Downlink multi-user interference alignment in two-cell scenario

In this paper, the problem of Downlink Multi-User MIMO (DL MU-MIMO) transmission from two interfering transmitters, each equipped with M antennas to multiple users each equipped with K antennas is considered. It is assumed that all users receive a single data stream of rank one from only one of the transmitters. A novel transmission/reception scheme is proposed based on the idea of Interference Alignment (IA), which aligns the interference coming from each transmitter to the users in the other cell along a single predetermined vector vref, and hence, leaves more degrees of freedom for signal transmission from each transmitter. Furthermore, unlike other IA-based schemes in the literature, only local Channel State Information (CSI) is required at nodes. It is shown that for the case of K ≥ M, the total degrees of freedom of 2M − 2 is achievable. The proposed scheme is also extended to the case of K <M based on the ideas of Euclidean distance minimization and time/frequency extension. Finally, simulation results are provided to compare the performance of the proposed scheme with that of the existing results in the literature.