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This paper focuses on turbo packet combining for multirelay systems operating over multiple-input-multiple-output (MIMO) broadband channels. We consider a relaying protocol that represents a generalization of the classical point-to-point hybrid automatic repeat request (ARQ). In this protocol, relays play the role of packet retransmitters instead of the source. Packet combining has been widely studied for the point-to-point hybrid ARQ, and it has been shown that the virtual-antenna -concept-based combining strategy exhibits block error rate (BLER) performance that is very close to the matched filter bound. However, the extension of this combining strategy to cooperative communications operating under the framework of broadband MIMO channels is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model in such a way that the cooperation is disguised and the multirelay system becomes equivalent to a point-to-point hybrid ARQ. We investigate the outage probability and outage-based power loss of the considered multirelay system. Then, we extend the turbo packet combiner inspired by the virtual antenna concept to cooperative communications. We focus on implementation issues and propose a hybrid combining strategy. Finally, BLER performances are investigated to demonstrate the gain offered by the studied turbo packet combiner.
Date of Publication: Sept. 2012