Why is RF Spectrum Management/ Radio management important in Wireless networks?

This article discusses why is RF Spectrum management / Radio management is crucial in wireless networks and how wireless controllers help managing the same. We look at co-channel interference and its effects on neighbouring AP’s, how co-channel interference is minimized by controllers, and the options available for optimizing the performance of wireless clients by managing the RF Spectrum better.

Why is centralized RF Spectrum management exciting?

¤ The controller automatically assigns the channel and power settings for all access points, which otherwise needs to be done manually in a dynamically changing environment which is hard.
¤ It reduces co-channel interference and hence enables dense wireless client deployments.
¤ By enabling even distribution of clients across the available channels, the performance is enhanced.
¤ Utilizes the 5 Ghz channel more frequently (for clients that can associate with it) and hence improves the performance.
¤ By controlling the air-time allocation ratio, the performance of the faster clients (Especially with 802.11n clients) is improved.

What is Co-Channel interference in wireless networks and how a wireless controller helps?

Well, in Wi-Fi access, there are two popular bands which are used by all access points – 2.4 Ghz or 5 Ghz. There are only 3 channels in 2.4 Ghz band that are non-overlapping. That means, at any time the wireless clients (laptops) can connect to any one of these channels. And there are 23 channels in the 5 Ghz spectrum. When two or more neighbouring Access Points have clients associated with them in the same channel, there is bound to be interference. This interference degrades the performance of a wireless network and hence needs to be taken care. A wireless controller needs to ensure that no two clients from nearby access points are connecting in the same channel. While most controllers do that, some allow the clients to associate in the same channels in the neighbouring access points, but control them well enough to avoid interference.

This feature of the wireless controller enables dense deployments of clients in a small area – typically this helps the education segment / conference hall kind of deployments where a lot of clients would be sitting in a small area accessing the wireless network simultaneously.

Distribution of clients across the channels:

Certain controllers also distribute the clients that are associating with the access points in a dense area evenly across the available channels. This ensures that no particular channel is over loaded. This greatly helps the wireless access performance in a real time scenario.

Utilization of 5-Ghz Channel:

Normally, even though an access point is capable of dual radio – 2.4 Ghz and 5 Ghz, there is a probability that most of the clients are associated with the 2.4 Ghz radio. Some of them may be capable of 5 Ghz too. Certain controllers push such clients which have dual capacity, over to the 5 Ghz spectrum. This spectrum not only has more channels (for a more efficient distribution among them), it is also less crowded – meaning, the SNR ratio is higher in a 5 Ghz spectrum as interference from other sources in the same spectrum is very rare. That is one of the reasons, why the access points and the clients need to have dual-radio capability, where ever possible.

Controlling the Air-time allocation ratio:

In a real time scenario, all types of clients connect to the access points. Some of them may connect in 802.11b, some in 802.11g,a and some more in 802.11n. So, the speeds at which they connect is also different – b being slowest, and n being fastest. Some controllers make the airtime allocated to different radios follow a certain ratio (Where more airtime is allocated to 802.11n based clients and less airtime to 802.11b radios). It makes sense, as the clients connecting with 802.11b radios are anyway going to work slower, and by allocating a lesser air time to them, the performance of the faster radios like 802.11n is increased.

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