Investigation of Transmission Schemes for Millimeter-Wave Massive MU-MIMO Systems

A massive multiuser multiple-input-multiple-output (MU-MIMO) system working at millimeter-wave frequencies is a new concept that has appeared in recent years. In such systems, the sparsity of the beamspace channel matrix makes the channel rank reduction and limited feedback realizable. Based on these preferable features, this paper introduces two kinds of beamspace transformation and exploits their corresponding beamspace characters. Then, the spatial division multiple access (SDMA) and the interference suppression precoding are investigated separately. Considering the advantages and disadvantages of these two traditional schemes, the authors focus on the design of the limited-feedback-based multiuser transmission schemes for millimeter-wave massive MIMO systems. An enhanced SDMA scheme is first proposed in this paper, which utilizes the beamspace sparsity and overcomes the challenges of channel information acquisition and interference control from a general perspective. Based on these, we analyze the interuser interference condition and further propose a joint transmission scheme, which incorporates a double-precoding-based SDMA and an interference suppression precoding. The performances of the proposed schemes are also evaluated via simulation, which show that high system sum-rate capacity could be achieved with only low computational complexity and a small amount of feedback.