To appear in IEEE Transactions on Signal Processing, Feb. 2006., revised July 2006.
In this paper, a novel relaying strategy that uses multiple input multiple output (MIMO) fixed relays with linear processing to support multiuser transmission in cellular networks is proposed. This strategy applies to the two hop relaying scenario for coverage enhancement, where the base station transmits data to multiple users through one fixed relay (multiuser transmission). The fixed relay processes the received signal with linear operations and forwards the processed signal to multiple users. This paper proposes upper and lower bounds on the achievable sum rate for this architecture assuming zero forcing dirty paper coding at the base station, neglecting the direct links from the base station to the users, and with certain structure in the relay. These bounds are used to motivate an implementable multiuser precoding strategy that combines Tomlinson-Harashima precoding at the base station and linear signal processing at the relay, adaptive stream selection, and QAM modulation. Reduced complexity algorithms based on the sum rate lower bounds are used to select a subset of users. Simulations compare the upper bounds, lower bounds, and the throughput with Tomlinson-Harashima precoding without coding. These results show that the sum rates achieved by the proposed system architecture and algorithms are close to the sum rate upper bound and the sum rate achieved by the decode-and-forward relaying though decoding at the relay is not required.
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