Statistical suppression of interference with diversity in a mobile-radio environment

In a small-cell mobile-radio system different base stations transmit different signals simultaneously, and at the same carrier frequency, to mobile vehicles in their respective cells. It is desirable that these cochannel stations be placed as close to one another as possible without creating undue interference. However, as a vehicle moves within a cell, both the desired and undesired signals exhibit Rayleigh (local) fading, creating a relatively high probability that the interference exceeds the signal. On the other hand, at the frequencies contemplated it is relatively simple to construct additional antennas that provide independently fading signals, thereby offering the use of diversity techniques. Three different switch diversity techniques are considered, and the improvements produced by each are calculated. It is also shown that some are effective in combating an additional difficulty of the mobile-radio environment; this difficulty is that while the signal received in a moving vehicle is locally Rayleigh, the mean of this Rayleigh process changes slowly with time.