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An Optimal User Selection Scheme for Cooperative NOMA Networks with SWIPT
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In this paper, we propose an optimal user selection scheme for cooperative non-orthogonal multiple access (NOMA) networks with simultaneous wireless information and power transfer (SWIPT). By considering decode and forward (DF) protocol, SWIPT is employed at near users to relay information to far users via applying a user selection scheme that selects an optimal pair of near and far users and ensures the correct information decoding at the near user within an adaptive power allocation coefficient (PAC) range. Closed-form expressions for the outage probability of the selected near and far users are derived. We show that the selected near and far users can achieve a diversity gain of N and N + F, respectively, with a significant coding gain, where N and F are the number of near and far users. Simulation results investigate that the proposed scheme can achieve an optimal outage performance over the state of arts.
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... The EE under the C-NOMA outperforms the direct NOMA method due to the lesser transmission power needed at the BS to satisfy the data rate of the FUE. Unlike the aforementioned studies where a single FUE is considered, the authors of [74] consider the scenario where multiple FUE exists. In the study, the expression for an optimal nearest near user and nearest far user (NNNF) pairing is derived in a closed-form. ...
... This is because the diversity order mainly relies on the source-relay and relay-destination links [93]. Consequently, it can be inferred that the achievable diversity gain under SWIPTaided networks is the same as the conventional NOMA networks without SWIPT [74,97]. ...
The concept of integrating cooperative communication in non-orthogonal multiple access (NOMA) based networks (also known as cooperative NOMA) is inspired by the need to enhance network scalability with guaranteed fair resource allocation. However, sustaining the cooperative NOMA (C-NOMA) network lifetime becomes a challenging problem due to the energy bottleneck of the devices acting as relays for weak users. To alleviate this problem, the integration of radio frequency-based energy harvesting technique known as simultaneous wireless information and power transfer (SWIPT) in C-NOMA networks has been proposed. In this article, we present an extensive review of various contributions to the performance analysis of SWIPT-aided C-NOMA networks. To begin with, we identify critical guidelines needed for efficient network design. Moreover, we present an illustration of the system model in order to understand the fundamental relationship among different network components from a technical perspective. Further to this, we categorize and present an in-depth review of notable studies based on the type of relay employed, the number of relays deployed and the type of communication protocol adopted. Finally, we identify open areas worth exploring for future research works.
Non-orthogonal multiple access (NOMA) has been widely recognized as a promising way to scale up the number of users, enhance the spectral efficiency, and improve the user-fairness in wireless networks, by allowing more than one user to share one wireless resource. NOMA can be flexibly combined with many existing wireless technologies and emerging ones including multiple-input multiple-output (MIMO), massive MIMO, millimeter wave communications, cognitive and cooperative communications, visible light communications, physical layer security, energy harvesting, wireless caching, and so on. Combination of NOMA with these technologies can further increase scalability, spectral efficiency, energy efficiency, and greenness of future communication networks. This paper provides a comprehensive survey of the interplay between NOMA and the above technologies. The emphasis is on how the above techniques can benefit from NOMA and vice versa. Moreover, challenges and future research directions are identified.
This paper investigates an effective resource utilization scheme for the decode-and-forward (DF) relaying networks (CRNs) with non-orthogonal multiple access (NOMA). Considering a T time slots transmission, the proposed effective resource utilization scheme adopts max-min relay selections to satisfy the quality-of-service (QoS) and provide a higher priority. Unlike the conventional CRNs, to improve the system performance and resource utilization, the unselected relays will continue receiving the signals transmitted by the base station (BS), as well as the selected relays forward the decoded signals to the user equipment (UE). Moreover, the maximum ratio combining (MRC) is utilized at the UE to jointly detect the receptions for each time slot. The achievable average sum-rate (SR) of the proposed system is analyzed for independent Rayleigh fading channels, and the asymptotic expressions are also provided. Qualitative numerical results corroborating our theoretical analysis show that the proposed effective resource utilization scheme significantly improves the transmission rate and SR performance in comparison to the conventional CRN-NOMA schemes.
In this paper, the problem of communication security in an underlay wiretap cognitive radio network is addressed and statistically investigated. We rely on a simple dual-hop communication model of decode and forward relay assisted network. Regarding the interference from primary users, interference power and maximum transmit power constraints; this network is subjected to multiple eavesdropping attacks which employ a specific interception strategy. To confound this eavesdropping, proposed selection schemes are exploited that aim at maximizing the minimum of the dual secrecy rates in order to strengthen the physical layer security. Moreover, exact and asymptotic closed form expressions are derived for specific performance metrics over independent and identically distributed Rayleigh fading channels. At high signal to interference noise ratio (SINR), tangential system bounds are also derived and discussed. Monte Carlo simulation results emphasize our assumption. It is found out that at the full diversity of the system, any additional node that enters the cooperative eavesdropping system becomes significantly of no effect.
In this letter, we investigate the outage performance of cooperative relaying transmissions in two-user non-orthogonal multiple access (NOMA) systems, wherein simultaneous wireless information and power transfer (SWIPT) is employed at the near users to power their relaying operations. To this end, a best-near best-far (BNBF) user selection scheme is proposed. Considering three relaying protocols, i.e., decode-and-forward (DF), amplify-and-forward (AF), and hybrid DF/AF protocols, tight closed-form approximate expressions for the outage probability (OP) are derived to evaluate the system performance. Numerical results reveal that, for any relaying protocols used, the diversity order achieved by the BNBF scheme is M + 1, where M is the number of far users, and does not depend on the number of near users. Index Terms—Non-orthogonal multiple access (NOMA); out-age performance; simultaneous wireless information and power transfer (SWIPT); user selection.
As the latest member of the multiple access family, non-orthogonal multiple
access (NOMA) has been recently proposed for 3GPP Long Term Evolution (LTE) and
envisioned to be an essential component of 5th generation (5G) mobile networks.
The key feature of NOMA is to serve multiple users at the same
time/frequency/code, but with different power levels, which yields a
significant spectral efficiency gain over conventional orthogonal MA. This
article provides a systematic treatment of this newly emerging technology, from
its combination with multiple-input multiple-output (MIMO) technologies, to
cooperative NOMA, as well as the interplay between NOMA and cognitive radio.
This article also reviews the state of the art in the standardization
activities concerning the implementation of NOMA in LTE and 5G networks.
or downlink signalling, we propose a simple scheme to select one each of N near-users (NUs) and F far-users (FUs), and switch between orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA) signalling so as to improve performance of the FUs significantly, while ensuring that performance of NUs does not degrade below that achieved by OMA alone. We derive a closed-form expression for outage probability of the FU. Assuming that the selected near-user employs successive interference cancellation (SIC) and relays the FU symbols when NOMA is employed, we show that FUs achieve a diversity of N+F when optimal combining is performed, while NUs achieve a diversity of N.
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. Particularly, 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 to 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.
This paper presents a full-duplex device-to-device (D2D)-aided cooperative nonorthogonal multiple access (NOMA) scheme to improve the outage performance of the NOMA-weak user in a NOMA user pair, where the NOMA-weak user is helped by the NOMA-strong user with the capability of full-duplex D2D communications. The expressions for the outage probability are derived to characterize the performance of the proposed scheme. The results show that the proposed cooperative NOMA scheme can achieve superior outage performance compared to the conventional NOMA and orthogonal multiple access (OMA). In order to further improve the outage performance, an adaptive multiple access (AMA) scheme is also studied, which dynamically switches between the proposed cooperative NOMA, conventional NOMA, and OMA schemes, according to the level of residual self-interference and the quality of links. The results show that the AMA scheme outperforms the above multiple access schemes in terms of outage performance.