Distributed Spatial-Temporal Precoding and Power Allocation in MIMO Relay Systems with Limited Feedback

Due to similarity between cooperative systems and traditional multi-input-multi-output (MIMO) systems, precoding techniques can be introduced into MIMO relay systems. In this paper, a practical distributed precoding scheme with limited feedback scheme is proposed in the MIMO relay system, where the zero-forcing (ZF) relaying protocol is proposed to be used in the relay node so that the information of relaying channel and noise can be compressed into two positive real coefficients. Precoding is proposed to be operated through two continuous transmitted vectors of the source node, which is termed as distributed spatial-temporal precoding (DSTP). Power allocation is combined with the proposed DSTP for higher spectrum efficiency. DSTP outperforms the direct transmission and the simple ZF relaying protocol. Analysis and numerical results demonstrate that DSTP with suitable receiver performs very close to the capacity low bound of the ZF relaying system.