Cooperative Downlink Research Articles

UAV-Assisted Cooperative Downlink NOMA: Deployment and Resource Allocation

UAV-Assisted Cooperative Downlink NOMA: Deployment and Resource Allocation

Performance Analysis of Downlink Cooperative User Relaying FD/HD NOMA Over Nakagami-$m$ Fading Channels

Performance Analysis of Downlink Cooperative User Relaying FD/HD NOMA Over Nakagami-$m$ Fading Channels

Best sum-throughput evaluation of cooperative downlink transmission nonorthogonal multiple access system

In cooperative simultaneous wireless information and power transfer (SWIPT) nonorthogonal multiple access (NOMA) downlink situations, the current research investigates the total throughput of users in center and edge of cell. We focus on creating ways to solve these problems because the fair transmission rate of users located in cell edge and outage performance are significant hurdles at NOMA schemes. To enhance the functionality of cell-edge users, we examine a two-user NOMA scheme whereby the cell-center user functions as a SWIPT relay using power splitting (PS) with a multiple-input single-output. We calculated the probability of an outage for both center and edge cell users, using closed-form approximation formulas and evaluate the system efficacy. The usability of cell edge users is maximized by downlink transmission NOMA (CDT-NOMA) employing a SWIPT relay that employs PS. The suggested approach calculates the ideal value of the PS coefficient to optimize the sum throughput. Compared to the noncooperative and single-input single-output NOMA systems, the best SWIPT-NOMA system provides the cell-edge user with a significant throughput gain. Applying SWIPT-based relaying transmission has no impact on the framework’s overall throughput.

Power Allocation and Decoding Order Selection for Secrecy Fairness in Downlink Cooperative NOMA With Untrusted Receivers Under Imperfect SIC

Power Allocation and Decoding Order Selection for Secrecy Fairness in Downlink Cooperative NOMA With Untrusted Receivers Under Imperfect SIC

Performance of Novel Adaptive Schemes for Cognitive Full-Duplex Relaying-Based Downlink Cooperative NOMA

In this paper, we demonstrate that due to large variations in link signal-to-noise-ratios, the key to good performance in underlay cooperative non-orthogonal multiple access (CNOMA) is intelligent adaptation. First adaptation involves switching between the cooperative mode (CM) and the non-cooperative mode (NCM). While a full-duplex near user (NU) assists the multiple-antenna base-station in communication to a far user (FU) in CM, allowing the NU to switch to NCM ensures that its performance is same as in a network without the FU. The second adaptation relates to transmit antenna selection. In the first scheme, the NOMA power allocation parameter (NPAP), and the interference temperature limit (ITL) apportioning parameter (ITLAP) depend on channel statistics. The third adaptation (presented for the first time in literature) used in two other proposed schemes involves selection of inter-dependent NPAP and ITLAP based on channel state information (CSI). The fourth adaptation used in the third proposed scheme relates to use of CSI-dependent ITL, which is shown to dramatically improve performance. Optimum choices of NPAP and ITLAP are expressed in closed-form for all three schemes, and performance with these is analyzed (and validated by computer simulations) assuming imperfect successive interference cancellation and residual self-interference cancellation at the NU.

Joint Beamforming and Power Optimization for Cooperative Downlink MIMO Systems

Herein, we propose a joint optimization algorithm to minimize the overall transmit power in multicell multiuser multiple-input multiple-output (MIMO) systems for B5G. The proposed algorithm is an iterative optimization algorithm that jointly computes the transmit/receive beamforming vectors and the transmit power. The superiority of the proposed method is demonstrated through simulations.

Exploiting Cooperative Downlink NOMA in D2D Communications.

We propose and investigate a bidirectional device-to-device (D2D) transmission scheme that exploits cooperative downlink non-orthogonal multiple access (NOMA) (termed as BCD-NOMA). In BCD-NOMA, two source nodes communicate with their corresponding destination nodes via a relaying node while exchanging bidirectional D2D messages simultaneously. BCD-NOMA is designed for improved outage probability (OP) performance, high ergodic capacity (EC) and high energy efficiency by allowing two sources to share the same relaying node for data transmission to their corresponding destination nodes while also facilitating bidirectional D2D communications exploiting downlink NOMA. Simulation and analytical expressions of the OP, EC and ergodic sum capacity (ESC) under both perfect and imperfect successive interference cancellation (SIC) are used to demonstrate the effectiveness of BCD-NOMA compared to conventional schemes.

System throughput maximization in IRS-assisted phase cooperative NOMA networks

This work investigates performance of system throughput in intelligent reflecting surfaces (IRSs)-enabled phase cooperative non-orthogonal multiple access (NOMA) framework. By exploiting heterogeneous cognitive radio networks concept the aim is to maximize the sum rate of secondary users in the proposed phase cooperative downlink network configuration via optimization solutions. However, the optimization problem comes out to be NP-hard and precludes direct solution. Hence, an alternating optimization is applied at the primary network to solve the maximization problem by exploiting the transmit beamforming (BF) at the power station (PS) and phase shift optimization at the IRS. Later, sum rate maximization for secondary network is performed by utilizing phase shifts of primary network via phase cooperation. In order to find global optimal solutions for active beamformers at both PSs, a branch-reduce-and-bound (BRnB) method is used whereas, passive phase shift optimization at the primary PS is performed via a simple iterative solution, i.e., the element-wise block coordinate descent method. For the proposed framework, Monte-Carlo simulations are performed where the optimality of the global solution is compared with heuristic BF methods including minimum-mean-square-error/regularized zero-forcing-beamforming (ZFBF) and ZFBF. The BRnB algorithm sets an upper performance bound by improving the sum rate of users in comparison with the conventional heuristic BF schemes. This work signifies the utilization of phase cooperation in IRS-assisted NOMA networks for a multi-user environment.

Performance analysis of 5G Downlink Cooperative NOMA network with multi-antenna relay

In this paper, a 5G Downlink Cooperative amplify-and-forward (AF) NOMA communication system with multi-antenna relay is investigated. By exploring the advantage of multiple antenna, the best antenna selecting and switching scheme at relay is considered. Then the analytical expressions for outage probability and ergodic sum rate are derived, and the asymptotic result for outage probability is also obtained to give easy evaluation. Based on the results, the effects of the important system parameters, such as antenna number, the outdated channel side information(CSI), power allocation, are analyzed. From the asymptotic formula, we find that the system can get the diversity order N, which is the antenna number at the relay, when perfect CSI can be obtained. And the diversity order decreases to one when outdated CSI appears, regardless of multi-antenna. Computer simulations are also done to validate the correctness of theoretical analysis.

Sum-Rate Maximization of Multicell MISO Networks With Limited Information Exchange

Although there have been extensive studies on transmit beamforming in multi-input single-output (MISO) multicell networks, achieving optimal sum-rate with limited channel state information (CSI) is still a challenge even with a single user per cell. A novel cooperative downlink multicell MISO beamforming scheme is proposed with highly limited information exchange among the base stations (BSs) to maximize the sum-rate. In the proposed scheme, each BS can design its beamforming vector with only local CSI based on limited information exchange on CSI. Unlike previous studies, the proposed beamforming design is non-iterative and does not require any vector or matrix feedback but requires only quantized scalar information. The proposed scheme closely achieves the optimal sum-rate bound in almost all signal-to-noise ratio regime based on non-iterative optimization with lower amount of information exchange than existing schemes, which is justified by numerical simulations.

Relay Selection-aware Non-orthogonal Multiple Access Networks: Direct and Relaying Mode

Objective: In this paper, Decode-and-Forward (DF) mode is deployed in the Relay Selection (RS) scheme to provide better performance in cooperative downlink Non-orthogonal Multiple Access (NOMA) networks. In particular, evaluation regarding the impact of the number of multiple relays on outage performance is presented. Methods: As main parameter affecting cooperative NOMA performance, we consider the scenario of the fixed power allocations and the varying number of relays. In addition, the expressions of outage probabilities are the main metric to examine separated NOMA users. By matching related results between simulation and analytical methods, the exactness of derived formula can be verified. Results: The intuitive main results show that in such cooperative NOMA networks, the higher the number of relays equipped, the better the system performance can be achieved. Conclusion: DF mode is confirmed as a reasonable selection scheme to improve the transmission quality in NOMA. In future work, we will introduce new relay selections to achieve improved performance.

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

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

Finite Blocklength Non-Orthogonal Cooperative Communication Relying on SWIPT-Enabled Energy Harvesting Relays

A finite blocklength (FBL) twin-user non-orthogonal cooperative downlink system is considered, wherein a base station simultaneously communicates with the users whilst relying on simultaneous wireless information and power transfer (SWIPT) enabled energy harvesting relay. Closed-form analytical expressions are obtained for the end-to-end average block error rate (BLER) assuming potentially dissimilar Nakagami- $m$ fading links. Furthermore, asymptotic expressions are derived for the individual user’s end-to-end average BLER performance and diversity order at high signal to noise ratios (SNRs). Additionally, since, the stronger user’s signal is detected, while assuming the weaker user’s signal to be interference, an analytical bound has been obtained for characterizing the effect of this interference on the BLER performance of both users. Furthermore, a framework is developed for joint relay splitting factor and user power allocation towards end-to-end blocklength minimization under strict reliability constraints by converting the original non-convex optimization problem to a convex geometric program (GP) that can be solved efficiently. Simulation results are presented to validate the analytical expressions derived and illustrate the efficacy of the proposed scheme.

Secrecy-Enhancing Design for Cooperative Downlink and Uplink NOMA With an Untrusted Relay

We investigate a secrecy-enhancing design for cooperative downlink and uplink non-orthogonal multiple access (NOMA) transmissions with an untrusted relay. A source uses the NOMA principle to have downlink and uplink transmissions with a near user and a far user, and the communications between the source and the far user are aided by an untrusted relay. To minimize information leakage at the untrusted relay and achieve secure NOMA communications, adaptive downlink and uplink cooperative jamming schemes are proposed, where the far user in downlink and the near user in uplink adaptively emit a jamming signal to the untrusted relay to impair its eavesdropping capability. Both downlink and uplink jamming power are optimized to fully exploit the benefits of the proposed schemes for security enhancement. Then, for each scheme, we quantify the secrecy performance by deriving the ergodic secrecy sum rate lower bound and its scaling law. Finally, computer simulation is used to demonstrate the effectiveness of the proposed adaptive downlink and uplink cooperative jamming schemes and verify the accuracy of the derived analytical results.

UAV-assisted cooperative downlink NOMA with virtual full-duplex operation

UAV-assisted cooperative downlink NOMA with virtual full-duplex operation

Cooperative Downlink Interference Transmission and Cancellation for Cellular-Connected UAV: A Divide-and-Conquer Approach

The line-of-sight dominant air-ground channels have posed critical interference issues in cellular-connected unmanned aerial vehicle (UAV) communications. In this paper, we propose a new base station (BS) cooperative beamforming (CB) technique for the cellular downlink to mitigate the strong interference caused by the co-channel terrestrial transmissions to the UAV. Besides the conventional CB by cooperatively transmitting the UAV's message, the serving BSs of the UAVs exploit a novel interference transmission scheme to effectively suppress the terrestrial interference to the UAV. Specifically, the co-channel terrestrial users' messages are shared with the UAV's serving BSs and transmitted via CB to cancel their resultant interference at the UAV. To balance between the CB gains for UAV signal enhancement and interference cancellation, we aim to maximize the UAV's receive signal-to-interference-plus-noise ratio by jointly optimizing the power allocations at all of its serving BSs for transmitting the UAV's and co-channel terrestrial users' messages. First, we derive the closed-form optimal solution to this problem in a special case and draw useful insights. Then, we propose an algorithm to solve the problem optimally in the general case. As the optimal solution requires centralized implementation with exorbitant message/channel information exchanges among the BSs, we further propose a distributed algorithm that is amenable to practical implementation, based on a new divide-and-conquer approach, whereby each co-channel BS divides its perceived interference to the UAV into multiple portions, each to be canceled by a different serving BS of the UAV with its best effort. Numerical results show that the proposed centralized and distributed CB schemes with interference transmission and cancellation (ITC) can both significantly outperform the conventional CB without applying ITC.

Secrecy Outage Performance Analysis for Cooperative NOMA Over Nakagami-$m$ Channel

In this paper, we investigate the secrecy outage performance of a typical cooperative downlink non-orthogonal multiple access (NOMA) system over Nakagami-m fading channel, in which the base station transmits a superimposed signal to two users via a relay. First, the secrecy outage behavior of the considered system over Nakagami-$m$ fading channel under three wiretapping cases, e.g., one eavesdropper (Eve), non-colluding and colluding eavesdroppers, are studied, and both analytical and asymptotic expressions for the secrecy outage probability are derived. Next, by considering the availability of Eves' channel state information, we adopt the two-stage relay selection (RS) strategy to improve the system's secrecy outage performance. Finally, simulation results are provided to corroborate the accuracy of our derived expressions. The results show that: 1) there exists secrecy performance floor for cooperative NOMA system, and it was determined by the weak user's secrecy requirement and the channel conditions of the Eves; 2) the two-stage RS scheme can increase the secrecy outage performance significantly under three wiretapping cases; 3) the secrecy performance of cooperative NOMA network is superior to that of orthogonal multiple access network on the condition of low and medium signal-to-noise ratio regions.

Cooperative Network Operation Design for Mobility-Aware Cloud Radio Access Network

Ultra-dense small cells operating in a cooperative manner, such as cloud radio access network (C-RAN), have been introduced to serve the numerous mobile devices in the next generation wireless networks. One of the major challenges in efficiently operating the C-RAN in a cooperative manner is the excessive overhead signaling and computation load, such as downlink channel state information (CSI) acquisition at the cloud for cooperative downlink transmission, which scales rapidly with the size of the network. In this paper, the exploitation of mobility information of devices is proposed to address the challenge of efficiently operating the C-RAN. We introduce a mobility-assisted CSI acquisition method to complement conventional pilot-based CSI acquisition methods. This method enables the C-RAN to avoid excessive overhead signaling. A low-complexity algorithm is designed to maximize the sum rate of all devices subject to the limits of backhaul capacity and base station transmit power. An adaptive algorithm has also been proposed to improve the robustness against channel uncertainty. Both theoretical and numerical analyses show that the exploitation of mobility information provides a new dimension to improve conventional transmission schemes for next-generation massive cooperative networks.

Energy Efficient Resource Allocation for Downlink Cooperative Non-Orthogonal Multiple Access Systems

Energy Efficient Resource Allocation for Downlink Cooperative Non-Orthogonal Multiple Access Systems

Optimal Relay Selection Schemes for Cooperative NOMA

This correspondence paper investigates relay selection (RS) schemes for cooperative downlink nonorthogonal multiple access (NOMA) networks with multiple relays. Two optimal RS schemes, termed as the two-stage weighted-max-min (WMM) and max-weighted-harmonic-mean (MWHM) schemes, are proposed for cooperative NOMA with fixed and adaptive power allocations (PAs) at the relays, respectively. Then, the outage probabilities of the two proposed RS schemes are analyzed, and their diversity gains are also determined. The provided simulation results show that the proposed optimal two-stage WMM and MWHM schemes outperform the existing suboptimal RS schemes for cooperative NOMA networks with fixed and adaptive PAs at the relays, respectively.