Resource allocation for QoS multiuser MIMO with zero forcing and MMSE beamforming

To enable ubiquitous end-to-end quality of service over IP networks expanding to rural areas, we examine resource allocation problems of a MAC layer for an OFDM MIMO wireless base station (BS) using multiuser beamforming. We compare two linear beamforming techniques, zero-forcing (ZF-BF) and minimum mean square error (MMSE-BF). To guarantee minimum bandwidth and low packet delay in an environment where the number of users is much larger than the number of BS antennas, one needs to partition the users into several sets and combine space division multiple access (SDMA) with time division multiple access (TDMA). We study the impact on the optimal transmission power resulting from selecting the following design parameters: (i) ZF-BF vs. MMSE-BF; (ii) the number of user sets multiplexed by TDMA; and (iii) the number of BS antennas. Two notable results are observed: (1) power wise, ZF-BF is far more superior to MMSE-ZF; (2) substantial power can be saved by increasing the number of BS antennas; however, only by large increments, e.g., from 6 to 9 and further to 21.