System performance of a three cell network with corner users using precoding, interference alignment and quantized limited channel feedback

The users in the common corner of a three-cell downlink multi-user MIMO system suffer from low signal strength from its own cell as well as equal strength interference signal from its neighbour two cells. To improve system sum-rate performance in such scenario, schemes for interference mitigation is adopted. Further, the full CSI feedback by the users to its base station puts high burden on the reverse feedback channel. Quantized reduced channel information feedback with interference alignment technique and suitable precoding can reduce the burden on the reverse channel as well as can improve the system sum-rates. LTE code book based precoding techniques provide improvements in the sum-rate. We design precoding using singular value decomposition (SVD) on selected code vectors based on maximization of Equivalent Channel-Code vector (SVD_ECC), and maximization of SINR-Code vector (SVD_SINRC). Both these techniques show system sum-rate improvement over ZF based precoding technique, SVD_ECC providing more improvements than SVD_SINRC. We also experimented with users with orthogonal equivalent channels and the subsequent SVD on the selected users channel (SVD-ORTHO).  We show results varying user SNR, number of selected user K and the total number of active user L in a cell.