CTS 170: APoS Site Surveys

Historically, AP-on-a-Stick (APoS) surveys were the only way to find out where to place the access points. We didn’t have any of the fancy software we have today to predict how the Wi-Fi signal will behave in our space. However, we still perform APoS today. In this episode, we will explain why we still use them and how they can be beneficial to us Wi-Fi Engineers.

APoS utilizes an AP that will be deployed on-site. The AP would be installed on a “stick” and is used to measure how the Wi-Fi signal behaves in the space that is being surveyed. The advantages are it takes into consideration the behavior of an RF wave and the attenuation, reflection, diffraction, scattering, etc. The disadvantage is it takes time and materials to achieve.

Historically, that was the way we used to define where to place the APs. We would start in a corner of a building and place the first AP, measure the signal to define the edge of the Wi-Fi cell and go on to the next measurement until you covered the whole site and defined the different AP locations.

The introduction of tools allowed us to model and predict how the Wi-Fi signal will propagate in a given space. This allows us to plan and perform our Wi-Fi design “on paper” so to speak. In order for this type of predictive design to be accurate, we still need to understand the physical environment. However, we can predict the signal prediction in the software and save some time.

Why do we still use APoS then? In some environment and cases, the predictive design will not be accurate enough for us to be confident in the design. In these cases, we now use the APoS to validate some of the AP locations defined during the predictive design phase. How much validation do we need to do? It depends 🙂

What material will you require to perform an APoS? The APs and antennas you will be using for your deployment. If you are not too sure which AP or Antenna will be used, test multiple models. A stick (tripod, poles…). If you need to go very high, you might need a scissor lift or other heavier tools. A bracket to install the AP and antenna on (Wi-Fi Stand). If you are planning on using specific angles, it could be useful to have a bracket that displays the angle. A battery to power on the AP. Venvolt from Ventev, Accelerator from AccelTex, A long ethernet cable to connect the battery to the AP (I like the flat ones), A water bottle, Useful add-ons: flashlight, Duck tape, zip ties, marker, security boots, yellow vest, ear plugs, safety glasses.

How do you prepare an APoS? You will need to configure the access point. Configure the access point in a standalone mode. Each vendor has their own way of doing it. Cisco using Mobility Express, Aruba using Instant AP, Meraki using the Survey Mode.

I like to configure 1 SSID per band so that I can analyze the results in an easier matter afterward. It also helps me to make sure I am walking far enough to reach the edge of both frequency cell edge. I use the transmit powers used for the design. You can use the channels you want. In order to plan for the worst case scenario, you could choose the highest channel you can use in your space. (Channel 11 on 2.4GHz and Channel 165 on 5GHz). You should also have your predictive model ready before going onsite for the APoS measurements (as much as you can).

How do you perform an APoS? How do you choose which AP location to test? Place the APoS exactly how you would install the AP in production. Turn on the AP and wait for the SSID to be broadcasted. Use your favorite survey software to measure the signal in passive mode. Keep an eye on the signal strength you receive and make sure you walk past your threshold. Once you are done, freeze your AP (in Ekahau) before you move the AP to the next measurement. Try to document your work as you go by taking pictures of the AP at its measurement location and put in notes in your site survey software.

Analyze the results and compare how the signal propagates in the real world and what you had in the predictive design. Adjust your model so it matches the real world. It will be an iterative process and both can be done on-site while you do your APoS.

Things you can also do while you are on-site: Validate the AP locations will work for all the location you have defined in your predictive model. Mark the AP location if you want to. Test the different options such as height and antennas. Take a look at how the users use Wi-Fi.

Links and Resources