Conventional Cooperative Non-orthogonal Multiple Access Research Articles

Cooperative NOMA Based on OAM Transmission for Beyond 5G Applications

Cooperative non-orthogonal multiple access (NOMA) is heavily studied in the literature as a solution for 5G and beyond 5G applications. Cooperative NOMA transmits a superimposed version of all users’ messages simultaneously with the aid of a relay, after that, each user decodes its own message. Accordingly, NOMA is deemed as a spectral efficient technique. Another emerging technique exploits orbital angular momentum (OAM), where OAM is an attractive character of electromagnetic waves. OAM gathered a great deal of attention in recent years (similar to the case with NOMA) due to its ability to enhance electromagnetic spectrum exploitation, hence increasing the achieved transmission throughput. However, OAM-based transmission suffers from wave divergence, especially at high OAM orders. This OAM limitation reduces the transmission distance. The distance can be extended via cooperative relays (part of cooperative NOMA). Relay helps the source to transmit packets to the destination by providing an additional connection to handle the transmission and provide a shorter distance between source and destination. In this paper, we propose employing OAM transmission in the cooperative NOMA network. Simulation experiments show that OAM transmission helps cooperative NOMA in achieving higher throughput compared to the conventional cooperative NOMA. Concurrently, the cooperation part of cooperative NOMA eases the divergence problem of OAM. In addition, the proposed system outperforms the standalone cooperative OAM-based solution.

Cooperative NOMA system with incremental relaying over Nakagami-m fading channels

In our article, we apply incremental relay to the cooperative non-orthogonal multiple access network, in which the incremental relay employs amplify and forward protocol. The main communication process of the system is that one base station transmits messages to multiple non-orthogonal multiple access users with the assistance of incremental relay. In addition, we deeply analyze the outage behavior of the incremental cooperative non-orthogonal multiple access system over Nakagami- m fading channels. Specifically, the exact and asymptotic closed-form expressions of outage probabilities are all derived for paired users u n and u f, which are nearby and distant user, respectively. On this basis, the diversity orders of the paired users u n and u f are also acquired, which are μ ( n+ f+1) and μ( f+1). We also investigate the conventional cooperative non-orthogonal multiple access system, which serves as a benchmark of the incremental cooperative non-orthogonal network. Through the proof, we can conclude that the outage behavior of the distant u f has been improved by adopting incremental relay. Finally, the performance of the system is simulated. The following conclusions can be drawn from the numerical simulation results: (1) the outage performance and throughput of the system have been significantly improved by using the incremental relay protocol; (2) as the multipath fading [Formula: see text] increases, the outage performance of the system becomes better; and (3) the greater the difference in channel gain between paired users, the incremental cooperative non-orthogonal system can achieve better outage performance.

Improving Physical Layer Security of Cooperative NOMA System with Wireless-Powered Full-Duplex Relaying

Non-orthogonal multiple access (NOMA) and wireless energy harvesting are two promising technologies for improving spectral efficiency and energy efficiency, respectively. In this paper, we study the physical layer security of a wireless-powered full-duplex (FD) relay-aided cooperative NOMA system. In particular, the source is wiretapped by an eavesdropper, and the FD relay assists the transmission from the source to a near user and a far user with self-energy recycling. To enhance the security performance of the system, we propose an artificial noise (AN)-aided cooperative transmission scheme, in which the relay emits a jamming signal to confuse the eavesdropper while receiving the signal from the source. For the proposed scheme, the ergodic secrecy sum rate (ESSR) is derived to characterize the secrecy performance and a lower bound of ESSR is obtained. Finally, numerical results verify the accuracy of the theoretical analysis of the proposed AN-aided secure transmission scheme. The superiority of the proposed scheme is also demonstrated since this scheme can achieve better secrecy performance, compared to the conventional cooperative NOMA scheme.

Performance Analysis of Reconfigurable Intelligent Surface‐Aided Full‐Duplex Cooperative NOMA System

The outage performance of a reconfigurable intelligent surface‐ (RIS‐) aided full‐duplex cooperative nonorthogonal multiple access (NOMA) system is studied in this paper. Based on the statistical characteristics of the signal‐to‐noise ratio of the reflection channel from the access point via RIS to the near user, and the cooperative channel from the near user to the far NOMA user, the outage probability of both the near and far users is derived. Through the comparison with the outage performance of conventional cooperative NOMA without employing RIS, the superiority of the proposed scheme is demonstrated. Finally, the correctness of the analytical results is validated with simulation.

Deep Multi-Task Learning for Cooperative NOMA: System Design and Principles

Envisioned as a promising component of the future wireless Internet-of-Things (IoT) networks, the non-orthogonal multiple access (NOMA) technique can support massive connectivity with a significantly increased spectral efficiency. Cooperative NOMA is able to further improve the communication reliability of users under poor channel conditions. However, the conventional system design suffers from several inherent limitations and is not optimized from the bit error rate (BER) perspective. In this article, we develop a novel deep cooperative NOMA scheme, drawing upon the recent advances in deep learning (DL). We develop a novel hybrid-cascaded deep neural network (DNN) architecture such that the entire system can be optimized in a holistic manner. On this basis, we construct multiple loss functions to quantify the BER performance and propose a novel multi-task oriented two-stage training method to solve the end-to-end training problem in a self-supervised manner. The learning mechanism of each DNN module is then analyzed based on information theory, offering insights into the explainable DNN architecture and its corresponding training method. We also adapt the proposed scheme to handle the power allocation (PA) mismatch between training and inference and incorporate it with channel coding to combat signal deterioration. Simulation results verify its advantages over orthogonal multiple access (OMA) and the conventional cooperative NOMA scheme in various scenarios.

Capacity Analysis of an AF Relay Cooperative NOMA System Using MRC

Non-orthogonal multiple access (NOMA) is widely studied in both academia and industry due to its high spectral efficiency over orthogonal multiple access (OMA). To effectively improve spectrum efficiency, an amplify-and-forward (AF) cooperative NOMA system is proposed as well as a novel detection scheme is proposed, in which we first perform successive interference cancellation (SIC) twice at U1 for the two signals received from two time slots to remove interference from symbol 2, then two new signals apply max ratio combining (MRC). In addition, a closed-form upper bound approximation for the ergodic capacity of our proposed system is derived. Monte-Carlo simulations and numerical analysis illustrate that our proposed system has better ergodic capacity performance than the conventional cooperative NOMA system with decode-forward (DF) relay, the conventional cooperative NOMA system with AF relay and the proposed AF cooperative NOMA system in [16]. In addition, we can see that ergodic capacity of all NOMA cooperative systems increase with the increase of transmit SNR. Finally, simulations display that power allocation coefficients have little effect on ergodic capacity of all NOMA cooperative systems. This is due to this fact that ergodic capacity of two symbols can be complementary with changing of power allocation coefficients.

STBC-Aided Cooperative NOMA With Timing Offsets, Imperfect Successive Interference Cancellation, and Imperfect Channel State Information

The combination of non-orthogonal multiple access (NOMA) and cooperative communications can be a suitable solution for fifth generation (5G) and beyond 5G (B5G) wireless systems with massive connectivity, because it can provide higher spectral efficiency, lower energy consumption, and improved fairness compared to the non-cooperative NOMA. However, the receiver complexity in the conventional cooperative NOMA increases with increasing number of users owing to successive interference cancellation (SIC) at each user. Space time block code-aided cooperative NOMA (STBC-CNOMA) offers less numbers of SIC as compared to that of conventional cooperative NOMA. In this paper, we evaluate the performance of STBC-CNOMA under practical challenges such as imperfect SIC, imperfect timing synchronization between distributed cooperating users, and imperfect channel state information (CSI). We derive closed-form expressions of the received signals in the presence of such realistic impairments and then use them to evaluate outage probability. Further, we provide intuitive insights into the impact of each impairment on the outage performance through asymptotic analysis at high transmit signal-to-noise ratio. We also compare the complexity of STBC-CNOMA with existing cooperative NOMA protocols for a given number of users. In addition, through analysis and simulation, we observe that the impact of the imperfect SIC on the outage performance of STBC-CNOMA is more significant compared to the other two imperfections. Therefore, considering the smaller number of SIC in STBC-CNOMA compared to the other cooperative NOMA protocols, STBC-CNOMA is an effective solution to achieve high reliability for the same SIC imperfection condition.

Outage Performance of Downlink Full-Duplex Network-Coded Cooperative NOMA

This letter studies the impact of network-coded multiple access (NCMA) on the outage performance of full-duplex cooperative non-orthogonal multiple access (NOMA). In particular, we propose a network-coded cooperative NOMA (NC-CNOMA) strategy, under which user devices utilize physical-layer network coding (PNC) to demodulate signals with greater probability. The exact analytical expression of the outage probability is derived to evaluate the performance of the proposed scheme. The provided simulation results validate our analysis and the proposed NC-CNOMA scheme outperforms the conventional cooperative NOMA with regard to outage performance.

NOMA-based downlink relaying with media-based modulation

In recent years, non-orthogonal multiple access (NOMA) has attracted considerable attention as a promising multi-access technique for next generation wireless communication systems. Media-based modulation (MBM), which is an emerging index modulation concept, is another technique that can be considered for next generation wireless communication systems due to its high spectral and energy efficiency. In this paper, we propose a NOMA-based decode-and-forward relaying system, where MBM is applied at the source to improve error performance at the relay. We consider a topology consisting of a single source with a single transmit antenna equipped with multiple radio frequency (RF) mirrors, one relay equipped with a single transmit and multiple receive antennas, and multiple users equipped with multiple receive antennas. Pairwise error probability expression for NOMA with multiple receive antennas is derived and the union bound on bit error rate (BER) for the overall system with imperfect successive interference cancellation (SIC) is obtained in closed-form. Analytical results are in agreement with the Monte Carlo simulation results. Moreover, two power allocation optimization problems are formulated in terms of user fairness and quality of service requirements of the users. BER performance of the proposed system is also investigated using the optimum coefficients according to the formulated problems. It is shown that the proposed system outperforms the conventional cooperative NOMA system in terms of error performance as the data rate increases.

Performance Analysis of Cooperative NOMA Systems with Incremental Relaying

In this paper, we investigate the performance of the non-orthogonal multiple access (NOMA) system with incremental relaying, where the relay is employed with amplify-and-forward (AF) or decode-and-forward (DF) protocols. To characterize the outage behaviors of the incremental cooperative NOMA (ICN) system, new closed-form expressions of both exact and asymptotic outage probability for two users are derived. In addition, the performance of the conventional cooperative NOMA (CCN) system is analyzed as a benchmark for the the purpose of comparison. We confirm that the outage performance of the distant user is enhanced when ICN system is employed. Numerical results are presented to demonstrate that (1) the near user of the ICN system achieves better outage behavior than that of the CCN system in the low signal-to-noise ratio (SNR) region; (2) the outage performance of distant user for the DF-based ICN system is superior to that of the AF-based ICN system when the system works in cooperative NOMA transmission mode; and (3) in the low SNR, the throughput of the ICN system is higher than that of the CCN system.

Outage Performance Analysis for SWIPT-Based Incremental Cooperative NOMA Networks With Non-Linear Harvester

This work studies a simultaneous wireless information and power transfer based downlink non-orthogonal multiple access (NOMA) network. The near user is equipped with a non-linear energy harvester, whose non-linear property is depicted by a piecewise linear model. An incremental cooperative NOMA (ICN) protocol is proposed to improve the performance of the considered network. Specifically, based on no more than 2-bit feedback from the far and near users, respectively, the network determines to work in the direct NOMA transmission (DNT), conventional point-to-point communications, or conventional cooperative NOMA (CCN) modes. The outage probabilities and throughput for both the far and near users are derived. Numerical results compare the differences among the proposed ICN, CCN, DNT and orthogonal multiple access protocols in terms of outage performance and system throughput, and exhibit the superior performance of the proposed ICN protocol.

Virtual Full-Duplex Cooperative NOMA: Relay Selection and Interference Cancellation

In this paper, we propose a virtual full-duplex cooperative non-orthogonal multiple access (NOMA) framework for a downlink two-hop network assisted by multiple half-duplex decode–and–forward (DF) relay stations (RSs). In the proposed virtual full-duplex framework, the RSs except for a selected RS to forward the received signal suffer from inter-RS interference since both the BS and the selected RS transmit the super-imposed signal simultaneously. To address this problem, we propose an RS selection algorithm with adaptive inter-RS interference management and we mathematically attain the closed-form outage probability, which is challenging in general. In addition, we investigate diversity-multiplexing tradeoff (DMT) performance of a modified version of the proposed RS selection algorithm based on a discrete Markov chain, which adaptively resets the successive transmission. Simulation results show that the proposed RS selection algorithm outperforms the conventional cooperative NOMA algorithm in terms of both the outage probability and the DMT, which has the best performance reported in the literature.

Non-Orthogonal Multiple Access Assisted Device-to-Device Communication: Best Helping Base Station Approach

<span>It can be studied in this paper that a cooperative non-orthogonal multiple access (NOMA) helps device-to-device (D2D) communication system through base station (BS). In particular, we investigate BS selection scheme as a best channel condition for dedicated devices where a different data transmission demand on each device is resolved. The analysis on amplifying-and forward (AF) relay is proposed to evaluate system performance of the conventional cooperative NOMA scheme. Under the realistic assumption of perfect channel estimation, the achievable outage probability of both devices is investigated, and several impacts on system performance are presented. The mathematical formula in closed form related to probability has also been found. By implementing Monte-Carlo simulation, the simulation results confirm the accuracy of the derived analytical results. Also, the proposed D2D cooperative NOMA system introduces expected performance on reasonable selected parameters in the moderate signal to noise ratio (SNR) regime.</span>

Time Shared Half/Full-Duplex Cooperative NOMA With Clustered Cell Edge Users

This letter proposes time sharing (TS)-based half/full-duplex (HD/FD) cooperative non-orthogonal multiple access (CRNOMA) schemes, namely, TS-HD-CRNOMA and TS-FD-CRNOMA to efficiently utilize the spectrum of unpaired users. A scenario with more cell edge users (CEUs) than cell center users is considered. Both schemes pair a CCU with multiple clustered CEUs in a TS fashion via a relay, thereby efficiently utilizing the frequency bands of multiple CEUs, which may remain underused in conventional CRNOMA. Ergodic sum capacity of the schemes is analytically derived, validated through simulations, and compared with conventional multiple access schemes to show the achieved capacity gains.

Cooperative NOMA With Incremental Relaying: Performance Analysis and Optimization

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 two-user 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.