find rogue access points that your access points cannot detect (some rogues are only audible at the perimeter). I would recommend a health check  every 3 months or so.

Troubleshooting Surveys (“Something-hit-the-fan surveys”) can be minimized by performing periodic site surveys. Of course, every now and then, unexpected things do happen no matter what. To effectively troubleshoot, just perform a quick site survey in the problematic area. With this information, you can easily see what has changed compared to the previous surveys, and what is causing the current issue. For troubleshooting non-802.11 interference, use a spectrum analyzer.

BTW, some basic Wi-Fi troubleshooting guidelines can be found in this previous post.

Next time, let’s talk about different types of site surveys: active, passive, and RTLS calibration surveys.

Wi-Fi RF Site Survey Basics

The excellent CWNP Dictionary describes site survey as follows: “Site survey is the process of evaluating RF behavior in an environment and determining the best way to implement a WLAN based on this information”. Can’t argue with the CWNP. However, today the term “site survey” is used used to describe all kinds of tasks during the Wi-Fi deployment. The term means different things to different people.

Now that we started with literature, the CWNP Study Guide (I had an old version at hand, but anyway), states “A site survey is the most important step in implementing any wireless network”. In any environment where you need the Wi-Fi to truly work, you want to perform a site survey to ensure adequate coverage and performance with your network. For example: If you’re about to deploy an enterprise Wi-Fi network that supports voice, it’s probably not the best idea to listen to, let alone buy from, the folks that downplay the importance of a site survey.

Some Wi-Fi systems have an “automatic site survey” feature where the access points make some kind of a network self-check. I’m not sure if I would call a self-check “site survey” though. A site survey, in my view, should done on the ground level, where the actual users are. There’s quite a difference between RF signal levels on the ceiling and the floor level.

In the following posts, I’m referring to site survey as the process of performing a walk-through to acquire information about

• On-site RF characteristics,
• Network connectivity and performance, and
• Wi-Fi infrastructure setup.

How it’s Done

Typically, you would perform a Wi-Fi  site survey by walking around the site – probably carrying a light-weight laptop or tablet computer. On the computer, you have your site survey application installed – whether a map-based professional software or a basic signal strength indicator. Various network measurements are taken and recorded.

When using a professional site survey tool, you would frequently click your current location on the map as you walk around.  This way, the site survey application will know where you are at  all times. With the location information, the site survey app is able to construct Wi-Fi coverage and performance heatmaps after, or even during, your walk-through. This way, you don’t need to stop to manually document the measurements, but you can just walk around the site once and analyze the measurements immediately thereafter.

The heatmaps really make your WLAN visible: They can reveal coverage holes, interference issues,  areas of excessive packet loss, and unexpected data rate issues. And that’s just to mention a couple.

The site survey will also reveal the locations and other details about all the Wi-Fi access points.  You can locate rogue APs, see the MAC addresses, channels and SSIDs in your network, and drill into the 802.11n details.

In addition to the laptop-based surveys, there’s a few tasks that are typically performed:

• Photos of the environment and AP/antenna installations document better than a 1000 words
• Spectrum analysis spot checks provide a deeper understanding of non-802.11 noise sources
• If you’re deploying for voice, it’s probably a good idea to perform a few spot checks using an actual Wi-Fi phone. Good Wi-Fi phones have a  ”site survey mode” that’s very useful. Nothing like testing an actual call, though

That’s that for site survey basics. We’re going to talk about different types of site surveys in the next post.

Cheers,
Jussi Kiviniemi
Sr. Product Manager / Ekahau