Introduction

There is a lot that goes into configuring a strong, healthy wireless solution, and one of those areas of focus is Wi-Fi Channel Overlap and Interference. However, it’s not a simple focus, it is multi-faceted.  Following are the high-level points that need to be considered and addressed.

2.4 GHz Channels

The 2.4 GHz spectrum is in total only 100 MHz wide. While there are up to 13 channels that can be selected, only 3 channels (1, 6, 11) provide non-overlapping channels. Each of these channels have a width of 20 Mhz. Overlapping channels can lead to Co-Channel Interference (CCI) and Adjacent-Channel Interference (ACI), which can degrade wireless performance. 

Adjacent-Channel Interference

ACI can occur when two criteria are met: devices or networks operate on channels that are not the same, and those channels are adjacent. For example, you could have an AP on channel 6 and another on channel 3, which could create interference if the channels overlap.

Unlike CCI, in ACI, devices don’t “understand” each other’s signals since they are not on the exact same channel. They won’t use mechanisms like CSMA/CA to coordinate access, which can result in devices transmitting over each other and causing interference.

Co-Channel Interference

CCI occurs when multiple devices or networks operate on the same channel within close proximity. For example, if two neighboring Wi-Fi networks both operate on Channel 6 in the 2.4 GHz band, they become a single cell coverage of that channel even though they are independent of each other.

In CCI, devices “see” each other’s signals since they’re on the same channel. This means they can utilize the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol to manage access to the shared medium. Essentially, devices will listen before they transmit, and if the channel is occupied, they will wait for it to become free. While not as bad as ACI, it will still degrade performance.

5 GHz Channels

The 5 GHz spectrum is increased to 25 non-overlapping 20 MHz channels. This means that, unlike the 2.4 GHz, each channel can be selected without worrying about overlapping. But if you decide to stay at the 20 MHz frequency, you are limiting your bandwidth.

To increase your bandwidth, the 5 GHz spectrum has a 40 MHz and 80 MHz frequency. It also has a 160 MHz frequency but that is another discussion for another day. To simply put it, a single 40 MHz channel bonds two of the 20 MHz and 80 MHz is a bond of two 40Mhz, each time effectively doubling your theoretical bandwidth. This sounds great, you could probably just set your entire network to 80 MHz channels. But you will need to plan the placement of your AP’s and channels to avoid causing co-channel interference.

Let’s say we have a square room with an access point in each corner of the room. If we were to set all access points to channel 42 (which is an 80 MHz channel) we gain the expanded bandwidth, but now all the APs operate as a single cell. Devices must now deal with co-channel interference and wait for each other to transmit data. The 80 MHz frequency has a total of 5 non-overlapping channels. If we wanted to, each AP in our scenario can be set to their own channel without worrying about CCI. But as we grow in size and additional AP’s are added, we need to consider placement of the new APs so that they don’t become a cell with each other. By sacrificing bandwidth, we can utilize the 40 MHz frequency instead. The 40 MHz frequency has a total of 12 non-overlapping channels which increases the usable channels without causing CCI and allowing more placement of access points.

Lastly, another thing to consider is that, when changing to 40 MHz and 80 MHz, you are introducing an extra 3db of noise each time. An 80 MHz channel will have an additional 6db. This lowers the Signal-to-Noise ratio, which could lower your MCS rate. Lower MCS rate means lower throughput and bandwidth, effectively negating any of the benefits of the 80 MHz channel.

Conclusion

Wireless environments can be complex, and not everyone can be a wireless expert. If it’s not your area of expertise, and you don’t have the time to become an expert, Navigator Networks can help fill that gap. We have the tools and experience to build visual, predictive wireless designs for new deployments, troubleshoot existing deployments, and make improvements. Click here to take the first step in improving your wireless experience!