Impact of fading correlation and unequal branch gains on the capacity of diversity systems

We investigate the effect of fading correlation and branch gain imbalance on the Shannon capacity of diversity systems in conjunction with adaptive transmission techniques. This capacity provides the theoretical upper bound for the spectral efficiency of adaptive transmission schemes. We obtain closed-form expressions for this capacity for Rayleigh fading channels under four adaptation policies: optimal power and rate adaptation (OPRA), optimal rate adaptation with constant power (ORA), truncated channel inversion with fixed rate (TIFR), and complete channel inversion with fixed rate (CIFR). We give numerical examples illustrating the main trends and offer comparisons on the behavior of OPRA, ERA, TIFR, and CIFR under variation of different parameters