Code Division Multiple Access (CDMA) is an over-the-air access and multiplexing technology for digital cellular systems.
CDMA is distinctly different from Frequency Division Multiple Access (FDMA) or Time-Division Multiple Access (TDMA) technology. It does not assign a unique frequency to each user. Instead, each transmitting signal (voice or data) uses the full available spectrum. Individual conversations are assigned a unique code in the CDMA spectrum. Therefore, conversations use the full bandwidth simultaneously, enabling more users to communicate on the same network at the same time. Notice that this concept is quite different from the other two main access technologies (FDMA and TDMA) where each user is assigned a specific frequency range or slot.
In the last two decades, it has been used mainly for second-generation (2G), and, more recently, in third-generation (3G), mobile technology. However, it was first used in World War II to jam reception of transmitting signals making voice reception extremely difficult. In order to receive voice properly, the receiver must be able to decode the receiving signal with a pseudo-noise (PN) sequence specific to the user.
During World War II, the technology behind CDMA was classified. However, Qualcomm, an American-based company, is able to commercialise the technology and use it for cellular technology successfully. Qualcomm also holds the relevant patents for CDMA. Qualcomm designed and developed the basic building blocks of this technology by creating the communications chip for CDMA. CDMA provides several benefits such as capacity increase, secured communication, and immune-to-wireless environment.
CDMA has been used in IS-95 and 1xRTT and other subsequent cellular standards. Download rates available to CDMA users vary by standard but range from 16.67 Mbps to 28 Mbps.
CDMA is generally used in North America and some parts of Asia.