Precoding schemes for the MIMO-GBC

The use of M antennas at the base station and of transmitter channel state information can boost the downlink throughput by a factor M (multiplexing gain), even though the receivers have a single antenna and do not cooperate. In this semi-tutorial work, we discuss some low-complexity alternatives to achieve a downlink throughput very close to the optimal sum capacity. We review and compare these alternatives and we show that, in the simple setting of independently fading channels, relatively traditional forms of linear beamforming achieve the best tradeoff between performance and complexity. These results somehow call for a reconsideration of the emphasis that certain recently proposed precoding techniques have enjoyed both in scientific literature and in technology development.