This paper investigates an effective resource utilization scheme for the decode-and-forward (DF) cooperative relaying networks (CRNs) with non-orthogonal multiple access (NOMA). Considering a T time slots transmission, the proposed effective resource utilization scheme adopts max-min relay selections to satisfy the quality-of-service (QoS) and provide a higher priority. Unlike the conventional CRNs, to improve the system performance and resource utilization, the unselected relays will continue receiving the signals transmitted by the base station (BS), as well as the selected relays forward the decoded signals to the user equipment (UE). Moreover, the maximum ratio combining (MRC) is utilized at the UE to jointly detect the receptions for each time slot. The achievable average sum-rate (SR) of the proposed system is analyzed for independent Rayleigh fading channels, and the asymptotic expressions are also provided. The qualitative numerical results corroborating our theoretical analysis show that the proposed effective resource utilization scheme significantly improves the transmission rate and SR performance in comparison to the conventional CRN-NOMA schemes. INDEX TERMS Non-orthogonal multiple access (NOMA), cooperative relaying networks (CRN), ergodic sum-rate (SR), decode-and-forward (DF), quality-of-service (QoS).

This paper focuses on an effective resource utilization scheme for the cooperative relay selection (RS) system with non-orthogonal multiple access (NOMA). In this work, an opportunistic suboptimal RS strategy is proposed that considers both of the users; as well as compared with the balanced and random RS schemes. For the proposed effective resource utilization scheme, the relay nodes are selected by incorporating a max-min selection manner to satisfy the quality of service (QoS) of the users; as well as the unselected relays continue receiving the signals transmitted from the base station (BS) for opportunities. In the meanwhile, the selected relay decodes the received superposed signals by employing the successive interference cancellation (SIC), and then reconstructs them into new NOMA signals, which will be forwarded to the users. Moreover, the closed-form expressions in terms of the sum rate (SR) and outage probability of the proposed transmission scheme are derived for independent Rayleigh fading channels. The provided simulation results show that the cooperative NOMA with the proposed effective RS scheme outperforms the existing works, and can also yield a significant performance gain over the orthogonal multiple access (OMA) scheme.INDEX TERMS Non-orthogonal multiple access (NOMA), cooperative NOMA, relay selection (RS), sum rate (SR), outage probability.

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