Multi-Keyholes and Measure of Correlation in MIMO Channels

Abstract

Keyhole MIMO channels were predicted theoretically and also observed experimentally. However, they are not often encountered in practice since the assumption of a single propagation eigenmode is only a rough approximation of real propagation environments. This paper presents an extension to the single-keyhole channel model, termed a channel, which includes a number of statistically independent keyholes. Correlated full-rank and rank-deficient multi-keyhole channels are considered in detail. Under some general conditions the full-rank multi-keyhole channel is asymptotically Rayleigh fading if the number of keyholes is large. When the number of both Tx and Rx antennas is large, the capacity of a rank-deficient multi-keyhole channel is a sum of the capacities of the equivalent single-keyhole channels. The outage capacity distribution of both full-rank and rank-deficient multi-keyhole channels is asymptotically Gaussian. Based on the asymptotic capacity analysis, full ordering scalar measures of MIMO channel correlation and power imbalance are introduced