Cells and co-channel interference

In high density deployments, multiple APs are used, and each one services an area called a cell. However, these cells can cause interference with each other. This is a common problem. The radio signal from one AP interferes with, or cancels out, the radio signal from another AP.

In the following diagram, note the interference zone created by one radio, causing interference on its neighbouring APs.

The interference zone can be twice the radius of the signal, and the signal at its edge can be -67dBm.

Reducing co-channel interference

For best results, use a ‘honeycomb’ pattern as a deployment strategy. The idea is to stagger repeated channels furthest from each other to avoid interference.

Best practices for Layer 3 and above

For TCP/IP layers and above, a common source of latency, or slowness in the wireless traffic, is too many broadcasts or multicasts. These types of issues can result from non-business and/or unwanted traffic.

To resolve issues at the TCP/IP layer and above:

• Identify business-critical applications.
• Use Application Control, Web Filtering, Traffic Shaping, and QoS to prioritize applications.
• Identify unwanted traffic, high-bandwidth web-related traffic, and use Security Profiles.
• Use the traffic shaper on a policy to rate-limit this traffic. These configurations are performed directly on the FortiGate.