IEEE 802.11. This standard specifies a 2.4 GHz operating frequency with data rates of 1 and 2 Mbps using either direct sequence (DSSS) or frequency hopping spread spectrum (FHSS). IEEE 802.11b data is encoded using DSSS (Direct Sequence Spread Spectrum) technology. DSSS works by taking a data stream of zeros and ones and modulating it with a second pattern, the chipping sequence.
In 802.11, that sequence is known as the Barker code, which is an 11-bit sequence (10110111000) that has certain mathematical properties making it ideal for modulating radio waves. The basic data stream is XOR’d with the Barker code to generate a series of data objects called chips. Each bit is "encoded" by the 11 bit Barker code, and each group of 11 chips encodes one bit of data.
Rather than using the Barker code, IEEE 802.11b uses CCK (Complementary Code Keying) to achieve 11 Mbps. CCK uses a series of codes called Complementary Sequences. Because there are 64 unique code words that can be used to encode the signal, up to 6 bits can be represented by any one particular code word (instead of the 1 bit represented by a Barker symbol).
The CCK code word is modulated with the QPSK technology used in 2 Mbps wireless DSSS radios. This allows for an additional 2 bits of information to be encoded in each symbol. Eight chips are sent for each 6 bits, but each symbol encodes 8 bits because of the QPSK modulation. The spectrum math for 1 Mbps transmission works out as 11 Mchips per second times 2 MHz equals 22 MHz of spectrum. Likewise, at 2 Mbps, 2 bits per symbol are modulated with QPSK, 11 Mchips per second, and thus have 22 MHz of spectrum. To send 11 Mbps 22MHz of frequency spectrum is needed.