Code
division multiple access (CDMA) describes a communication
channel access principle that employs spread-spectrum technology and a special
coding scheme (where each transmitter is assigned a code). In communications
technology, there are only three domains that can allow multiplexing to be
implemented for more efficient use of the available channel bandwidth and these
domains are known as time,
frequency and space. CDMA divides the access in
signal space. By contrast, time division multiple access (TDMA) divides
access by time, while frequency-division multiple access (FDMA) divides
it by frequency. CDMA is a form of "spread-spectrum" signaling, since
the modulated coded signal has a much higher bandwidth than the data being
communicated.
An analogy to the problem of multiple access is a room (channel) in which
people wish to communicate with each other. To avoid confusion, people could
take turns speaking (time division),
speak at different pitches (frequency
division), or speak in different directions (spatial division). In CDMA, they
would speak different languages. People speaking the same language can
understand each other, but not other people. Similarly, in radio CDMA, each
group of users is given a shared code. Many codes occupy the same channel, but
only users associated with a particular
Code can understand each other.
CDMA is also the current name for the cellular technology originally known
as IS-95. Developed by Qualcomm and enhanced by Ericsson, CDMA is characterized
by high capacity and small cell radius.CDMA also refers to digital cellular
telephony systems that use this multiple access scheme, as pioneered by QUALCOMM,
and W-CDMA by the International Telecommunication Union (ITU), which is used in
GSM’s MTS.CDMA has been used in many communications and navigation systems,
including the Global Positioning System and the OmniTRACS satellite system for
transportation logistics.
More abstracts about the CDMA-Code division multiple access