By Dylan Rhodes posted May 17th 2012
The Vengeance® 2000 7.1 Wireless Gaming Headset receives and transmits digital audio over what's colloquially referred to as the 2.4GHz band. More accurately, the band extends from 2.404 GHz to 2.478 GHz, and it's known as one of the ISM bands. ISM stands for “Industrial, Scientific and Medical,” and the band was originally allocated for — as you can imagine — industrial, scientific and medical purposes other than communication.
These devices are segregated to the 2.4GHz range to keep them well away from radio communications, so they won't cause interference.
With only so much frequency spectrum available, this band was later opened up for use by low-power communications equipment that's capable of dealing with interference from ISM devices. In short, digital transmission protocols with the necessary error correction measures in place to keep functioning even when the band is very crowded.
802.11b and 802.11g routers use this band. So do some cordless phones, mobile phones with walkie-talkie features, and Bluetooth devices — not just the ubiquitous Bluetooth earpieces, but BlueTooth wireless speakers and other gadgets.
At first glance, this might sound scary — when you're using a 2.4GHz device, not only do you need to worry about electromagnetic interference from ISM devices, but there's also the danger of collision with other digital wireless communication devices, right?
Adaptive Channel Hopping
Since the makers of BlueTooth devices, wireless networking equipment, and — yes — wireless gaming headsets — want their products to work well, a lot of time has been spent by smart people to help ensure that all of these unlicensed devices play nicely with each other. Vengeance 2000 uses a technique called adaptive channel hopping, also known as adaptive frequency hopping.
Like so many other technologies in common use, it was developed during wartime, for secure communication over the US Signal Corps SIGSALY system and remote control of torpedoes. It was independently invented and patented by several people, including one Hedy Kiesler Markey, also known as Hedy Lamarr. Her patent is available for viewing.
First-generation consumer 2.4GHz communication devices — think first-generation BlueTooth earpieces — used basic channel hopping. The method was remarkably simple and brute-force: they would randomly jump between the approximately 80 available channels in the 2.4GHz ISM band. No checking was performed to determine if a channel was clear before the device jumped to it. Since the jumps were performed 1,600 times per second, the theory was that if there was a random collision, data would be lost for just one 1600th of a second before your earpiece jumped to the next channel, and you could continue with your conversation without interruption. Collision could occur either with another device using random channel hopping, or with a device (such as a wireless router) using a dedicated channel.
But as more devices began using this band, there was a growing risk of noticeable channel collision — colliding enough times in a row to result in a period of signal loss that's long enough to notice.
Without interference from other ISM band devices, the Vengeance 2000 has unrestricted use of the band.
Adaptive channel hopping solves this problem. It uses a number of algorithms to determine if a channel is already in use or otherwise shouldn't be used, and then simply stays away from those channels.
In other words, when you turn on your Vengeance 2000, within milliseconds it's figured out where your wireless router is operating, and it makes sure never to venture into those channels.
If your neighbor turns on his wireless router halfway through your gaming session, the Vengeance 2000 knows that before there's the chance of it noticeably interfering with your audio.
If it detects the presence of another device using part of the band (in this example, an 802.11g router using channel five), it marks that portion of the band as off limits and constrains its frequency hopping to known good channels.
Channel collision is still possible; for instance, the Vengeance 2000 wireless headset and another channel-hopping device might try to jump on the same channel at the same time. But, this will be a rare occurrence in most real-world environments, and the collision will last for only milliseconds. A lot of engineering hours have been spent to ensure that you simply won't notice when it happens, so you'll enjoy uninterrupted gaming audio.