Code Division Multiple Access (CDMA) is a spread-spectrum multiple-access technique, within the domain of wireless communications and digital signal processing, in which pseudorandom code sequences are used both to convert analog signals to digital form and to separate simultaneous users sharing the same frequency band into distinct "code channels," rather than dividing access by frequency (FDMA) or time (TDMA). The scheme relies on two classes of spreading codes with complementary roles: orthogonal codes (e.g., Walsh codes) for channelization on the forward link, where near-zero cross-correlation and strong autocorrelation allow a receiver to isolate one user's signal from co-channel interference, and pseudorandom noise (PN) codes for the reverse link, which provide code-division separation, security, and timing acquisition. This is complemented by channel-coding theory (convolutional and block/cyclic codes, interleaving) that provides error protection and burst-error mitigation over hostile fading channels, and by call-processing state machines (initialization, idle, access, traffic) that govern how a mobile station acquires, synchronizes with, and negotiates code and power resources with a base station.
Code Division Multiple Access (CDMA) is a spread-spectrum multiple-access technique, within the domain of wireless communications and digital signal processing, in which pseudorandom code sequences a…