Capacity comparison of multi-element antenna systems

We investigate the capacity of multi-element antenna systems employing three practical techniques, space diversity, spatial multiplexing and beamforming. We compute the capacity of these techniques over flat fading channels. Our results show that the spatial multiplexing works better in omnidirectional environment, or equivalent high-rank channel, while beamforming is fitful for the case of transmit and receive paths being constrained in small angular range, or low-rank channel. Diversity with space-time block coding has similar capacity compared to multiplexing in low-rank channel, but it has capacity loss in high-rank channel due to its transforming the multiple antenna system to single antenna system. Better performance can be obtained by switching the system between different techniques.