Optimal Power and Modulation Adaptation Policies with Receiver Diversity over Rayleigh Fading Channel

Efficient bandwidth utilization is paramount in wireless communication systems, particulary in fading environments, since fading is one of the major constraints that impair communication in wireless systems. The bandwidth efficiency of a wireless communication system can be enhanced significantly by employing power and modulation adaptation policies with diversity combining gain. In this work, first we examine an analytically-derived solution for Maximum Combining Ratio (MRC) diversity technique for the capacity per unit bandwidth. Then, we design an adaptive transmission system to utilize the diversity combining gain while retaining the target BER by adapting power and constellation size using continuous power, channel inversion with fixed rate and continuous power and disrecte-rate. By considering the effect of diversity combining gain, the designed system yields a reasonable spectral efficiency with respect to target BER that grows as the number of diversity levels increase. Furthermore, the presented results show continuous power and discrete-rate adaptation policy reduces probability of outage unlike its achieved spectral efficiency is close to other selected policies, which ratifies the optimized switching thresholds and makes it best candidate for imperfect channel conditions.