Effect of correlation in diversity systems with Rayleigh fading, shadowing, and power capture

With the growth of wireless personal communications networks and wireless local area networks (WLAN's), the need for increased reliability of the radio link has become evident. The use of diversity techniques, such as dual receiving antennas, helps mitigate the effect of multipath fading in both the in-building and land mobile radio environments. A significant issue in the design of such systems is the degree to which correlation between the two or more diversity signals can be tolerated. In this paper, we consider the use of diversity techniques in radio systems that are subject to correlation. Rayleigh fading, lognormal shadowing, and the radio capture effect. In the presence of two simultaneously transmitting stations, the throughput, conditioned on the local-mean power, is determined exactly for the case of a dual diversity receiving station. The insight gained from the two-station analysis is used to develop an accurate approximation for cases with more than two stations. The degree to which correlation can be tolerated without significant performance loss relative to the case of independent diversity signals is quantified, as are the effects of different system parameters (i.e., the capture ratio, power roll-off coefficient, and the amount of shadowing). Furthermore, the relationship between the envelope and power correlation coefficients is presented. An application of the capture results to the slotted ALOHA protocol is also included.