Fixed-point performance of space-time turbo trellis codes on fast fading channels

To improve the performance of wireless communication systems, bandwidth efficient space-time turbo trellis codes (ST Turbo TC), which is based on the turbo structure, has been proposed in the literature. In this paper, we analyze the performance of a fixed-point ST Turbo TC decoder using sliding window algorithm. In particular, we present the investigation of bit-width optimization for a 4-state QPSK ST Turbo TC decoder based on the symbol-by-symbol (SBS) logarithm-maximum a posteriori (Log-MAP) algorithm on fast fading channels. The decoder structure utilizes a sliding window algorithm for reducing memory requirements and decoding delay. We show that ST Turbo TC is feasible for finite word length representation without significant degradation in the frame error rate (FER) performance. Through computer simulation, the optimum word length configurations are determined for all quantities external and internal to the ST Turbo TC decoder.