Opportunistic MU-MIMO based on semi-blind interference alignment

Recently, Wang etal. [1] proposed MU-MIMO schemes that yield degrees-of-freedom (DoF) gains by enabling blind interference alignment (BIA), i.e., without requiring channel state information at the transmitter (CSIT). This property allows BIA to avoid many CSIT-related resource and system overheads of conventional CSIT-based MU-MIMO. However, BIA requires terminals to have receive antennas that are able to switch between multiple modes. In this paper we present MU-MIMO schemes that exploit a form of semi-blind interference alignment that does not require multiple antenna modes. The schemes are enabled by opportunistic pairing of users based on features of the users´ multipath intensity profiles. This pairing allows suitably remapped versions of the codes in [1] and their extensions to align interference in the frequency domain. The proposed schemes can yield DoF gains with single or multi-antenna terminals, and without requiring antenna-mode switching or transmitter access to fast-changing CSIT. As our representative simulation-based analysis suggests, average DoF gains in the order of 10-25% over SISO (or open loop MIMO) are possible by means of the proposed techniques.