Optimal Bandwidth Allocation for Source Coding , Channel Coding and Spreading in a CDMA System

This paper investigates the tradeoffs between source coding, channel coding and spreading in a CDMA system, operating under a fixed total bandwidth constraint. We consider a system consisting of a uniform source with a uniform quantizer, a channel coder, an interleaver, and a direct sequence spreading module. The system uses binary phase-shift keyed (BPSK) modulation. Rate-compatible punctured convolutional (RCPC) codes and soft decision Viterbi decoding are used for channel coding. The system is analyzed over both an additive white Gaussian noise (AWGN) channel and a flat Rayleigh fading channel. A tight upper bound for frame error rate is derived for non-terminated convolutional codes. The performance of the system is evaluated using the end-to-end mean squared error (MSE). We show that, for a given bandwidth, an optimal allocation of that bandwidth can be found using the proposed method.