Weighted sum rate maximization for the MIMO X channel through MMSE precoding

Recent results elucidate the optimality of the interference alignment concept in attaining the degrees of freedom of the MIMO X channel. However, in the low-medium SNR regime optimizing the weighted sum-rate seems more meaningful. Since the MIMO X channel subsumes the MIMO interference channel, MIMO multiple access, parallel MIMO point-to-point and MIMO broadcast channel, it is desirable to have a procedure that designs the linear transmitters and receivers in all cases. In this work we have observed that an algorithm based on alternate optimization, along with the proper initialization, is able to provide MMSE precoders attaining the degrees of freedom and significant gains in terms of SNR offset with respect the conventional interference alignment solution.