LTE Codebook Capacity Loss for Single-Cell Multi-User MIMO Channels

Multi-user downlink MIMO communication has the potential to increase throughput using efficient beamforming. However, the precoding criteria assume perfect knowledge of the beamforming matrices at the base station (BS). This requires a user to transmit its complete channel information to the BS, a task that entails significant overhead. Limited feedback precoding, a part of LTE standardization now, needs only limited information be fed back to the BS. This paper studies the capacity loss incurred by using LTE codebooks, under different power allocation schemes with varying degrees of optimality. The sub-optimal power allocation schemes also ensure a better throughput-fairness trade-off. It is observed that using LTE codebooks results in a significant loss and that there is a need to develop codebooks which offer better adaptation to channel variations.