Code Division Multiplexing

Code Division Multiplexing (CDM) is a technique in which each channel transmits its bits as a coded channel-specific sequence of pulses. This coded transmission typically is accomplished by transmitting a unique time-dependent series of short pulses, which are placed within chip times within the larger bit time. All channels, each with a different code, can be transmitted on the same fiber and asynchronously demultiplexed. Other widely used multiple access techniques are Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA).

Code Division Multiplex techniques are used as an access technology, namely Code Division Multiple Access (CDMA), in Universal Mobile Telecommunications System (UMTS) standard for the third generation (3G) mobile communication identified by the ITU. Another important application of the CDMA is the Global Positioning System (GPS).

However, the term Code Division Multiple access (CDMA) is also widely used to refer to a group of specific implementations of CDMA defined by Qualcomm for use in digital cellular telephony, which include IS-95 and IS-2000. The two different uses of this term can be confusing. Actually, CDMA (the Qualcomm standard) and UMTS have been competing for adoption in many markets.