Code-division multiple access

Code-division multiple access (CDMA) lets multiple users transmit over the same frequency band at the same time by assigning each a distinct spreading code.

Direct-sequence spread spectrum: A spread-spectrum technique that multiplies data by a faster pseudorandom chip sequence. CDMA commonly spreads each user's signal with a distinct chip sequence.
Multiple access: A set of methods that lets multiple users share a communications medium. CDMA is one way to allocate a common channel among simultaneous users.
IS-95: A second-generation digital cellular standard that uses code-division multiple access. IS-95 was an early commercial cellular system built around CDMA.
Frequency-division multiple access: A channel-access method that assigns different frequency bands to different users. Unlike CDMA, FDMA separates users primarily by frequency allocation.
Pseudorandom noise code: A deterministic sequence with noise-like statistical properties, used in communications for spreading and identification. A receiver uses assigned code sequences to recover a user's spread signal.
Spread spectrum: A communications approach that distributes a signal across a bandwidth wider than its information requires. CDMA draws on spread-spectrum signaling to make users separable by code.
CDMA2000: A family of third-generation mobile standards developed as an evolution of IS-95. It extended CDMA cellular technology to higher-rate data services.
Time-division multiple access: A channel-access method that assigns different time slots to different users. TDMA separates transmissions in time rather than by spreading code.
Code correlation: A measure of similarity between two sequences as one is shifted relative to the other. Low cross-correlation helps a receiver distinguish users sharing the same band.
Chip (communications): A unit of a spreading sequence, typically transmitted faster than the data symbols it represents. The chip rate determines how broadly a CDMA signal is spread.

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