Clustered precoding for coordinated multi-cell systems based on signal-to-leakage ratios

In this paper, we propose a novel clustered linear precoding scheme based on the signal-to-leakage ratio (SLR) maximization applicable to downlink network MIMO. Different from conventional techniques, our proposed scheme is capable of supporting a network configuration in which the number of transmit antennas at the BTSs is smaller than the total number of antennas at all users. To this end, we first provide an insightful connection between the SLR and the total sum-rate. An optimal precoding scheme that maximizes the SLR for a given input covariance matrix is then developed. Asymptotically, the precoders obtained based on the SLR criterion also lead to the maximum sum-rate. By further assuming per-BTS power constraints (PBPCs), optimal power allocation schemes are developed to optimize the sum-rate for users with single receive antenna. Numerical results show that the proposed method outperforms the conventional schemes based on SLR. The gain is observed in terms of both the sum-rate and the bit error rate (BER) performance.