Relation between Beamforming and Diversity in MIMO System: A Capacity Perspective

In mobile communication, space is a very important domain to use. Two kinds of leading techniques are beamforming and STBC in MIMO system. This paper investigates the relation between beamforming and STBC at the capacity perspective. Both techniques can improve system performance at the cost of the capacity, which shows that they convert the matrix channel into a scalar AWGN channel. At low SNR, the MIMO capacity is less than that of beamforming system, and vive versa in independent MIMO channel. But in highly correlated channel, the capacity of beamforming is larger than that of MIMO system, and MIMO capacity is same with that of STBC. It is proven that beamforming is robust at both independent and correlated channels, and STBC is optimal with respect to capacity when it is code rate one over a channel of rank one. Simulations are conducted at the actual applications.