Impact of Mobile Antenna Mismatch on Receive Antenna Diversity in Frequency-Flat Rayleigh Fading Channels

Receive antenna diversity is a technique that uses multiple antennas at the receiver side to improve signal reception performance by exploiting spatial diversity. However, in a mobile diversity receiver, the diversity performance is degraded by mobile antenna mismatch created by, e.g., body and hand effects. In this paper, we first explain the mechanism of antenna mismatch and then derive analytic results on the distribution and mean value of the combined SNR in a general frequency-flat Rayleigh fading environment. Three combing techniques are considered: MRC (maximal ratio combing), EGC (equal gain combing) and SC (selection combing). We also present simulated results on BER performance showing that, in a mobile terminal with two receive antennas, single mobile antenna mismatch up to -7 dB causes considerable degradation in array gain, but only negligible reduction in diversity order such that the diversity system still exhibits significant improvement in BER performance compared to an ideal single receive antenna system. Even when both antennas have a mismatch up to -7 dB, the diversity system shows noticeable improvement in BER performance at high SNR.