WIRELESS INFRASTRUCTURE

  • 04/19/2016
    7:00 AM
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When You Should Disable 2.4 GHz Radios In A WLAN

A high number of 2.4 GHz radios and overcrowding in the 2.4 GHz spectrum can degrade WLAN performance.

WiFi doesn’t work. We need more access points (APs). These are common misconceptions I hear. More radio frequency (RF) is not always better, especially if it is 2.4 GHz RF. In fact, adding more access points can actually hurt WLAN performance.

In this post, I'll explain why you should disable most 2.4 GHz radios to avoid channel overlap and begin designing 5 GHz wireless networks for better WiFi performance.

2.4 GHz is congested

Most wireless networks have neighboring tenants occupying the same 2.4 GHz frequency band. When two or more APs are on the same channel, they operate within the same contention domain.

Because of the half-duplex nature of WiFi, each device needing to communicate will contend for air time. When two or more APs are on the same channel servicing the same area, each device associated to those basic service sets (BSS) will need to contend with each other to communicate. This is co-channel interference or co-channel contention.

Limited channels

In the U.S., we have only three non-overlapping channels to utilize in a channel reuse plan. Once three access points are deployed, care must be taken to avoid channel overlap.

This is not enough channels to deploy WiFi in a large office environment, and it falls completely short in high-density areas.While some wireless engineers will argue that placing the APs far enough will not cause co-channel interference, I beg to differ.

The signal in which a device, or even an AP, detects energy varies. If, for example, a smartphone may not sense energy on channel at -70 dBm, the threshold may be set higher at the AP level, such as -80 dBm. This is worth considering in a channel reuse plan, but any design should be validated.

Design for 5 GHz

As a result of 2.4 GHz overcrowding and lack of sufficient non-overlapping channels, my suggestion is to leverage 5 GHz as much as possible.

Begin with disabling 2.4 GHz radios when channel overlap occurs. Of course, you will want to consult your WLAN design and perform validation after making the changes. It's my opinion that where there is a coverage gap in 2.4 GHz, it will be filled with 5 GHz.

There is a caveat with this strategy: You must know what devices are being used on your network before disabling 2.4 GHz radios. These recommendations will have less impact if the network is primarily occupied with 2.4 GHz single-band devices.

After reducing the number of2.4 GHz radios, proceed with designing wireless networks for 5 GHz. Instead of enabling proprietary band-steering features, lower the transmit power of 2.4 GHz radios below the transmit power of 5 GHz radios.

In the 5 GHz frequency, there are 24 non-overlapping channels using 20 MHz channel widths. Channel overlap can be minimized greatly. In addition to the many channels available for reuse, 5 GHz has less congestion than 2.4 GHz.

radios-2.png

WiFi channel allocation
Caption Text: 

(Source: SecurityUncorked.com)

 

Do not go above 40 MHz channel widths. 80 MHz and 160 MHz channel widths are only appropriate for home use; they are not advantageous in the enterprise. This is due to the number of available non-overlapping channels, and we're now just beginning to see devices come to market supporting the wider channels.

Don’t be afraid to use dynamic frequency selection (DFS) channels to fully utilize the 24 non-overlapping channels. Be prepared to check your logs for any DFS events and optimize accordingly. Without DFS channels, there are still nine non-overlapping channels.


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