Mixed Transmission for MIMO Relay Channels with Limited Feedback Precoding

A novel transmission scheme that mixes half-duplex decode-and-forward cooperative relay transmission (RT) with direct transmission (DT) is proposed for multiple-input multiple-output (MIMO) relay channels. To support limited feedback precoding for DT and RT, a precoder codebook is presented where each codeword can be transformed into a new codeword of different dimension. This allows varying number of spatial substreams and resource allocation. Simulation results show significant average capacity gains of the proposed scheme over pure DT scheme and pure RT scheme.