Impact of correlated diversity branches in Rician fading channels

The effect of correlated branches on the performance of coherent maximum ratio combining (MRC) and non-coherent equal gain combining (EGC) diversity receivers over Rician fading channels is studied. The asymptotic error and outage probabilities for the MRC and EGC receivers with arbitrarily correlated branches for high average signal-to-noise ratios (ASNR) are derived, in terms of the diversity and coding gains. Based on this result, we show that the phase vector φ of the line-of-sight (LOS) components of the channel has a significant impact on the receiver performance in correlated Rician fading channels. The asymptotic upper and lower bounds of the receiver performance as a function of φ are derived. Our results show that with correlated branches the phase vector φ affects the effective Rice K-factor at the diversity receiver output, and hence may result in a coding gain significantly higher than that for independent branches. Further, when the channel correlation matrix is rank deficient and under some additional mild conditions, the receiver performance approaches that in a non-fading additive white Gaussian noise (AWGN) channel.