Impartial Cooperation Design in Downlink NOMA Systems with SWIPT

This paper advocates an impartial cooperation scheme in simultaneous wireless information and power transfer (SWIPT)-assisted downlink non-orthogonal multiple access (NOMA) system, consisting of a base station, a far user group and a near user group. Compared to the conventional designs for SWIPT-assisted cooperative NOMA transmissions, the spatial randomness of user locations is taken into account and both the near and far users can act as energy harvesting relays. Under the proposed transmission model, the near and far users can forward information to each other. Owing to the fact that the user locations have tremendous effect on the system performance, the user pairing scheme is devised. With the proposed scheme, closed-form expressions for the outage probability (OP) and diversity order are otained. From theoretical analysis, it is found the proposed impartial SWIPT-assisted cooperative NOMA scheme can reduce the OP and improve the diversity order of the near user, while reaching the same performance of the far user, by comparing to the conventional scheme. Numerical results demonstrate the correctness of the theoretical analysis and present the outage performance superiority of the proposed scheme to existing schemes.