Demodulation and decoding for diversity mobile radio systems

In mobile communication systems, channel coding and equalisation are required to achieve high-quality signals. The channel degradation owing to multipath fading, time spread and Doppler spread can be further reduced by using diversity techniques, where the receiver is provided with multiple independently faded replicas of the same information signal. The information coming from the diversity channels can be properly combined to improve the system performance. In the paper a new diversity receiver which performs demodulation and decoding of mobile-radio signals is described. The proposed demodulation scheme uses a new distance-combination technique based on the classical MLSE Viterbi algorithm. A new soft-decoding algorithm combining the signals coming from the diversity channels is proposed. The experimental results obtained by computer simulations show a significant improvement of the bit-error rate with respect to hard decoding in return for a modest increase in receiver complexity.