Smart Hybrid-ARQ (SHARQ) for cooperative communication via distributed relays in LTE-advanced

The work described in this paper proposes two Smart Hybrid-Automatic Repeat Request (SHARQ) schemes with incremental redundancy, that are developed for a dual-hop network of two relays implementing cooperative communication. In a dual-hop network consisting of multiple relays, one of the most challenging tasks is to determine an appropriate trade-off point between the end-to-end block-error rate (BLER) and an additional delay caused due to HARQ retransmissions in two hops. The retransmissions can either be initiated at the relay nodes or at the source node. HARQ protocol for such a network, should therefore be capable of dynamically deciding the node-of-retransmission. The SHARQ schemes proposed here are designed intelligent in a way that they take into account the presence of two relays and the benefit of using cooperative schemes. Basically the system developed here, intends to provide the combined benefits of diversity gain from cooperative schemes and the throughput improvement from SHARQ in a best possible way. This paper explicitly compares the most basic case of single relay system without HARQ and cooperation with the most advanced scenarios of cooperative communication with SHARQ schemes. It is observed that the latter of the two above scenarios results in throughput improvement of almost 4dB in terms of SNR.