Network code assisted HARQ scheme in multi-user systems with cooperative relays

A multi-user network code assisted HARQ system with cooperative relay is proposed. Uplink (UL) transmission with multiple mobile-stations (MSs) cooperating with a relay-station (RS) using HARQ is considered. The RS is assumed to be able to successfully monitor and decode the packets transmitted from the MSs to the base-station (BS). The BS partitions the incorrectly decoded packets into groups based on their MS-to-BS channel conditions and feedback this partition to the RS along with the acknowledgement (ACK) or negative acknowledgement (NACK). The RS employs, for each group inside the partition, a network-coded HARQ scheme using packets in that group for subsequent retransmissions. We proposed a dynamic and adaptive partitioning method based on the channel state information at the BS and the corresponding HARQ retransmission schemes. Also, we derived the corresponding lowcomplexity joint demodulation and decoding structure for this multi-user HARQ scheme. We found via simulations that our proposed scheme can improve the system throughput by around 15% when compared with the simple relay assisted chase combining HARQ system.