1. A method of MIMO communications in a wireless network, said network having a plurality of wireless units and a plurality of base stations, each base station having one or more transmit antennas, wherein the method comprises the steps of: forming a user group based at least in part on a semi-orthogonal selection of a subset of said plurality of wireless units; and transmitting data over an assigned transmission channel to the wireless units in said user group, wherein the data is transmitted according to a zero-forcing beamforming (ZFBF) operation and at least one designated per-transmit antenna or per-base station transmission power constraint of the base station antennas.