Abstract
In this paper, a composite Rayleigh-Gamma distribution is proposed for the urban wireless channel environment which represents small-scale fading with no Line of sight (LoS) and shadowing. Moment Generation Function (MGF) and truncated MGF for the proposed model are derived. Using these MGFs, the performance of digital communication systems is investigated in terms of channel capacity and bit error rate probability. Results show that the performance is adversely affected by the urban channel environment. Thus, an adaptive M-QAM technique is proposed to enhance the system performance. With the aid of truncated MGF, the performance of adaptive M-QAM system is evaluated in terms of outage probability, system capacity (bit/s/Hz) and average bit error probability. The proposed adaptive technique shows high potential for achieving significant system capacity while maintaining acceptable bit error probability even under severe channel effects.