Adaptive Modulation with Diversity Combining Based on Output-Threshold MRC

In this paper, we propose a combined adaptive modulation transmission and output threshold MRC diversity reception scheme for high spectral and power efficiency wireless transceiver design. The modulation constellation size and the number of combined diversity paths are jointly determined to achieve the highest spectral efficiency but with low combining complexity, given the fading channel conditions and the required error rate performance. We derive the statistics of the resulting output signal-to-noise ratio (SNR) and then use it to analyze the proposed system (i) performance in terms of outage probability and average bit error rate, (ii) complexity in terms of the average number of path estimation and the average number of combined paths, and (iii) spectral efficiency. Some selected numerical examples are finally presented and discussed to illustrate the tradeoff offered by this scheme.