NOMA Networks Research Articles

Machine Learning for Resource Management in Cellular and IoT Networks: Potentials, Current Solutions, and Open Challenges

Internet-of-Things (IoT) refers to a massively heterogeneous network formed through smart devices connected to the Internet. In the wake of disruptive IoT with a huge amount and variety of data, Machine Learning (ML) and Deep Learning (DL) mechanisms will play a pivotal role to bring intelligence to the IoT networks. Among other aspects, ML and DL can play an essential role in addressing the challenges of resource management in large-scale IoT networks. In this article, we conduct a systematic and in-depth survey of the ML- and DL-based resource management mechanisms in cellular wireless and IoT networks. We start with the challenges of resource management in cellular IoT and low-power IoT networks, review the traditional resource management mechanisms for IoT networks, and motivate the use of ML and DL techniques for resource management in these networks. Then, we provide a comprehensive survey of the existing ML- and DL-based resource management techniques in wireless IoT networks and the techniques specifically designed for HetNets, MIMO and D2D communications, and NOMA networks. To this end, we also identify the future research directions in using ML and DL for resource allocation and management in IoT networks.

Energy Efficiency Maximization in Downlink Multi-Cell Multi-Carrier NOMA Networks With Hardware Impairments

In this paper, we investigate energy efficiency (EE) maximization in multicell multicarrier non-orthogonal multiple access (MCMC-NOMA) networks with hardware impairments (HIs). We formulate the optimization problem as a mixed integer nonlinear NP-hard problem, which is difficult to solve efficiently. To solve this problem, we decompose it into two subproblems. The first subproblem is the user and base station (BS) association and subchannel assignment problem, where binary whale optimization algorithm (BWOA) is proposed to handle it. For the second subproblem of the non-convex power allocation problem, successive pseudo-convex approximation (SPCA) is employed to establish the problem’s pseudo-convexity. The approximate problem is separable into a sequence of equivalent problems that can be easier to solve. Each problem of the obtained sequence has a stationary point solution and is guaranteed to converge. The simulation results demonstrate that the proposed algorithm achieves a performance comparable to that of the successive lower bound maximization (SLBM) algorithm and outperforms both fractional transmit power allocation (FTPA) benchmark for NOMA and the conventional orthogonal multiple access (OMA).

Clustering and Auction-Based Power Allocation Algorithm for Energy Efficiency Maximization in Multi-Cell Multi-Carrier NOMA Networks

In this paper, we investigate the energy efficiency (EE) maximization in multi-cell multi-carrier non-orthogonal multiple access (MCMC-NOMA) networks. To achieve this goal, an optimization problem is formulated then the solution is divided into two parts. First, we investigate the inter-cell interference mitigation and then we propose an auction-based non-cooperative game for power allocation for base stations. Finally, to guarantee the rate requirements for users, power is allocated fairly to users. The simulation results show that the proposed scheme has the best performance compared with the existing NOMA-based fractional transmit power allocation (FTPA) and the conventional orthogonal frequency division multiple access (OFDMA).

Cooperative Overlay Cognitive Radio NOMA Network with Channel Errors and Imperfect SIC

Cooperative Overlay Cognitive Radio NOMA Network with Channel Errors and Imperfect SIC

Cooperative Dual Relay Overlay CR NOMA Network with Outdated CSI

Cooperative Dual Relay Overlay CR NOMA Network with Outdated CSI

Downlink NOMA Networks With Hybrid Long-Packet and Short-Packet Communications in Flat Rayleigh Fading Channels

In this letter, we propose a downlink nonorthogonal multiple access network with hybrid long-packet communications (for a central user) and short-packet communications (for a cell-edge user). The outage probability of the central user and average block error rate (BLER) of the cell-edge user in flat Rayleigh fading channels are theoretically derived. Furthermore, we provide the asymptotic outage probability and average BLER when the signal-to-noise ratio (SNR) is high. Numerical results illustrate that both the analytical outage probability of the central user and the analytical average BLER of the cell-edge user match the simulation results.

Physical Layer Security in Cognitive Radio Inspired NOMA Network

This paper investigates physical layer security (PLS) in cognitive radio inspired non-orthogonal multiple access (CR-NOMA) networks with multiple primary and secondary users. To manage the interferences among the users and guarantee the quality of services of primary users, a new secure NOMA transmission strategy is designed, where the primary and secondary users are paired according to their channel gains, respectively, and power-domain NOMA is employed to transmit the signal. Then, the closed-form expressions for connection outage probability, secrecy outage probability, and effective secrecy throughput are derived for the primary users over Nakagami- $m$ fading channels when the secondary users are considered as eavesdroppers. Typically, the secrecy performance can be improved by pairing the primary users with best channel gains or reducing the number of secondary users. In addition, we also investigate the performances of secondary users by deriving the closed-form expressions for throughput of secondary network. Furthermore, simulations are conducted to verify our analysis results and provide insights into the impact of the parameters on system performance.

Performance Analysis of Relay Selection in Cooperative NOMA Networks

In this letter, we investigate the relay selection (RS) problem in cooperative non-orthogonal multiple access networks, where one base station communicates with two paired users with different priorities through multiple relays. A novel two-stage RS scheme is proposed to satisfy the quality-of-service requirements of both users by considering the employment of the instantaneous channel state information in the user ordering. We derive a closed-form expression of the outage probability and obtain the diversity order for the proposed scheme. The simulation results show that the proposed RS scheme achieves a lower outage probability than the existing RS schemes.

Joint relay selection and energy‐efficient power allocation strategies in energy‐harvesting cooperative NOMA networks

AbstractIn this paper, the problem of joint relay selection and energy‐efficient power allocation (J‐RS‐EE‐PA) in energy‐harvesting cooperative nonorthogonal multiple‐access networks is considered. In particular, a base station communicates with multiple users via a selected energy‐harvesting relay, such that energy efficiency (EE) is maximized, subject to quality‐of‐service constraints. Four different EE power allocation strategies are considered, namely, global energy efficiency, minimum energy efficiency, product energy efficiency, and sum energy efficiency. For all the aforementioned strategies, the J‐RS‐EE‐PA problem happens to be nonconvex and, thus, is computationally prohibitive. In turn, the J‐RS‐EE‐PA problem is decoupled into two subproblems: (1) relay selection and (2) energy‐efficient power allocation. Different relay selection strategies are explored, and then, computationally efficient algorithms are devised to optimally solve the different EE power allocation strategies for the selected relay. In addition, a low‐complexity solution procedure is proposed to solve the J‐RS‐EE‐PA problem. Simulation results are presented to evaluate the resulting EE of the different relay selection and power allocation strategies in comparison to the formulated J‐RS‐EE‐PA problem. More importantly, the proposed solution procedure is shown to be superior to the different explored relay selection strategies as well as yielding the global optimal solution of the J‐RS‐EE‐PA problem for the global energy efficiency, minimum energy efficiency, product energy efficiency, and sum energy efficiency strategies, while satisfying quality‐of‐service requirements.

Mode Selection Between Index Coding and Superposition Coding in Cache-Based NOMA Networks

By analytically showing that index coding (IC) is more power efficient than superposition coding (SC) when appropriate caching contents are available for a pair of users, we propose a sub-optimal joint user clustering and power allocation scheme for a single-cell downlink non-orthogonal multiple access network with caching memory at the receivers that alternate between IC and SC. Simulation studies demonstrate that the proposed scheme significantly reduces the transmission power when compared with the benchmark scheme that only allows SC.

Joint relay selection and max‐min energy‐efficient power allocation in downlink multicell NOMA networks: A matching‐theoretic approach

AbstractIn this paper, the problem of joint relay selection and max‐min energy‐efficient power allocation (J‐RS‐MMEE‐PA) in downlink multicell nonorthogonal multiple access (NOMA) networks is studied. In particular, the goal is to perform relay selection for each cellular user within each cell, so as to achieve max‐min energy efficiency while satisfying quality‐of‐service (QoS) constraints. However, the formulated J‐RS‐MMEE‐PA problem happens to be nonconvex (ie, computationally intensive). In turn, a solution procedure for max‐min energy‐efficient power allocation is devised to determine the energy efficiency of each user per potential relay while meeting the target minimum rate per user. After that, the relay selection problem is modeled as a student‐project allocation with preferences over projects matching problem. A polynomial‐time complexity stable matching (SM) algorithm is proposed, which takes into account the maximum number of users that can select a relay as well as the number of users that can be associated with a base station. However, the proposed SM algorithm can only guarantee an SM size that is at least half the size of the maximum “optimal” cardinality SM. Thus, the improved SM (I‐SM) algorithm with polynomial‐time complexity is devised, so as to guarantee an SM size that is at least two‐thirds of that of the optimal matching. Lastly, simulation results are presented to compare the proposed matching algorithms to the J‐RS‐MMEE‐PA scheme, where it has been shown that the I‐SM algorithm is superior to its SM counterpart and yields comparable energy efficiency per cellular user to the J‐RS‐MMEE‐PA scheme while satisfying QoS constraints.

Security Energy Efficiency Maximization for Two-Way Relay Assisted Cognitive Radio NOMA Network With Self-Interference Harvesting

The security energy efficiency (SEE) is investigated in a two way-full duplex (TW-FD) relay assisted cognitive radio non-orthogonal multiple access (CR-NOMA) networks. In order to improve system energy efficiency, the self-interference (SI) of FD can be regarded as a potential source for relay to harvest energy. Our objective is to maximize security energy efficiency of the secondary user (SU) system subject to harvested energy and the quality of service (QoS) of the users. Specifically, the multi-objective optimization problem is decomposed into three subproblems, i.e., the optimization of transmitting covariance matrix, power allocation, and power splitting ratio. The problem with optimizing transmit covariance matrix is non-convex, hence the semi-determined relaxation algorithm based on the first-order Taylor series expansion function is proposed to solve it. Besides, the multi-objective iterative algorithm (MOIA) is further proposed to achieve the joint optimal solution. The simulation results show that under the same constrains of power allocation and energy harvested, the proposed scheme of two way-full duplex self-interference harvest has significant performance gain on security energy efficiency over the self-interference cancellation.

Joint Admission Control and Resource Allocation for Multi-Carrier Uplink NOMA Networks

In this letter, we study the maximum access problem (MAP) for uplink networks with non-orthogonal multiple access technique. Specifically, the MAP is formulated as a mixed integer programming problem with admission control, user clustering, channel assignment, and power control taken into account. To deal with this challenging problem, we first recast it as the maximum independent set (MIS) problem in graph theory. Then, we propose an efficient algorithm to solve this MIS problem in a low complexity manner. Finally, simulation results indicate that our algorithm can greatly improve the number of supported users compared to other schemes. The performance of our algorithm under different channel conditions and non-uniform distributions of users is also investigated.

Outdated relay selection for UAV-enabled networks with cooperative NOMA

The outdated relay selection algorithm for UAV-enabled cooperative amplify-and-forward NOMA networks is investigated in this paper. The impacts of the system parameters such as the outdated coefficient, the transmission SNR, the relays’ number and the average channel gain are evaluated by the exact analytical expressions as well as the asymptotic results on the outage probability. Based on the asymptotic expressions, we find that the diversity order of the system remains one, regardless of the relays’ number and the average channel gain. Simulation results are provided to confirm the theoretical analysis.

QoE-Based Resource Allocation for Multi-Cell NOMA Networks

Quality of experience (QoE) is an important indicator in the fifth generation (5G) wireless communication systems. For characterizing user-base station (BS) association, subchannel assignment, and power allocation, we investigate the resource allocation problem in multi-cell multicarrier non-orthogonal multiple access (MC-NOMA) networks. An optimization problem is formulated with the objective of maximizing the sum mean opinion scores (MOSs) of users in the networks. To solve the challenging mixed integer programming problem, we first decompose it into two subproblems, which are characterized by combinational variables and continuous variables, respectively. For the combinational subproblem, a 3-D matching problem is proposed for modeling the relation among users, BSs, and subchannels. Then, a two-step approach is proposed to attain a suboptimal solution. For the continuous power allocation subproblem, the branch and bound approach is invoked to obtain the optimal solution. Furthermore, a low complexity suboptimal approach based on successive convex approximation techniques is developed for striking a good computational complexity-optimality tradeoff. Simulation results reveal that: 1) the proposed NOMA networks is capable of outperforming conventional orthogonal multiple access networks in terms of QoE and 2) the proposed algorithms for sum-MOS maximization can achieve significant fairness improvement against the sum-rate maximization scheme.

Exploiting Opportunistic Scheduling for Physical‐Layer Security in Multitwo User NOMA Networks

In this paper, we address the opportunistic scheduling in multitwo user NOMA system consisting of one base station, multinear user, multifar user, and one eavesdropper. To improve the secrecy performance, we propose the users selection scheme, called best‐secure‐near‐user best‐secure‐far‐user (BSNBSF) scheme. The BSNBSF scheme aims to select the best near‐far user pair, whose data transmission is the most robust against the overhearing of an eavesdropper. In order to facilitate the performance analysis of the BSNBSF scheme in terms of secrecy outage performance, we derive the exact closed‐form expression for secrecy outage probability (SOP) of the selected near user and the tight approximated closed‐form expression for SOP of the selected far user, respectively. Additionally, we propose the descent‐based search method to find the optimal values of the power allocation coefficients that can minimize the total secrecy outage probability (TSOP). The developed analyses are corroborated through Monte Carlo simulation. Comparisons with the random‐near‐user random‐far‐user (RNRF) scheme are performed and show that the proposed scheme significantly improves the secrecy performance.

Joint User and Relay Selection for Cooperative NOMA Networks

This paper investigates the joint user and relay selection algorithm for cooperative non-orthogonal multiple access networks, where multiple users transmit messages to two destinations by utilizing multiple amplify-and-forward relays. To improve the outage performance of system, an optimal selection criterion is proposed at the user-relay pairs. We derive the closed-form analytical expressions on the outage probability, as well as the asymptotic expressions for large transmission power. Based on the derived analytical expressions, the effect of the number of relays and the target data rate on the outage performance is revealed. Results indicate that when the target data rate becomes small enough, the diversity order of the outage probability equals to the number of relays, while the target data rate grows without bound, the outage probability achieves one.