Zero-forcing vs unitary beamforming in multiuser MIMO systems with limited feedback

We consider a multiuser MIMO downlink system with multiple antenna mobile terminals where channel state information at the base station is provided through limited uplink feedback. In a multi-cell environment we compare two transceiver architectures based on zero forcing and unitary beamforming respectively. For both schemes we show how the additional degrees of freedom provided by multiple receive antennas can be exploited to improve system performance, by a proper design of the receive combiner. We propose channel quantization solutions that adapt to the transceiver architectures and exploit MIMO channel statistic. Numerical simulations validate the effectiveness of the proposals in a multi-cell environment where long-term proportional fairness is guaranteed among the users in the network.