Effect on capacity of clustering in indoor MIMO channels

Abstract

Published experimental results suggest that in indoor environments multipath rays arrive in clusters. The clusters arrive with a uniform probability density in azimuth angle, whilst rays within a cluster arrive with a Laplacian probability density with angular spread σ. Using Monte Carlo type simulations, assuming 'narrowband' channel conditions and 'single bounce' scattering between TX and RX, we make comparisons between the MIMO capacity of Rayleigh matrix channels with independent elements and matrix channels constructed using this clustering model. We confirm, as intuition would expect, that in general clustering of rays leads to a decrease in capacity, due to increased spatial correlation across a MIMO array. In addition, we find that the MIMO channel capacity can also increase as the number of scatterers increases through scatterer redundancy or diversity. Further, we look at the growth of capacity with n the minimum of the number of antennas at TX and RX; for independent Rayleigh matrix channels this growth is known to be linear offering the possibility of unprecedented spectral efficiencies as n increases. However, taking published results at 7 GHz that suggest an angular spread σ ≈ 25°, we find that the growth of capacity with n, although no longer linear, is still significant compared to optimal RX diversity with maximal ratio combining. (7 pages)