A Novel Retransmission Scheme for HARQ Enhancement in NOMA Based LTE systems

Long Term Evolution (LTE) standard aims for high data rate transmission in the order of several hundreds of Mbps. Non-Orthogonal Multiple Access (NOMA) transmission is proposed in LTE-Advanced (LTE-A) systems to increase the cell throughput. NOMA based transmission allows the eNodeB (eNB) to multiplex the different users' signals in power domain in a frequency-time grid. In this paper, a novel Hybrid Automatic Repeat and reQuest (HARQ) scheme is proposed for NOMA based transmission. In the proposed method, power level of users are adjusted dynamically in re-transmissions in order to reduce the number of attempts for successful transmission of packets. This will increase the overall cell throughput and reduce power consumption at UE. The proposed method is applied on the Incremental Redundancy (IR) form of HARQ scheme. System level simulations are carried out by considering LTE system parameters. Based on the results, the proposed method improves the cell throughput by reducing the number of retransmissions in HARQ process considerably.