Error performance improvement of QDPSK in the presence of cochannel or multipath interference using diversity

Abstract

AbstractThe quadriphase PSK system is thought to show the highest spectrum efficiency among M‐ary PSK systems for mobile communication purposes and is a noted digital radio system. the diversity effect of the QDPSK system using differential detection has been analyzed approximately. However, since no exact analysis has been done, approximation accuracy has not been clarified. This paper first compares the exact analytical value under cochannel interference and the approximate formula. As a result, it is shown by the method of least squares that the error rate is approximated very closely in precision with a simple formula. Analysis of multipath interference, which simulates frequency selective fading, is carried and the performance difference from that under cochannel interference is discussed. the diversity effect for multipath interference is lessened slightly compared with cochannel interference. It is also indicated that when the average power of a first‐coming wave is nearly equal to that of a delaying wave (often the case in multipath interference) and the error rate is degraded, the diversity effect cannot be expected practically. Finally, the need for a technique to alleviate degradation caused by this difficult‐to‐control propagation characteristic is mentioned.