Wireless Ethernet

802.11

802.11b occupies 83.5 MHz (for North America) from 2.4000 GHz to 2.4835 GHz.

802.11a occupies 300 MHz in three different bandwidths of 100 MHz each:

802.11b provides 11 channels (for North America), each channel being 22 MHz in width, and each channel centered at 5 MHz intervals (beginning at 2.412 GHz and ending at 2.462 GHz). This means that there are only 3 channels which do NOT overlap (channels 1, 6, 11).

802.11a provides 12 channels, each channel being 20 MHz wide, and each centered at 20 MHz intervals (beginning at 5.180 GHz and ending at 5.320 GHz for the lower and middle U-NII bands, beginning at 5.745 GHz and ending at 5.805 GHz for the upper U-NII band). It is important to note that NONE of these channels overlap.

The 900 MHz band is subject to channel etiquette. To comply with the FCC rules, they must not transmit at more than 1W, and they must not use the same frequency for more than 0.4s out of every 20 seconds, which is why they hop around in a pseudo-random order between 162 different channels in that frequency range. As well as allowing them to comply with the FCC rules, this channel hopping makes the radios relatively immune to interference -- if there is interference on one channel, they automatically switch to another one.

Internet Technical Notes and Resources

Last updated by Henning Schulzrinne