Cochannel interference rejection in a mobile radio space diversity system

Diversity is often used in radio systems to alleviate the problem of fading. It is shown here that the use of diversity in a mobile radio system also will result in better utilization of the frequency spectrum. In a system which reuses channels in physically separated areas, probability distributions of signal-to-cochannel interference ratios in 1-, 2-, and 4-branch diversity systems are developed by Monte Carlo methods. We consider two cases: first, we assume signal strength to be Rayleigh distributed, which is a valid model for reception within a small localized area; second, we take shadow losses into account by assuming a more realistic long-term fading model. The effect of using diversity in a mobile radio system is considerable with either model. Assuming a hexagonal cell pattern of frequency reuse, it is shown that frequencies may be reassigned more often in a diversity system than in a system which does not use diversity. The conclusion, therefore, is that a diversity system utilizes the frequency spectrum more efficiently than an equivalent nondiversity system.