CDMA - definition

CDMA (code division multiple access) is a multiple access technique in which multiple signals can be transmitted simultaneously in the same frequency band through the use of unique spreading codes. Unlike other multiple access methods, such as TDMA (time division multiple access) or FDMA (frequency division multiple access), in CDMA each user is assigned an individual sequence code, which allows the transmitted data to be distinguished even when overlapping in time and space.

The technology is based on a spread spectrum (spread spectrum) technique in which the signal is transmitted using a wide bandwidth, much wider than its information content requires. Spreading is done by multiplying the user's signal by a pseudo-random sequence, a so-called spreading code. A receiver knowing the same code is able to effectively recover the original signal, ignoring the Others transmissions as noise. In this way, it is possible for multiple independent data streams to coexist in the same frequency range.

CDMA has found widespread use in second- and third-generation mobile phone systems (e.g. IS-95, cdmaOne, CDMA2000), as well as in satellite communications and military systems. Due to its high immunity to interference, efficient use of spectrum and good transmission quality at low signal power levels, this method was particularly valued in high user density environments.

From a technical point of view, CDMA implementation requires precise synchronisation timing and the use of advanced decoding algorithms to distinguish and reconstruct the relevant signals from among overlapping transmissions. In practice, a key element of CDMA operation is the so-called correlation detector, which recognises a given user code and separates its signal from the others.

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