Smart NOMA-HARQ for Short Packet Communications

Abstract

In this paper, we address the smart NOMA-HARQ with a one-allowed re-transmission scheme in a two-user uplink scenario to improve users’ fairness. Each user is allowed to re-transmit once provided that its previous packet was not successfully decoded and the BS performs in a smart way during transmission. In the proposed scheme, NOMA-HARQ offers a chance to decrease the number of re-transmissions, and the system throughput is improved compared to conventional NOMAHARQ. Furthermore, the fairness between users increases due to the remarkable reduction in the required number of retransmissions of the far user. In our model, the users’ power allocation is performed via an optimization problem in that the packet error rate is minimized under power constraints. To analyze the system’s dynamics, a Markov model is first proposed. Then, the power splitting ratios are obtained based on the optimization problem results. The simulation results verify that smart NOMA-HARQ outperforms conventional NOMA-HARQ in terms of the PER, fairness, and throughput under the same rate and total received power at the BS.