DEMODULATION AND DECODING FOR DIVERSITY MOBILE RADIO SYSTEMS

In mobile communication systems, channel coding and equalisation are r equired to achieve high-quality signals. The channel degradation owing to multipath fading, time spread and Doppler spread can be further re duced by using diversity techniques, where the receiver is provided wi th multiple independently faded replicas of the same information signa l. The information coming from the diversity channels can be properly combined to improve the system performance. In the paper a new diversi ty receiver which performs demodulation and decoding of mobile-radio s ignals is described. The proposed demodulation scheme uses a new dista nce-combination technique based on the classical MLSE Viterbi algorith m. 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 r ate with respect to hard decoding in return for a modest increase in r eceiver complexity.