ANALYSIS AND PERFORMANCE OF BIDIRECTIONAL DECODING OF CONVOLUTIONAL-CODES OVER FADING CHANNELS

In this paper, the performance of suboptimal convolutional decoding ov er fading channels is explored. The suboptimal decoding algorithm used is the bidirectional algorithm. By estimating a ''decoder weight spec trum'' for the decoder, an ''equivalent free distance'' may be observe d. Furthermore, by using this ''decoder weight spectrum,'' useful esti mations of the error probabilities are obtained and compared to comput er-simulation results in the case of very slow and very fast fading. T he resultant curves are shown to be very tightly related. Computer-sim ulation results are also shown for various signal-to-noise ratios, nor malized Doppler spreads, and frame length on three typical fading chan nels: the Rayleigh fading channel with exponential and Bessel autocorr elation functions and the Rician fading channel with exponential autoc orrelation function, We show that considerable gains (up to 4 dB) can be obtained with respect to a similar-complexity Viterbi decoder at a frame error probability P-e = 10(-3) and a slightly smaller gain (up t o 1.8 dB) at a bit error probability P-b = 10(-5).