Channel coding for narrow-band Rayleigh fading with robustness against changes in Doppler spread

For digital transmission over frequency-nonselective fading channels, data security can be obtained by error correction coding, but the coding scheme has to be adapted to the channel properties. For many vehicular applications, the range of possible vehicle speeds is large and in the UHF band the resulting Doppler frequency may not be small relative to the symbol rate-suggesting a differential detection scheme. Therefore, the channel coding should be robust against changes in Doppler spread. A combination of a convolutional code (soft-decision decoding) and a Reed-Solomon (RS) code is considered, and the performance in a narrow-band Rayleigh-fading channel with differential quaternary phase shift keying (DQPSK) modulation without interleaving is evaluated as a function of signal-to-noise ratio (SNR) and Doppler spread by computer simulations. This transmission scheme is proved to have good performance over a large variety of vehicle speeds.