Optimal selection of cooperative RAUs in HSR based distributed antenna systems and mobile relay with massive antennas

This paper studies the performance and designs of high speed railway (HSR) communications that employ massive multiple-input multiple-output (MIMO) systems, where a mobile relay (MR) with a large number of antennas is mounted on the train. The users onboard the train communicate with the ground base station (BS) via MR, i.e. two-hop communications. The distributed antenna system (DAS) is used on ground, where a BS consists of a central unit (CU) and a number of remote antenna units (RAUs) connecting to the CU by optical fiber. The issue of selecting an optimal cooperative RAU set of a linear DAS for railway scenario is addressed. We present a low complexity approach to select a transmit RAU set for capacity maximization, based on the theory of convex optimization. We show via extensive Monte-Carlo simulations that the proposed algorithm provides performance very close to that of optimal selection based on exhaustive search.