Code division multiple access (CDMA)
Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. It should not be confused with the mobile phone standards called cdmaOne and CDMA2000 (which are often referred to as simply CDMA), which use CDMA as an underlying channel access method.
One of the basic concepts in data communication is the idea of allowing several transmitters to send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). This concept is called multiple access. 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 signalling, since the modulated coded signal has a much higher data bandwidth than the data being communicated.
An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. 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 communicate.
CDMA Requirements
Reduction in dropped calls due to handoff failures.
Increase in the coverage of each cell making cell deployment easier and cheaper and subsequently lower maintenance costs.
Increasing the capacity of data communications to enable access to high speed services.
Dramatic improvement in capacity over current systems.
Increase in voce quality and reduction the audible effects of multipath fading
Reduction in the power of handsets which results in smaller more compact handsets with longer battery life and reduces interference with other electronic devices whilst keeping the cost of handset low. This also reduces the fears of health concerns.
