Adaptive Relaying Protocol Design and Analysis for Short-Packet Cooperative NOMA

This paper designs and characterizes an adaptive relaying protocol in a short-packet cooperative non-orthogonal multiple access (NOMA) network. Particularly, a base station broadcasts a superposed signal to a strong user and a weak user with the help of a dedicated relay. Compared with the conventional fixed decode-and-forward relaying protocol (DFRP) and amplified-and-forward relaying protocol (AFRP), we propose a novel adaptive hybrid relaying protocol (AHRP) for a short-packet cooperative NOMA network, in which the dedicated relay chooses the transmission modes adaptively to help the information transmission of the weak user according to the comparison between the achievable data rates and the target data rates. Moveover, the ergodic rates of the two users are approximated with closed-form expressions and an asymptotic performance comparison among the DFRP, AFRP, and AHRP is also provided. Simulation results indicate that the proposed AHRP outperforms the DFRP and AFRP in terms of users' ergodic rates. Furthermore, the AHRP can achieve higher user rate and robustness than the DFRP, AFRP, and cooperative orthogonal multiple access under various network settings.