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What is CDMA mobile?

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11/07/2009

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Code division multiple access (CDMA) is the current name for the cellular technology originally known as IS-95. This technology is in competition with the GSM technology set for leadership in the global cellular technology market. Developed originally by Qualcomm and enhanced by Ericsson, CDMA is characterized by its high capacity and small cell radius, employing spread-spectrum technology and a special coding scheme (using which each transmitter is assigned a code). By contrast, time division multiple access divides access by time, while frequency-division multiple access 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 also refers to digital cellular telephony systems that use this multiple access scheme, such as those pioneered by QUALCOMM, and W-CDMA by the International Telecommunication Union (ITU).
CDMA has been used in many communications and navigation systems, including the Global Positioning System and in the OmniTRACS satellite system for transportation logistics.