Measurements on the Impact of Sparse Multipath Components on the LOS MIMO Channel Capacity

The channel capacity of indoor line-of-sight MIMO channels is affected by the geometrical antenna setup. In theory there exist rules for the design of LOS channels with optimum channel eigenvalue profile providing maximum capacity. These prescripts are only valid in the absence of multipath signals. By measurements we investigate the relevance of such design rules in real-world MIMO channels consisting of a LOS signal component as well as multipath parts. For that purpose two new performance measures are introduced and shown to be very adequate to distinguish capacity variations which are caused by changes in receive power from those that are caused by differing eigenvalue profiles of the channel matrix. Even sparse multipath signals turn out to be capable of distinctly enhancing the measured spectral efficiency in low-rank channels, while for the high-rank case any multipath components get almost negligible. More important, the geometrical antenna setup not only affects the LOS signal, but also the remaining signal parts. Moreover, the angles of arrival determine, how multipath components affect the LOS channel capacity.