Separated Horizontal and Vertical Transmission Methods in Massive MIMO Systems

Massive MIMO is a promising technology in 5G communications, it can provide large numbers of antennas and form accurate beams to the users. In conventional three dimensional (3D) MIMO studies, the antenna elements (AEs) in one column are usually virtualized as one antenna port and the transmission schemes in long term evolution system (LTE) or other systems can be reused. In this case, multi-stream transmission can only be supported by the horizontal direction. While in massive MIMO systems with more AEs, forming one antenna port in the vertical direction to support single stream transmission will be inefficient. In this paper, we propose two joint port virtualization and multi-stream transmission algorithms in the framework of separated horizontal and vertical feedback. The proposed algorithms make a better tradeoff between the beamwidth and the number of simultaneously supported data streams. A rank indication (RI) feedback scheme is also proposed to assist the multi-stream transmission.