Joint MMSE precoding & detection for interference alignment in MIMO X channels

In this paper, precoding and receive filter matrices are designed such that minimum mean square error (MMSE) is achieved for interference alignment using 3-symbol extension in the multiple-input multiple-output (MIMO) X channels which comprise two transmitter-receiver pairs with M antennas at each transmitter/receiver. The performance of the proposed algorithm is demonstrated through numerical simulation and compared with the conventional scheme where the precoding matrices are randomly generated and the respective linear equalizers are employed at the receivers. The bit-error-rate (BER) performance of the proposed algorithm is superior compared with that of the conventional scheme across all signal-to-noise ratio (SNRs). Its BER improves with the iterative procedure to refine the precoding and receive filter matrices. Moreover, only a small number of iterations is required to achieve significant improvement in the BER performance.