What is CDMA?

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CDMA stands for Code Division Multiple Access. It is a technique used for digital communication, and wireless technology in particular, that involves multiplexing. Whereas conventional communication systems use constant frequencies, CDMA uses multiple access, or multiplexing. Multiplexing, in this case accomplished through the specific type known as spread spectrum, uses varied frequencies to transmit audio signals. This, coupled with code division which requires a certain code to send and receive the frequency, further protects CDMA communications from interference.

Radio systems, one of the earliest forms of telecommunication, required users to have distinct frequencies. Two earlier forms of wireless communication illustrated the limits of methods previous to CDMA. Frequency Division Multiple Access or FDMA only allowed users to operate on a single frequency. For instance, when tuning in to a radio to get sound, a listener must select one frequency or the other. The listener must also tune the frequency to filter out noise in the spectrum that is not associated with one frequency or the other.

The other form of early radio communication was Time Division Multiple Access or TDMA. In this case, users could not share a frequency and each user had to coordinate his or her turn on that frequency in order to communicate. Both FDMA and TDMA posed restrictions for early users, particularly the military. As early as World War II, the military needed to communicate across vast distances that required wireless technology. That was also the case for their adversaries. Military communication units did not have time to wait their turn to transmit sound, or to find a frequency.

Previous telecommunication systems allowed military communication units to transmit sound into the same spectrum their adversaries used. The military’s signals needed a unique identification through a distinct code to avoid interference from enemy communication. The receiver of that message on the other end could similarly retrieve the message based on its unique code in the spectrum.

Just as the radio moved from military use to commercial use, so too was the case with the wireless technology. CDMA became the early choice for personal communication because it could allow multiple users to communicate within the spectrum, avoiding interference or blocking among users. In 1999, CDMA became the standard technology for the telecommunications industry for its growing wireless systems. Since there are large numbers of users in the system communicating at the same time, code division ensures that each user’s signal remains separate in the spectrum.