Exact analysis of downlink capacity employing opportunistic feedback and maximal ratio transmission in Rayleigh fading environments

The downlink throughput of opportunistic-feedback multiuser wireless systems with capture effects employing maximal ratio transmission (MRT) in a Rayleigh fading environment is studied. To the best of the authors´ knowledge, MRT has not been employed to improve multiuser system throughput with capture effects. Employing MRT means that the channel fading gains between the base station (BS) and users are a chi-square distribution with 2L degrees of freedom, where L is the diversity order, as opposed to Rayleigh distribution which has been examined in detail in the literature. Thus, the main challenge is to obtain a new and compact channel capacity expression for the system in which the roles of BS and users are reversed to make it practically sound. The new downlink throughput expression is derived as a function of L, fading-gain threshold η, capture ratio z and other parameters. For large η, the capture effects are not as effective as when η is small. Effects of the capture ratio z on system throughput are also obtained. The new findings are validated using available results in the open literature.