The fundamentals of Wi-Fi have been preached for many years now, however, many deployments still fall short with users encountering poor performance. Starting with the basics will lead to a better design; and as the industry pushes for more available Wi-Fi spectrum, knowing the fundamentals will help minimize a lot of wasted spectrum.
We have two available bands to utilize for Wi-Fi traffic. Since the ratification of 802.11 prime, we’ve had 2.4 GHz. Currently, 802.11b/g/n, and future 802.11ax, operate in 2.4 GHz. Often it is considered an unusable or “junk” band due to congestion caused by an influx of Wi-Fi devices over the past 10 years. IoT has shown to be a driving force in using 2.4 GHz in the last few years.
Because the 2.4 GHz spectrum operates in unlicensed frequency, many manufacturers have relied on this band to drive consumer growth. But the spectrum became full of devices communicating on poorly configured access points, leading to high channel utilization in 2.4 GHz.
There are only three non-overlapping channels to work with; 1, 6, and 11.
Author: Michael Gauthier, Wireless Networking in the Developing World
The image above depicts the 2.4 GHz band with 14 available channels – while this is true, many of the channels overlap each other due to their 22 MHz channel width.
Note: Access points operating on overlapping channels must share the same capacity. With Wi-Fi operating in half-duplex, we will see a degraded performance in networks in medium-to-high density or capacity.
Looking at the image above, again we see three non-overlapping channels. This is the most important reason for using 20 MHz channel widths. Be sure to avoid channel bonding in the 2.4 GHz spectrum.
To address the issue of channel overlap and to provide more capacity, there is the 5 GHz spectrum. There are 24 non-overlapping channels which is eight times as many channels that are available with 2.4 GHz.
The 24 channels are available when configured with 20 MHz channel widths. When channel bonding to 40 MHz channel widths, it drops down to 12 non-overlapping. Stepping up to 80 MHz channel widths lowers the non-overlapping channels to 6, and with the latest amendments, an engineer can channel bond to provide two non-overlapping channels at 160 MHz.
The problem with channel bonding is the amount of noise floor increase. There is essentially double the noise which means the SNR of a wireless device will need to be higher in order to achieve the higher data rates.
Additionally, some devices may not be able to support 80 MHz or 160 MHz channels yet alone, take advantage of those channels.
Within 5 GHz there are Dynamic Frequency Selection (DFS) channels available for network engineers to use. With more channel selection the amount of capacity is increased. It allows for more channel reuse in an environment without cause an excessive amount of channel overlap.
When designing a wireless network, take channel reuse into consideration. Having too many access points operating on the same channel within the same area will cause co-channel contention. This effectively creates one shared capacity area in the channel.
Wi-Fi is a listen before speak technology. If there is a device or access point transmitting on a channel and another device or access point on that same channel hears that communication it will need to hold off before it can transmit.
To create an effective channel plan, use site survey planning software. Minimize the contention domains (channel overlap) and then validate the design post-deployment.
Within NetBeez, you can also find out how many access points an agent can hear and on what channel.
When it comes to channels, here are some tips that can be easily implemented. The first one is to stay with 20 MHz channel widths – it provides you with a plan for more channel reuse. If you need more bandwidth you can possibly step to 40 MHz channel widths.
Secondly, be sure to utilize DFS channels. Test to ensure you’re not seeing any DFS hits from legitimate sources such as radar but if you don’t see any go ahead and start using DFS channels into your plan.
Tip number three: Stay away from using the out-of-the-box default settings. Wi-Fi networks are all different and require different tuning. If your wireless system uses 80 MHz channel widths by default, think about how that affects your environment.
Lastly, validate your design and changes using site survey software and tools. This will provide you with the visualization and the affirmation of your deployment. From there, tune as necessary.
About the Author:
Rowell Dionicio is a network engineer for a west coast university specializing in Wi-Fi design, deployment, and troubleshooting. He supports a WLAN infrastructure with over 40k concurrent Wi-Fi devices in higher education. He is the co-host to a Wi-Fi focused podcast, https://cleartosend.net and is co-host on a YouTube show ‘WiFi of Everything’. You can engage with him on Twitter @rowelldionicio where he encourages open communication.