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Two-level HARQ for turbo coded cooperation: System retransmission gain and optimal time allocation

Hybrid automatic repeat request (HARQ) is a well-known technique for improving system throughput and link performance of wireless communication systems, including cooperative communication systems. In this paper, we exploit the limited feedback applied to the two-source turbo coded cooperation scheme to define a particular cooperative HARQ protocol, called two-level HARQ, where the decision on retransmission at each node is conditioned by two levels: first by the feedback from the destination and second by the feedback from the partner node. To evaluate the performance improvement of this cooperative HARQ system over the original turbo coded cooperation system in terms of frame error probability, we define the system retransmission gain. This gain serves as a decision parameter to determine the conditions under which the cooperative HARQ protocol is useful. Finally, optimal time resource allocation is explored, offering sizable performance improvements.