• Andrew Campbell

Where do I place my APs?

Updated: Sep 4, 2018

How to determine where to place Access Points depends on network requirements and careful analysis of the RF environment.

As someone with a MSEE with a focus in RF engineering, I am always thrilled when I get a chance to discuss RF designs and propagation theory. Determining Access Point placements was one of the first tasks I was exposed to in my early Wi-Fi career and I never looked back. Over the years I have fine tuned the way I design the layout of my APs, below are the steps that I follow:

1. Gather Network Requirements

Sit down with stakeholders to determine what features, performance, devices, and applications that will have to be supported. Designing a network for Wi-Fi connectivity is different from a Wireless Intrusion Detection System (WIDS). Additionally, some applications such as real-time video require more stringent network latency requirements.

2. Visually Survey the Facility

When I use the term survey in this context, I am referring to physically walking the facility while noting the construction materials used, any potential interference sources (to avoid certain channels or mitigate), and note any neighboring networks or interferers (consider airports for DFS concerns).

3. Utilize a Wi-Fi Predictive Modeling Software Tool

Early Wi-Fi engineers used a shall we say, install and pray method of AP deployment with the intention of filling in the gaps of Wi-Fi coverage. As Wi-Fi became a critical business asset and no longer a best effort deployment, the need for a more detailed design was required.

Along came Wi-Fi site surveying software tools and predictive modeling to follow soon. In the early years of these tools, the site surveying features predated the predictive models where engineers would perform what is commonly known as AP-on-a-Stick (APoS) surveys. APoS surveys are exactly what they sound like, they involve placing an AP on a pole/tripod while taking RF measurements to verify the coverage area, AP cell overlap, and attenuations between walls/floors. Some engineers still swear by this method, but it has largely grown out of favor as it is labor intensive and often an unnecessary step as long as thorough a design is met with the later steps discuss here.

Later these Wi-Fi tool vendors started to provide predictive modeling features that offered a way to simulate a Wi-Fi deployment. The software requires you to input the floor plans of the facility, enter information about the wall/floor materials (attenuation), placement of the APs, the models of the APs, and the transmit power levels, antenna pattern, and antenna pattern direction. These tools use RF propagation models (ray tracing, path loss, and other RF algorithms) to simulate what the coverage of the network based on the AP placements and the building inputs you provide.

Commonly used tools: Ekahau Site Survey, iBwave, AirMagnet

4. Install the APs Based on the Predictive Model

Place the APs in the locations that were determined in the previous step.

5. Configure the APs Following Best Practices

This would be another whole blog post, but follow industry best practices when it comes to configuring the APs. This may include removing 802.11b data rates from the minimum data rates, reducing the size of the transmit power ranges, optimizing the channel plan, using 20/40 MHz channels instead of wider bandwidths, and other widely recommended configuration best practices.

6. Validate the Deployment

This step may include a site survey utilizing on of the tools mentioned in step 2, using a network management system (NMS) to monitor performance, and/or using physical sensor/software tool to analyze the network.

Site surveying entails using a software tool to measure the Wi-Fi characteristics of a deployed network (signal strength, channel overlap, noise, SNR, etc.).

Network management systems (think Aruba AirWave or Cisco Prime) usually have features that can monitor in real-time (or close to it) the Wi-Fi performance statistics of the network. Some of these tools even include the ability to add a floor plan such that you can see the RF heatmaps of the building.

Finally, one of the newer methods to monitor Wi-Fi performance is to use sensors along with accompanying software to analyze network statistics and even look at the application layer. For more information, see the following companies: Cape Networks and 7 Signal

7. Continued Monitoring and Optimization

The work is never done for a Wi-Fi engineer. There are always more clients to serve, new devices, new network protocols, additional security threats, building layouts changing, and much more to be concern about. In order for Wi-Fi networks to continue to operate at peak performance there needs to be continued monitoring and ongoing optimization efforts. Anytime there is a changed to the environment, there should be a reassessment of the deployment.