Enabling relay selection in non-orthogonal multiple access networks: direct and relaying mode (original) (raw)

Performance limits of wireless powered cooperative NOMA over generalized fading

Transactions on Emerging Telecommunications Technologies, 2021

The non‐orthogonal multiple access (NOMA) technique is a prospective solution to support the massive connectivity of an ever‐increasing number of wirelessly connected devices and address the spectrum scarcity issue. In this article, the outage probability and ergodic capacity of a two‐hop cooperative NOMA network with an energy‐limited relaying node are quantified over a generalizedstatistical model. The relay acts in an amplify‐and‐forward mode and performs energy harvesting (EH) using the time‐switching and power splitting relaying protocols. Moreover, the impact of hardware impairments (HIs) is incorporated into the performance evaluation. The obtained results prove the importance of HIs and allow one to evaluate the outage probability and ergodic capacity over various statistical models and system parameters. Finally, the results suggest that the optimal performance at a specific scenario depends on the combination of multiple factors, such as channel conditions, HI level, trans...

Cooperative Non-Orthogonal Multiple Access with Simultaneous Wireless Information and Power

In this paper, the application of simultaneous wireless information and power transfer (SWIPT) to non-orthogonal multiple access (NOMA) networks in which users are spatially randomly located is investigated. A new cooperative SWIPT NOMA protocol is proposed, in which near NOMA users that are close to the source act as energy harvesting relays to help far NOMA users. Since the locations of users have a significant impact on the performance, three user selection schemes based on the user distances from the base station are proposed. To characterize the performance of the proposed selection schemes, closed-form expressions for the outage probability and system throughput are derived. These analytical results demonstrate that the use of SWIPT will not jeopardize the diversity gain compared to the conventional NOMA. The proposed results confirm that the opportunistic use of node locations for user selection can achieve low outage probability and deliver superior throughput in comparison to the random selection scheme.

Outage probability for a multiuser NOMA-based network using energy harvesting relays

Nonlinear Engineering

This article evaluates the energy-harvesting capabilities of a multiuser non-orthogonal multiple access-based system, where energy harvesting relays utilise the power splitting relaying protocol to harvest energy and amplify-and-forward protocol to forward the signals to the connected users. The expressions for each user’s energy harvesting outage probability are calculated and compared to the same system model without energy harvesting. Simulation results show the effectiveness of the energy-harvesting relay nodes and the improved outage probability of each user.

Outage Performance of Generalized Cooperative NOMA Systems with SWIPT in Nakagami-m Fading

Journal of Communications Software and Systems, 2018

This paper investigates cooperative non-orthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) radio networks. A decode-andforward relay deserves a base station to transmit information to two users. Two access schemes are addressed: direct and relay assisted transmission (DRAT) where a line-of-sight exists between the source and destination, and non-direct and relay assisted transmission (nDRAT) where the only access to the final users is through the relay. New closed-form expressions of outage probability are derived at these schemes. A generalization using Nakagami-m fading channels in considered, in order to present a complete cover of relayed NOMA systems with energy harvesting behavior in small scale fading. We consider the impact of time splitting fraction, power allocation and channel parameters on system maintainability and evaluate its maximum data rate transmission with full autonomy. By comparing the two schemes, cooperative NOMA with energy harvesting (EH) in nDRAT scenario outperforms transmission with direct link in terms of outage probability and transmission data rate. Index Terms-Nakagami-m fading,simultaneous wireless information and power transfer, decode-and-forward, non-orthogonal multiple access, energy harvesting, outage probability.

Reducing the Mutual Outage Probability of Cooperative Non-Orthogonal Multiple Access

IEEE Transactions on Vehicular Technology, 2020

In this letter, a new power allocation scheme is proposed to improve the reliability of cooperative non-orthogonal multiple access (CO-NOMA). The strong user is allocated the maximum power, whereas the weak user is allocated the minimum power. This power allocation alters the decoding sequence along with the signal-to-interference plus noise ratio (SINR), at the users. The weak user benefits from receiving multiple copies of the signal whereas the strong user benefits from the higher power allocation. Numerical simulation results show that the proposed scheme has a lower mutual outage probability (MOP) and offers better reliability as compared to the conventional power allocation scheme for CO-NOMA. An exact closed-form expression of MOP is derived for the two-user CO-NOMA system and it is shown that each user achieves full diversity. The proposed allocation is able to achieve approximately 30% higher transmission rate at 15 dB as compared to conventional CO-NOMA in a practical non-power balanced scenario.

Power-domain non orthogonal multiple access (PD-NOMA) in cooperative networks: an overview

Wireless Networks, 2018

Non-orthogonal multiple access (NOMA) scheme is emerging as a favourable multiple access scheme for future 5G networks. Compared to orthogonal multiple access techniques, NOMA provides spectral efficiency, user fairness, better connectivity, enhanced data rate and reduced latency. Thus, NOMA can be a suitable multiple access technique for 5G networks. On the other hand, in wireless networks, cooperation is a well-recognized proven technique for performance enhancement. Cooperative networks offer multiple desirable advantages, including high performance, reliability and greater coverage area. It is believed that in future 5G systems, many existing wireless technologies will be combined with new technologies. Power domain-NOMA (PD-NOMA) has features that can provide opportunities of improved performance and better spectral utilization for downlink cooperative networks. Recently, research works of incorporating PD-NOMA in cooperative networks have gained attention of researchers around the globe. This article surveys the recent research trends in PD-NOMA based cooperative network by reviewing related recent research on performance analysis of cooperative PD-NOMA systems, resources allocation, and impact of relay selection. Additionally, this review article discusses the performance of cooperative PD-NOMA networks when they are integrated with other 5G technologies including cognitive radio, full duplex radio and wireless energy harvesting. Furthermore, some unaddressed issues are highlighted for future research in this area. Keywords Non-orthogonal multiple access (NOMA) Á Cooperation Á Cooperative relay networks Á Cooperative NOMA

Cooperative Non-Orthogonal Multiple Access for Future Wireless Communications

EAI Endorsed Transactions on Industrial Networks and Intelligent Systems, 2018

There is a huge demand for increased connectivity and reliability of devices in the fifth generation and beyond of wireless communications so as to ensure massive connectivity and high spectral efficiency. Recently, powerdomain non-orthogonal multiple access (NOMA) has received considerable attention as a promising multiple access scheme to improve spectrum efficiency. It allows multiple users to share both time and frequency resources by adjusting the power allocation ratio. However, with ever-increasing mobile users and machines in future wireless environments, NOMA still suffers from some challenges such as a limited connectivity, channel uncertainty and a trade-off between throughput and user fairness. Therefore, an opportunity exists for developing NOMA features in a cooperation of such devices. In this paper, we focuses on exploring cooperative power-domain NOMA systems to maximize potential and develops an effective multiple access for next generation wireless systems. To explore the trade-off of the cooperative NOMA system between its performance and the network complexity, several NOMA systems along with various techniques are introduced. Firstly, a joint NOMA and partial relay selection is introduced to improve both system throughput and user fairness. Secondly, a cooperative NOMA scheme which uses a cognitive radio network as an underlay is also introduced. In this work, a cooperative scheme is used to enhance the outage performance at a cell-edge user for user fairness and NOMA aims to improve spectral efficiency. Finally, an opportunistic NOMA under unreliable wireless backhauls and fronthaul channel uncertainty is introduced and two opportunistic selection rules are applied to a joint NOMA scheme and cooperated transmission. In this work, the impact of unreliable wireless backhauls and fronthaul channel uncertainty on the coordinated NOMA system is examined.

Performance Analysis of Hybrid Relay Selection in Cooperative NOMA Systems

FOREX Publication, 2024

Cooperative NOMA is a method to improve the system performance, this could be done by enabling a user to relay the signal to other users or a dedicated relay. Several dedicated hybrid relays are distributed to forward the source’s signal to the destinations to further enhance the system and serve the users at the cell edge. However, operating several relays simultaneously reduces the spectral efficiency because they need orthogonal channels. Thus, hybrid relay selection is proposed and investigated as a cooperative technique to improve NOMA performance. The relay that provides the highest SNR channel is enabled to relay the signal while the other relays are disabled. BER, outage probability, and channel capacity are measured and investigated to assess the overall system performance. These indicators show that this relay selection is feasible, moreover, relay selection enhances the system reliability, flexibility, and data throughput.

Residual Transceiver Hardware Impairments on Cooperative NOMA Networks

This paper investigates the impact of residual transceiver hardware impairments (RTHIs) on cooperative non-orthogonal multiple access (NOMA) networks, where generic α − µ fading channel is considered. To be practical, imperfect channel state information (CSI) and imperfect successive interference cancellation (SIC) are taken into account. More particularly, two representative NOMA scenarios are proposed, namely non-cooperative NOMA and cooperative NOMA. For the non-cooperative NOMA, the base station (BS) directly performs NOMA with all users. For the cooperative NOMA, the BS communicates with NOMA users with the aid of an amplify-and-forward (AF) relay, and the direct links between BS and users are existent. To characterize the performance of the proposed networks, new closed-form and asymptotic expressions for the outage probability (OP), ergodic capacity (EC) and energy efficiency (EE) are derived, respectively. Specifically, we also design the relay location optimization algorithms from the perspectives of minimize the asymptotic OP. For non-cooperative NOMA, it is proved that the OP at high signal-to-noise ratios (SNRs) is a function of threshold, distortion noises, estimation errors and fading parameters, which results in 0 diversity order. In addition, high SNR slopes and high SNR power offsets achieved by users are studied. It is shown that there are rate ceilings for the EC at high SNRs due to estimation error and distortion noise, which cause 0 high SNR slopes and ∞ high SNR power offsets. For cooperative NOMA, similar results can be obtained, and it also demonstrates that the outage performance of cooperative NOMA scenario exceeds the non-cooperative NOMA scenario in the high SNR regime.

Cooperative NOMA With Incremental Relaying: Performance Analysis and Optimization

IEEE Transactions on Vehicular Technology

In conventional cooperative non-orthogonal multiple access (NOMA) networks, spectral efficiency loss occurs due to a half-duplex constraint. To address this issue, we propose an incremental cooperative NOMA (ICN) protocol for a twouser downlink network. In particular, this protocol allows the source to adaptively switch between a direct NOMA transmission mode and a cooperative NOMA transmission mode according to a 1-bit feedback from the far user. We analytically prove that the proposed ICN protocol outperforms the conventional cooperative NOMA protocol. In addition, an optimal power allocation strategy at the source is studied to minimize the asymptotic system outage probability. Finally, numerical results validate our theoretical analysis, present insights, and quantify the enhancement achieved over the benchmark scheme.