Joint Beamforming and Power-Splitting Control in Downlink Cooperative SWIPT NOMA Systems

Abstract

This paper investigates the application of simultaneous wireless information and power transfer (SWIPT) to cooperative non-orthogonal multiple access (NOMA). A new cooperative multiple-input single-output (MISO) SWIPT NOMA protocol is proposed, where a user with a strong channel condition acts as an energy-harvesting (EH) relay to help a user with a poor channel condition. The power splitting (PS) scheme is adopted at the EH relay. By jointly optimizing the PS ratio and the beamforming vectors, the design objective is to maximize the data rate of the "strong user" while satisfying the QoS requirement of the "weak user". It boils down to a challenging nonconvex problem. To resolve this issue, the semidefinite relaxation (SDR) technique is applied to relax the quadratic terms related with the beamformers, and then it is solved to its global optimality by two-dimensional exhaustive search. We prove the rank-one optimality, i.e., the SDR tightness, which establishes the equivalence between the relaxed problem and the original one. To further reduce the high complexity due to the exhaustive search, an iterative algorithm based on successive convex approximation (SCA) is proposed, which can at least attain its stationary point efficiently. In view of the potential application scenarios, e.g., Internet of Things (IoT), the single-input single-output (SISO) case of the cooperative SWIPT NOMA system is also studied. The formulated problem is proved to be strictly unimodal with respect to the PS ratio. Hence, a golden section search (GSS) based algorithm with closed-form solution at each step is proposed to find the unique global optimal solution. It is worth pointing out that the SCA method can also converge to the optimal solution in SISO cases. In the numerical simulation, the proposed algorithm is numerically shown to converge within a few iterations, and the SWIPT-aided Manuscript

A Survey of Non-Orthogonal Multiple Access for 5G

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“…Moreover, Liu et al [16] proposed a novel protocol for the NOMA aided cooperative network, in which the users close to the transmitters operate as the wireless powered relays for the sake of forwarding the information arXiv:2002.08704v1 [eess.SP] 20 Feb 2020 to the distant users. Xu et al [17] proposed a joint design of the transmit beamforming and receive power splitting in a similar NOMA aided cooperative network, which aims for maximising the achievable throughput of the so-called 'strong users', while ensuring the minimum throughput requirements of other 'weak users'. Diamantoulakis et al [18] studied a wireless-powered communication network, in which the uplink transmission of multi-user is supported by the NOMA.…”

Energy Efficiency of RSMA and NOMA in Cellular-Connected mmWave UAV Networks

“…which implicitly assumes that messages of all the UAVs with the indices greater than m have been decoded successfully and canceled beforehand. Actually, (17) represents the SINR of the kth UAV while decoding its own message (i.e., for m = k), as well. Note that the summation in the denominator of (17) disappears when the kth UAV with k = 1 is decoding its own message (i.e., no possible l index satisfying l < k for this specific case), and we have G k N0 |h H k w k | 2 .…”