Code-division multiple access

Code-division multiple access (CDMA), also known as "spread spectrum", is a form of where the transmitter encodes the signal using a  which the receiver also knows and can use to decode the received signal. Each different random sequence corresponds to a different communication channel.

History
pioneered the introduction of CDMA in wireless 2G telephone services. Motorola used CDMA for their digital mobile phones. Verizon and adopted  for their respective 3G networks. The version of the iPhone 4 released through Verizon was the first mobile device from Apple to support CDMA.

Retirement of 3G service
Verizon is scheduled to shut down its CDMA-based 3G network on December 31, 2022 to make room for more advanced wireless services. T-Mobile shut down 's old CDMA network on March 31, 2022. This affects all older iPhone models that do not support (iPhone 5C, 5S and earlier). This also affects the CDMA version of the iPad 2.