Overview
CDMA (Code Division Multiple Access) has altered the face of cellular communication ever since it has debuted in 1995. Its arrival heralded the arrival of highly efficient networks with higher user capacities and better voice quality, among a host of other features. Today, it is a key enabling technology for the transition to not only 3G, but even possibly 4G.

What is CDMA?
Code Division Multiple Access (or CDMA) is a spread spectrum carrier access technique in which the original data signal is spread over a large frequency range, with the help of a pseudo-random spreading signal. This spreading technique imparts CDMA with a great deal of resistance to multipath fading, as the signal occupies the entire bandwidth. This is not the case in TDMA and FDMA technologies, wherein each user signal is allocated a small fragment of the entire bandwidth. CDMA manages to allocate each user with the entire channel bandwidth by using a special code (the pseudo random spreading signal), due to which, to a receiver locked on to one signal, all other signals appear as noise.

IS-95 CDMA standards
The first CDMA standard used widely in the digital cellular area is the IS-95 CDMA standard, which is also sometimes called as cdmaOne. CdmaOne, however, covers a family of IS-95 (IS-95A and IS-95B) standards which provide services for PCS and WLL over and above cellular services. IS-95A is the older 2G standard, which was revised to get the IS-95B standard, which is considered as a 2.5G technology.

IS-95 CDMA specifications
Mobile Frequency Range          Rx: 869-894; Tx: 824-849 MHz
Number of Channels               20 (798 users per channel)
Channel Spacing                    1250 kHz
Modulation                             QPSK/OQPSK
Channel Bit Rate                    1.2288Mb
CdmaOne currently has over 100 million users worldwide, but as the market shifts towards 3G technologies, it is likely to be replaced by CDMA2000.
For further information visit www.cdg.org (CDMA Development Group)