grouped into 6-bit symbols and each 6-bit symbol is mapped to one of the 64 codes. When the receiver demodulates the symbol bit stream, the 8 bits received should be one of the 64 8-bit code sequences which correspond to one of the 6-bit input data symbols. This is described as complementary code keying and is a good example of the use of sequency in the encode-decode process. There is technically no spreading gain with this arrangement, though there is some (modest) coding gain due to the equality of distance between each of the 64 codes. The occupied bandwidth remains at 22 MHz. The difficulty then arises as to how to manage higher user data rates. The answer with 802.11 b is to use an OFDM multiplex. 3.3.4 Walsh Codes used in IS95 CDMA/1EX EV Present-generation wide-area cellular CDMA systems have to date not needed to support the higher data rates expected in local area systems, and for that reason have not to date needed to use an OFDM multiplex. Code multiplexing and channel coding were therefore chosen to provide an acceptable compromise between implementation complexity and performance. IS95 CDMA, the precursor of the CDMA2000 and 1XEV/DO system in use today, uses a 64 by 64 Hadamard matrix. This consists of 64 codes of length 64 of which code 0 is made up of all 1s and is used as a pilot and code 32 is made up of alternating 1s and Os and is used for synchronisation. The other codes have their Os and 1s, or rather - -1s and +1s, arranged SO that each of the codes is orthogonal to each other. Orthogonal in this context means that the codes are equally distinct from one another, or in other words do not interfere with each other as a product of the (FHT) transformation process. These codes are often referred to as Interrelationship of the Physical Layer with Other Layers of the OSI Model Walsh codes (named after Joseph Walsh) but are in practice based on the Hadamard matrix. Each code has 32 places where it is different from other codes. In other words each code has a Hamming distance of 32 from other code