Outage Probability of Impairments Due to Combining Errors in Rayleigh Fading Channels Incorporating Diversity

The principles of diversity combining have been known to the wireless communication fraternity for decades. Diversity requires that a number of transmission paths be available, all carrying the same message but having independent fading statistics. The mean signal strengths of the paths should also be approximately the same. Proper combination of the signals from these transmission paths yields a resultant with greatly reduced severity of fading, and correspondingly improved reliability of transmission. Space diversity is a historical technique that has found many applications over the years and is in wide use in a variety of present-day microwave systems. It is relatively simpler to implement, and does not require additional frequency spectrum. Each of the M antennas in the diversity array provides an independent signal to an M-branch diversity combiner, which then operates on the assembly of signals to produce the most favorable result. A variety of techniques are available to perform the combining process in a fading channel like Rayleigh channel. Maximal Ratio Combining (MRC) is considered as the most efficient among all techniques as it improves the average Signal-to-Noise Ratio (SNR) over that of a single branch in proportion to the number of diversity branches combined, and also provides lowest probability of deep fades.