Gallager codes for CDMA applications. II. Implementations, complexity, and system capacity

We focus our attention on Gallager codes with parameters compatible with the IS-95 cellular radio standard. We discuss low complexity software and hardware implementations of an iterative decoder for {N,-,3} Gallager codes. We estimate that by using Gallager codes, a factor of five improvement in the code-division multiple-access system capacity relative to an uncoded system can be achieved, equivalent to a factor of two improvement relative to state-of-the art orthogonal convolutional codes. Simulation results demonstrate the good performance of short-frame Gallager codes in the additive white Gaussian noise and certain fading channels.