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 he 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 low-complexity 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.