What is a wireless channel?

Question

As the question , I don't really understand what is a wireless channel.

Supposed we have an access point with the standard 802.11b, it will use the frequency 2.4 GHz -->Is this the bandwith? And the transfer rate of this standard is 11 Mbps. What is the relationship between them? and why do we have to divide the bandwith into different channels?

Thanks in advanced.

Answer 1

2.4GHz is the frequency at which the wireless channel exists. In reality 802.11b uses the radio frequency spectrum from roughly between 2400MHz to 2450MHz which is divided into 11 channels (sometimes 13 or 14 channels, depending on regional regulatory laws). Separation into channels is done simply to allow multiple wireless channels to coexist.

The image below from Wikipedia illustrates the separation into channels pretty nicely:

The bandwidth of each channel is 22 MHz for 802.11b specifically, the other variants of 802.11 allows various other bandwidths. This is defined in the 802.11b specification.

The maximum data-rate of 802.11b is 11 Mbit/s. 802.11 supports data rate adaptation, which means the communication system will adapt to the current signal-to-noise ratio (SNR). Lower data rates are more robust against noise. The data-rate is related to the bandwidth of the channel, but depends on the modulation used.

This does not mean you can transfer 11Mbit/s of data over a 802.11b channel, as you have to take overhead into account at the various protocol layers.

I hope this clears up some confusion for you. Also do read the wikipedia page on IEEE 802.11. :)