Large Intelligent Surface Assisted MIMO Communications
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This work focuses on the downlink of a single-cell multi-user (MU) system in which a base station (BS) equipped with M antennas communicates with K single-antenna users through a large intelligent surface (LIS) installed in the line-of-sight (LoS) of the BS. LIS is envisioned to offer unprecedented massive multiple-input multiple-output (MIMO) like gains by utilizing N passive reflecting elements that induce phase shifts on the impinging electromagnetic waves to smartly reconfigure the signal propagation. We study the minimum signal-to-interference-plus-noise ratio (SINR) achieved by the optimal linear precoder (OLP), that maximizes the minimum SINR subject to a given power constraint for any given LIS phase matrix, for the cases where the LoS channel matrix between the BS and the LIS is of rank-one and of full-rank. In the former scenario, the minimum SINR is bounded by a quantity that goes to zero with K > 1. For the high-rank scenario, we develop accurate deterministic approximations for the parameters of the asymptotically OLP, which are then utilized to optimize the LIS phase matrix. Simulation results show that the LIS-assisted system can offer Massive MIMO like gains with a much fewer number of active antennas, thereby significantly reducing the energy consumption at the BS.
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