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# Cooperative Non-Orthogonal Multiple Access with SWIPT over Nakagami-$m$ Fading Channels

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To meet with both the energy and spectral efficiency, cooperative non-orthogonal multiple access (NOMA) (termed as CNOMA) and simultaneous wireless information and power transfer (SWIPT) are integrated in this paper. Two different protocols such as CNOMA-SWIPT-PS and CNOMA-SWIPT-TS are proposed, by employing power-splitting (PS) and time-switching (TS) energy harvesting techniques, respectively. In the proposed protocols, a base station directly communicates with a NOMA near user, whereas the communication with a NOMA far user is performed with the assistance of an energy constrained relay node. The relay node harvests energy from the transmitted signal by the base station, employing PS or TS energy harvesting technique. We investigate ergodic sum capacity and outage probability of the proposed protocols along with analytical derivations over Nakagami$-m$ fading channels. Finally, the effectiveness of the proposed schemes over existing strategy and conventional multiple access is demonstrated through analysis and simulation.
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Received: 1 July 2018 Revised: 23 September 2018 Accepted: 20 November 2018
DOI: 10.1002/ett.3571
RESEARCH ARTICLE
Cooperative non-orthogonal multiple access with SWIPT
Md. Fazlul Kader1Mohammed Belal Uddin2Anik Islam2Soo Young Shin2
1Department of Electrical and Electronic
Engineering, University of Chittagong,
2Department of IT Convergence
Engineering, Kumoh National Institute of
Technology, Gumi, South Korea
Correspondence
Electrical and Electronic Engineering,
University of Chittagong,
Funding information
MSIT (Ministry of Science, ICT), Korea,
Grant/Award Number:
IITP-2018-2014-1-00639
Abstract
To meet with both the energy and spectral efficiency, cooperative
non-orthogonal multiple access (NOMA) (termed as CNOMA) and simul-
taneous wireless information and power transfer (SWIPT) are integrated
in this paper. Two different protocols such as CNOMA-SWIPT-PS and
CNOMA-SWIPT-TS are proposed, by employing power-splitting (PS) and
time-switching (TS) energy harvesting (EH) techniques, respectively. In the pro-
posed protocols, a base station (BS) directly communicates with a NOMA near
user, whereas the communication with a NOMA far user is performed with the
assistance of an energy-constrained relay node. The relay node harvests energy
from the transmitted signal by the BS, employing PS or TS EH technique. We
investigate ergodic sum capacity and outage probability of the proposed pro-
tocols along with analytical derivations over Nakagami-mfading channels.
Finally, the effectiveness of the proposed schemes over existing strategy and
conventional multiple access is demonstrated through analysis and simulation.
1INTRODUCTION
To cope with the anticipated challenges of the future wireless networks, fifth-generation wireless systems, abbreviated
5G, are expected to be emerged by 2020.1,2Among the various challenging requirements of 5G, spectral efficiency and
energy efficiency are the two key requirements. To deal with both of these requirements, non-orthogonal multiple access
(NOMA) and simultaneous wireless information and power transfer (SWIPT) can be integrated, which is the main focus
of this paper.
NOMA is an exciting and emerging multiple access technique, which is viewed as one of the key players in 5G, because
of its manifold spectral gains.3-5In a NOMA-based system, multiple signals are superimposed in power domain at the
transmitter side, by the same code at the same frequency, which is unlike the conventional multiple access (orthogonal
multiple access [OMA]) schemes (eg, frequency/time/code division multiple access). At the receiver side, signal decoding
technique such as successive interference cancelation (SIC) can be carried out to decode each signal.6NOMA can be
applied in a wide range of application scenarios. Among them, cooperative NOMA is one of the most active areas of
research. Cooperative NOMA can be broadly categorized into two different types.7In the first type, NOMA-strong users
act as relays to the NOMA-weak users.8On the contrary, dedicated relays are used to assist the NOMA users,9-13 in the
second type. In general, users residing close to the base station (BS) are called strong or near users, whereas users residing
close to the cell edge are called weak or far users.
Because of the vast amount of coexisting wireless technologies, radio frequency (RF) signals are abundant in nature.
These RF signals can be exploited to harvest energy for powering up the energy-constrained nodes.14,15 To prolong the
Trans Emerging Tel Tech. 2019;30:e3571. wileyonlinelibrary.com/journal/ett © 2019 John Wiley & Sons, Ltd. 1of16
https://doi.org/10.1002/ett.3571
... Corollary 2. The AOP of SU 1 as I th → ∞ can be obtained by setting lim (11) and is given by (13) P FD,asy ...
... Instead, P S and P R are directly related to P max , as can be observed in (2). Accordingly, the AOP (as I th → ∞ ) given by (13) is independent of I th . In this case, the OP becomes lower, as P max is increased since it allows both the SBS and the relay to choose larger values for P S and P R . ...
... log(I th ) . Substituting (13) in this equation and simplifying further, the diversity order can be observed to be zero. Furthermore, setting either I th → 0 or P p → ∞ in (12) makes the AOP → 1. ...
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This article considers non‐orthogonal multiple access (NOMA) enabled full‐duplex (FD) underlay cognitive relay networks (ie, NOMA‐FDCRNs) with partial relay selection scheme. The secondary network, where NOMA is used, consists of a secondary base station (SBS) sending messages to two secondary users (SUs), that is, a near SU (SU1) and a far SU (SU2), by utilizing a dedicated relay selected from a set of FD decode‐and‐forward nodes. We obtain analytical expressions for the outage probabilities (OPs) of the SUs and then deduce the asymptotic OP expressions as well. Further, expressions are obtained for the optimal power allocation (OPA) coefficients at the SBS and at the relay that separately maximizes the throughput of the secondary network in NOMA‐FDCRN. Furthermore, the jointly optimal power allocation (JOPA) coefficients that maximize the throughput are also determined. The analyses consider (i) imperfect successive interference cancelation conditions, (ii) the tolerable interference limit of the primary receiver, (iii) the secondary nodes' maximum transmit power values, (iv) interference generated by the primary transmitter, and (v) the residual self‐interference (RSI) at the FD relay. It is shown that the proposed OPA coefficients at the SBS and the JOPA can mitigate the impact of RSI and significantly improve the OP and throughput performance. The numerical results show that the proposed JOPA approach provides 32% and 106% improvement of throughput compared to random power allocation (RPA) and equal power allocation (EPA) strategies, respectively. The OP of SU1 and SU2 reduce by 68% and 73%, respectively, under the proposed JOPA compared to RPA, while compared to EPA, the OP of SU1 and SU2 reduce by 96% and 97%, respectively.
... In Fig. 2 the two phases are represented, where power-switching and energy-harvesting methods, exploiting the whole time slot for both energy and data transmission are considered [42]. This makes the proposed scenario distinct from the cooperative NOMA algorithms previously proposed in the literature, which are based on time switching for the energy harvesting [45][46][47]. Although time switching has convenient hardware implementation, it fully dedicates one time slot for energy transmission which is a disadvantage from the throughput efficiency point of view [48]. ...
... 1 signal is the strongest, i.e., |ℎ 10 | 2 2 ′ + |ℎ 20 | 2 2 < |ℎ 10 | 2 1 : Similar to the previous case, (41) is formulated as (46). Then, for → ∞ and 2 , 1 = 1 , the diversity order of 1 is obtained as follow: ...
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... The performance investigation of NOMA system has recently been the subject of a lot of research work. [11][12][13][14][15][16][17][18][19][20] In Reference 11, effect of user pairing on the downlink NOMA network performance is discussed and compared with that of OMA system. The strategy of pairing and admission with NOMA users is discussed in References 12,13, which significantly enhances the performance of MIMO-NOMA system. ...
... Therefore, to obtain overall optimum performance, the rate requirement of the f th UE needs to be ensured to get the optimum performance. Further, the rate requirements of the f th and the nth UEs are always satisfied at the optimum power allocation and hence O f = O n = 0 and O o f = O o n = 0, which can also be verified by substituting (32) and (34) into (7), (11) and (15), (18) respectively. ▪ ...
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... Integrated performance of NOMA with other techniques such as cooperative communication, simultaneous wireless information and power transfer (SWIPT) and MIMO have been proposed recently. 41,42 Sum rate has been used as a performance metric and also as an objective to formulate various optimization problems in MIMO-NOMA systems. 43,44 A zero-forcing (ZF) receiver-based user pairing and beamforming were studied in downlink multiuser NOMA networks, assuming perfect channel state information (CSI) at the transmitter. ...
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... where, Q * is the amount of energy consumed by the receiver circuit and, R * 1 is the target rate of CEU 1 . Substituting for Q 1 and R 1 , Equation (20) can be rewritten as, ...
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... For example, in [12][13][14], different types of NOMA-SWIPT cooperative relay network models are proposed, and the resource allocation optimization methods is studied with the goal of outage performance of the networks. On this basis, other studies also comprehensively consider the impact of the throughput [15][16][17][18][19], diversity gain [20][21][22], and user transmission distance [23,24], verifying that the cooperative relay network of NOMA-SWIPT fusion has a good prospect in energy and resource optimization. Due to the adoption of the relay cooperation scheme, under the multi-relay model, the reasonable formulation of the relay selection methods can effectively improve the network performance. ...
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Matlab code of the paper: N. T. Do, D. B. da Costa, T. Q. Duong, and B. An, “A BNBF User Selection Scheme for NOMA-Based Cooperative Relaying Systems With SWIPT,” IEEE Communications Letters, vol. 21, no. 3, pp. 664–667, Mar. 2017.
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