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CDMA
Posted Date: 18 Feb 2008 Resource Type: Articles/Knowledge Sharing Category: Education
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Posted By: Moncy Member Level: Silver
Rating:  Points: 1
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Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with cdmaOne (often referred to as simply "CDMA"), which is a mobile phone standard that uses CDMA as its underlying channel access method.
CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. 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 has been used in many communications and navigation systems, including the Global Positioning System and the OmniTRACS satellite system for transportation logistics.
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