Distributed Turbo Coding Techniques with HARQ at Relays for LTE-A

Advanced relaying concepts that enhance capacity on top of coverage need to be investigated in future releases of LTE-Advanced. In this context, the challenge of our work is to design novel distributed HARQ protocols for cooperative transmissions. The analysis will focus on a relay channel in which source and relay cooperatively construct a distributed turbo code (DTC), but the proposed strategy could be extended to other forward error correction (FEC) schemes. What we propose is to exploit the instantaneous mutual information knowledge at the receiver location. Then in order to select the node that retransmits we check the quality not only of the relay-to-destination channel, but also of the source-to-destination one. Moreover, outage probability is considered to evaluate the link quality between relay and destination and to estimate/predict if retransmission will fail. Simulation results show that the proposed distributed HARQ protocols can significantly enhance the User Equipment (UE) throughput and residual Packet Error Rate (PER).