802.11b-g Wireless Interference

Dueling wireless signals makes for interesting home appliance setups. Many homes these days have wireless routers for devices like computers and game consoles. Granted, it’s much easier to setup wireless routers to distribute Internet connectivity than wiring the entire home, so wireless popularity is no surprise. However, as wireless popularity increases, so does the density of wireless signals, and interference becomes a factor in devices’ functionality.

In the past year, I have added a new dual band wireless router that has transmitters for 802.11a-n signals at 5 GHz and 802.11b-g at 2.4 GHz. This new router works very well with the mix of wireless computing devices our family uses, which includes an HP PC, a couple MacBooks, and iPhone/iPod Touch devices. Some devices use 802.11g and a few use 802.11n. We no longer use a cordless phone at home, so that potential interference is gone. However, I introduced a new wireless speaker system from Sony, called the S-Air, which operates in the 2.4 GHz area.

Sony does mention in its documentation about potential interference of 2.4 GHz signals, and there are 3 channel settings labeled A, B and C for pairing up between the transceiver and the remote speaker’s transceivers. The humorous part of the S-Air documentation is that Sony shows only how to work around wireless conflicts with neighbors with other S-Air systems. In fact, Sony should have known to write documentation to reflect the more likely cases of 2.4 GHz wireless routers. Sony should also publish the three (3) frequency ranges for their S-Air system, so that wireless owners can manually adjust their frequency channels and reduce interference issues.

The current 2.4 GHz wireless channels on wireless routers is numbered 1 through 13, though my Apple Airport and most Linksys and D-Link wireless routers only have channels from 1 to 11. The channels start with Channel 1 at 2.412 GHz and increase in increments of 5 MHz (or .005 GHz) up to Channel 13 at 2.472 GHz. Any given wireless channel has a frequency bleed of 22 MHz that can cause the interference. See the graph below for the frequency bleeding diagram. In order to prevent wireless interference in a home, wireless transceivers need to be set to channels at least 22 MHz apart, which equates to Channel 1, 6 and 11 for three device setups.

Wireless Frequency Bands

Back to my experience with Sony S-Air and my Apple Airport: The S-Air units were set to Channel A and an unknown frequency, while the wireless router was set to Channel 1 at 2.412 GHz. The Sony S-Air speakers were intermittently dropping off and then re-linking to the Sony’s main transceiver. I reconfigured the Sony S-Air system for using its Channel B. The interference continued and the speakers dropped the S-Air link as before with Channel A. It was time to approach the problem from the router side.

I launched the Airport Utility, logged into the configuration screen for wireless and manually adjusted the 2.4 GHz band to use Channel 11, which is at 2.462 GHz. Since this was a full two band range away (50 MHz), there was little chance of interference, unless the Sony S-Air channels had a wider frequency band. Once the wireless router rebooted, the interference problem cleared up and for now the problem seems to have been remedied.

I did not scour the internet to find the specifications for Sony S-Air and the frequencies that they operate on and how they compare to wireless router channels. I do feel confident that S-Air operates close to the 2.412 – 2.32 GHz range, since the interference was happening there with my wireless router. So, if you are using the Sony S-Air or some other comparable wireless system in your home and interference is a problem for you, adjust those wireless channels so you can enjoy your technology to its fullest extent.