Harvesting both rate gain and diversity gain: Combination of NOMA with the Alamouti scheme

In this paper, we propose a new method in which the recently proposed non-orthogonal multiple access (NOMA) is combined with the conventional Alamouti scheme. The developed analytical results and simulation both show that if the targeted data rates and the allocated power satisfy an inequality constraint, then our proposed method can effectively increase the diversity order of NOMA from 1 to 2, the same as the Alamouti scheme used in conventional orthogonal multiple access(OMA). Moreover, we define the ∊-achievable rate region as criterion to evaluate the achievable rate gain of the proposed method, and derive closed-form expressions of the ∊-achievable rate region of both the proposed method and OMA-based Alamouti scheme. Simulation shows that the ∊-achievable rate region of OMA-based Alamouti scheme is strictly a sub-region included in that of the proposed method. The conclusion of this paper is that NOMA can be effectively combined with Alamouti scheme to get the benefits of both the rate gain of NOMA and the diversity gain of Alamouti scheme.