There now appears little doubt that spread spectrum technologies will dominate wireless communications networks in the future. Already, the code division multiple access system pioneered by Qualcomm, and commonly known as CDMAOne, is the digital air interface standard embraced by the largest US network operator. While functionally dissimilar, both of the dominant standards embraced worldwide for so-called third generation wireless systems are also based on CDMA spread spectrum.

All CDMA systems used in public wireless communications networks share a few common traits, among which is common radio channel operation. That means that the same radio channel is used in each base station and sector of the network. To meet capacity requirements a network may employ multiple CDMA RF channels, but to a great extent each operates independently, and calls in progress are rarely moved from one to another. Within the RF channel, different traffic channels are separated by the different orthogonal Walsh codes used for digitally mixing, or "spreading", each traffic data stream. At any moment during a call, the sector transmitting the signal intended for a mobile will be the one that provides the strongest signal (as received by the mobile). When a mobile is in a position where it receives signals from two or more sectors at roughly the same level they will all simultaneously transmit the signal for that mobile, a process called soft handoff. In the course of a call, as a mobile moves through the coverages of different sectors the "active list" of sectors involved in the call (i.e. transmitting to the mobile) will change, with at least one sector the one providing the strongest signal at any point in time always included.

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Credit: Wireless Design & Development