Interference Alignment and Leakage-Based Iterative Coordinated Beam-Forming for Multi-User MIMO in LTE-Advanced

To suppress co-channel interference and achieve good system performance in a Multi-User Multiple Input Multiple Output (MU-MIMO) downlink network, we introduce a novel Interference Alignment (IA) receive matrix design methodology along with a low complexity iterative coordinated beamforming scheme. The introduced scheme takes into account the codebook-based feedback for LTE/LTE-Advanced systems. In our design, IA is utilized to mitigate the inter-cell interference while leakage-based iterative coordinated beamforming is used to combat the intra-cell interference. Optimal transmit beamforming vectors are characterized and a closed-form expression for these beamforming vectors in the presence of quantization error due to the codebook-based feedback is also presented. Simulation is conducted to illustrate the performance of introduced coordinated beamforming strategy. It suggests that for 4 by 2 MIMO systems, rank 2 codebook-based feedback yields much better performance than rank 1 feedback. Furthermore, for a fixed payload size of the codebook, unlike zero-forcing beamforming where the sum throughput is bounded as the signal-to-noise ratio (SNR) increases, in our scheme the performance gap between the rank 2 feedback and perfect feedback remains almost constant as SNR increases.