The Impact of Power Allocation on Cooperative Non-orthogonal Multiple Access Networks With SWIPT

In this paper, a cooperative non-orthogonal multiple access (NOMA) network is considered, where a source communicates with two users through an energy harvesting relay. The impact of two types of NOMA power allocation policies, namely NOMA with fixed power allocation (F-NOMA) and cognitive radio inspired NOMA (CR-NOMA), on the considered cooperative simultaneous wireless information and power transfer (SWIPT) system is investigated. In particular, closed-form expressions for the outage probability and their high SNR approximations are derived to characterize the performance of SWIPT-F-NOMA and SWIPT-CR-NOMA. These developed analytical results demonstrate that the two power allocation policies realize different tradeoffs between the reception reliability, user fairness and system complexity. Compared with the conventional SWIPT relaying networks with orthogonal multiple access (OMA), the proposed NOMA schemes can effectively reduce the outage probability, although all of them realize the same diversity gain.

I. Introduction

Non-orthogonal multiple access (NOMA) has recently attracted lots of attention, since it can provide high spectral efficiency and realize massive connectivity in the fifth generation (5G) mobile communication network [1] and [2]. In addition, a two-user special case of downlink NOMA has been adopted by Third Generation Partnership Project (3GPP) Long Term Evolution (LTE), termed multi-user superposition transmission (MUST) [3]. Unlike conventional orthogonal multiple access (OMA), multiple users in a NOMA network are allowed to share the same orthogonal resources in the time, frequency, and code domains. Meanwhile, successive interference cancellation (SIC) is applied at the receiver side, in order to remove the co-channel interference due to the implementation of NOMA [4] and [5].