On the Maximum Useful Number of Receiver Antennas for MRC Diversity in Cochannel Interference and Noise

The effect of noise on the maximum useful number of receiver antennas that can be deployed in a cochannel interference diversity system is examined. The long term signal- power-to-interference-plus-noise-power ratio (SINRP), the long term signal amplitude to the square root of interference plus noise power ratio (SAINPR), the average instantaneous signal-to- interference-plus-noise ratio (AISINR), and the average bit error rate (BER) of a maximal ratio combining (MRC) diversity system in the presence of multiple cochannel interferers and additive white Gaussian noise (AWGN) are evaluated when the desired user signal and the interfering user signals are independent, and each of them experiences correlated Ricean fading at the receiver antennas. The results show that a previous design rule which states that the performance of a fixed-size antenna array containing the maximum number of independent antennas cannot be significantly improved by adding more than one additional antenna, still applies when the interference dominates the noise. It is shown that the SINRP and SAINPR measures exhibit asymptotic limits as the number of correlated antennas increases. Simple expressions for these limits are derived and it is shown that these asymptotic limits are unchanged when noise is neglected.