Spatial correlation in ultrawideband channels

Correlated fading adversely affects the spatial multiplexing and diversity performance of multiple-antenna systems. This paper presents an empirical investigation of spatial correlation in ultrawideband (UWB) indoor channels in the FCC- allocated 3.1-10.6 GHz band. The impact of a number of system parameters on spatial correlation at the receiver is evaluated. It is found that the coherence distance falls with channel bandwidth in endfire arrays but not in broadside arrays. The complex correlation decays less rapidly with distance in broadside arrays than in endfire arrays, especially under line-of-sight, but the envelope correlation is circularly symmetric in space. Strong dependence of spatial correlation and coherence distance on the channel center frequency is observed. Furthermore, horizontally polarized links are found to exhibit less correlation than vertically polarized links. A discussion of the implications of these results for multiple-antenna UWB systems is provided.