Improvement of HARQ based on redundant data of near user in non-orthogonal multiple access

Non-orthogonal multiple access (NOMA) has been viewed as a promising technology in future cellular network to increase channel capacity and frequency efficiency. This NOMA system utilizes power domain to improve the performance of multiple access. Signal detection of a near user is operated by successive interference cancellation (SIC). With SIC, the near user cancels out the signal of far user and decodes its own data. Thereafter, the near user drops the cancelled data if SIC is successful. On the other hand, the far user still needs that the far user data may be retransmitted in case of far user reception failure, i.e., no-acknowledgement. Therefore, retransmission to the far user via the near user is efficient when the near user reuses its cancelled data. In this paper, we investigate more efficient way to conduct hybrid automatic repeat request (HARQ) in NOMA. If the SIC procedure of near user is successful, there is an effective approach to recycle the interference-cancelled data. This concept contains full duplex MIMO technique on near user to support the far user. It is found that the proposed retransmission method provides improvements in view of outage probability, symbol error rate (SER), and throughput of far user.