What is code division multiplexing?
Code division multiplexing (CDM) is a networking technique in which several data signals are combined for simultaneous transmission over a common frequency band.
When CDM is used to allow multiple users to share a single communication channel, the technology is called CDMA (Code Division Multiple Access).
CDMA uses spread spectrum, a technology developed during World War II, to prevent adversaries from intercepting and blocking transmissions. In the spread spectrum, a data signal is sent over a range of frequencies in an assigned frequency spectrum.
A pseudo random spreading code is used to multiplex the basic signal. Multiplexing with a spreading code increases the bandwidth required for the signal and spreads it over the available spectrum. The receiving device knows the spreading code and uses it to demultiplex the signal.
CDMA offers some built-in security as the transmissions of several users are mixed within the frequency spectrum. The spreading code is required to decode a specific transmission.
Different variants of CDM and CDMA are used in 2G and in subsequent generations of cell phone technology.