Non-orthogonal Multiple Access Scheme Research Articles

A Low-Complexity Coding Scheme for NOMA

This work focuses on exploiting the constructive interference among different users' data waveforms to introduce new coding and decoding techniques, which are specifically designed for nonorthogonal multiple access (NOMA) systems. In this article, a structured coding scheme is devised. In essence, the proposed technique focuses on finding a relationship between the sent users' data waveforms and then uses this relationship in the decoding process at the receiving destination. It is worth pointing out that the proposed coding and decoding techniques exhibit better performance and reduced the complexity compared with the conventional uncoded NOMA. The complexity order evaluation shows that the proposed scheme attains a reduction in the required number of the floating point operations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{5}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{6}\,N$</tex-math></inline-formula> at the second and third users, respectively, compared with that of the uncoded NOMA. Moreover, we have derived a closed-form expression for the bit error rate, which is verified using the Monte Carlo simulation. To demonstrate the practicality of the proposed system, the obtained results are compared with those of the uncoded and convolutional coding NOMA systems. Finally, the performance of the proposed system outperformed the conventional systems by an average of 5 dB in the case of two users and an average of 15 dB in the case of three users in the same work environment.

Three-dimensional power sparse code division non-orthogonal multiple access scheme with constellation pair mapping.

This paper proposes a three-dimensional power sparse code division non-orthogonal multiple access (3D-PSCD-NOMA) scheme with 3D constellation pair mapping. The proposed sparse code is based on a balanced incomplete block design (BIBD). Its correlation matrix performs the overall signal mapping of multi-user information. Power multiplexing is realized by overlaying multi-level power signals with different path losses through pair mapping. Compared with the conventional 2D standard square 32 Quadrature Amplitude Modulation (QAM), the proposed 3D constellation pair mapping can improve the constellation points' minimum Euclidean distance (MED) by 17.7%, which is beneficial for the performance of the system. Based on obtaining the optimal power distribution ratio (PDR) for different schemes, a 3D-PSCD-NOMA signal with a rate of 15.22 Gb/s over a 25 km single-mode fiber (SMF) is experimentally performed. The experimental results show that 3D-PSCD-NOMA has a clear superiority. At the same rate, 3D-PSCD-NOMA2 can obtain a sensitivity gain of about 1.6 dB and 1.9 dB over the conventional 2D constellation. Moreover, 3D-PSCD-NOMA reduces the system's peak-to-average power ratio (PAPR) by 1.3 dB. The difference in sensitivity of the system before and after sparse code is about 0.15 dB, and no significant degradation occurred. Due to its advantages in transmission performance, 3D-PSCD-NOMA is a potential solution for future optical access systems.

Dynamic multiple access based on deep reinforcement learning for Internet of Things

With the development of wireless communication technology, the rational use of spectrum resources utilizing efficient multiple access technology has become a research hotspot. The channel access strategy in dynamic spectrum access technology will directly affect the system’s spectrum utilization. Deep reinforcement learning is proposed to train users in the network to learn optimal channel access strategy to achieve reasonable allocation of spectrum resources on the channel. At the same time, the multiple access scheme adopted by users who have access to the channel will also affect the throughput of the system. Traditional multiple access schemes include Orthogonal Multiple Access scheme and Non-orthogonal Multiple Access (NOMA) scheme. In a dynamic environment, the multiple access scheme suitable for users on the channel is also dynamic. Therefore, DRL is introduced to help users learn the multiple access scheme selection strategy to maximize user throughput. Finally, we propose a dynamic multiple access algorithm based on deep reinforcement learning, which optimizes the channel access strategy and scheme selection strategy respectively, and improves the performance. The simulation results show that the proposed scheme is superior to other schemes in various scenarios, especially, the average throughput of the proposed scheme is about 0.8 Mbps and 0.5 Mbps higher than that of the FDMA scheme and NOMA scheme, respectively.

Experimental demonstration of a hybrid OFDMA/NOMA scheme for multi-user underwater wireless optical communication systems

In this work, a hybrid multiple access scheme for multi-user underwater wireless optical communication (UWOC) systems is proposed and presented. The scheme combines the respective advantages of orthogonal frequency-division multiple access (OFDMA) and non-orthogonal multiple access (NOMA) scheme to reduce the unfairness among users caused by the unique high-frequency fading characteristics of the underwater optical channel. Multi-verse optimizer (MVO) algorithm is further introduced for solving the nonlinear problem of user power allocation. Experimental results in different water quality environments demonstrate that the hybrid OFDMA/NOMA scheme with MVO effectively improves the communication performance of the established 4-user UWOC system compared to the pure NOMA scheme and the pure OFDMA scheme, and a system sum rate of 3.94 Gbit/s is achieved.

Performance analysis and optimization of multiple IIoT devices radio frequency energy harvesting NOMA mobile edge computing networks

In this day and age, the Industrial Internet of Things (IIoT) has been considered to revolutionize industrial manufacturing by capturing and accessing massive data sources with incredible speed and efficiency than before. Combined with it, Mobile Edge Computing (MEC) is a comprehensive Digital Transformation tendency to solve the problems Cloud computing faces. However, the fundamental challenges of energy and latency make deploying IIoT MEC networks difficult. Accordingly, this paper considers the efficient design of time allocation for successful computation probability (SCP) maximization for multiple energy-constrained mobile devices (MD) and multiple antennas access point (AP) in uplink radio frequency energy harvesting (RF EH) non-orthogonal multiple access (NOMA) IIoT network. Specifically, multiple MDs need to receive the energy and compute support of a MEC server placed in a multiple antenna wireless AP to complete the task immediately. Accordingly, a four-phase communication protocol is proposed to ensure system performance. The system follows the cluster head (CH) scheme based on the channel state information (CSI) to harvest RF energy from the AP. To ensure the highest system performance, we propose two algorithms for determining the optimal EH time for two CHs: SCPM-GSS and SCPM-GA. In addition, we derive the closed-form expressions for the SCP of the system and each CH. Monte Carlo simulations are used to verify the results of the analysis. The numerical results demonstrate the effects of crucial system parameters of our proposed NOMA scheme with those of conventional orthogonal multiple access (OMA) schemes. Furthermore, the proposed optimization algorithms allow the system to avoid outages like the random parameters setting approach and improve the SCP by 3 to 30% compared to the fixed parameters set when the transmit power is low and medium.

Improved Spectral Efficiency in STAR-RIS Aided Uplink Communication Using Rate Splitting Multiple Access

In this paper, a phase-shift coupled simultaneous transmitting/refracting and reflecting reconfigurable intelligent surface (STAR-RIS)-aided uplink (UL) rate-splitting multiple access (RSMA) system is investigated to achieve improved spectral efficiency. The considered UL RSMA system splits the rate for each user by dividing their message into multiple sub-messages and these sub-messages are transmitted to the base station (BS) via STAR-RIS as direct link between BS and user is absent. In particular, we formulate a resource allocation design problem which aim to maximize the overall rate-throughput of the considered system under the joint optimization of power allocation, decoding order, user-fairness and beamforming design at STAR-RIS for various operating modes of STAR-RIS modes, which is mixed- integer non-linear programming (MINLP). To solve the formulated non-convex complex problem, we first transform the original sum-rate maximization into its simplified form and then solved it using an alternating optimization algorithm where the sub-problems of power allocation and beamforming design under given decoding order are solved alternatively using general convex approximation and fractional programming approaches. Numerical simulation and computational complexity analysis validate that the proposed solution attains fast convergence. Moreover, the proposed RSMA scheme in STAR-RIS aided UL system outperforms the conventional nonorthogonal multiple access and orthogonal multiple access schemes in terms of overall rate-throughput and user-fairness.

THz-Enabled UAV Communications Using Non-Orthogonal Multiple Access

The fact that integrating the unmanned aerial vehicles (UAV) newfangled applications in the envisioned next generation (nextG) necessitates a considerable high throughput, makes terahertz (THz) band an emerging key enabler to support stringent requirements in the nextG wireless ecosystem. To fully utilize the potential of a synergy of UAV with THz frequency band, a THz-enabled UAV communication is scrutinized in this paper, where a single antenna UAV is serving the ground users by incorporating non-orthogonal multiple access (NOMA) scheme. Our objective is to maximize the total rate of all ground users by jointly optimizing bandwidth allocation, power allocation, and UAV deployment in THz communication systems. The formulated max-sum rate optimization problem is non-convex, which makes it hard to solve optimally. Therefore, to cope with the aforementioned puzzle, we adopt an inner convex approximation-based path-following approach that considers a Joint Optimization of Power, Bandwidth allocation, and UAV's Deployment (JOPBD) by utilizing NOMA scheme. Furthermore, a comparison of our proposed JOPBD algorithm, with the orthogonal multiple access, and other baseline schemes is conducted. Then, the numerical simulations are carried out to reveal the impact of our proposed approach, and also to confirm its significance for the UAV operating in THz band.

Reliability analysis for NOMA‐based UAV assisted short packet communication

AbstractThis paper introduces the short packet transmission in non‐orthogonal multiple access (NOMA)‐based unmanned aerial vehicle (UAV) assisted relay communication system. Short packet transmission has considerable potential to decrease the transmission latency of UAV communication, and NOMA can effectively enhance the spectrum efficiency and fairness. To improve the reliability of the system, an effective packet error rate (PER) minimization problem within short packet transmission is proposed by jointly optimizing the packet length, UAV placement, and power allocation under the reliability requirement and total power constraints. To address the intricate PER minimization problem, the optimization problem is firstly decomposed into three sub‐problems, and the corresponding monotonicity and convexity are analyzed, respectively. Then, an overall iterative optimization algorithm for PER minimization based on alternating direction method of multipliers algorithm and optimal solution algorithm is formulated by solving the three sub‐problems in an iterative manner. Simulation results validate the effectiveness and convergence of the proposed NOMA scheme and overall iterative optimization algorithm, respectively.

Capacity analysis of infrastructure-to-vehicle visible light communication with an optimized non-orthogonal multiple access scheme

Capacity analysis of infrastructure-to-vehicle visible light communication with an optimized non-orthogonal multiple access scheme

NOMA or OMA in Delay-QoS Limited Satellite Communications: Effective Capacity Analysis

In this paper, we theoretically study the achievable capacity of orthogonal and non-orthogonal multiple access (OMA and NOMA) schemes in supporting downlink satellite communication networks. Considering that various satellite applications have different delay quality-of-service (QoS) requirements, the concept of effective capacity is introduced as a delay-guaranteed capacity metric to represent users’ various delay requirements. Specifically, the analytical expressions of effective capacities for each user achieved with the NOMA and OMA schemes are first studied. Then, approximated effective capacities achieved in some special cases, exact closed-form expressions of users’ achievable effective capacity, and the capacity difference between NOMA and OMA schemes are derived. Simulation results are finally provided to validate the theoretical analysis and show the suitable limitations of the NOMA and OMA schemes, such as the NOMA scheme is more suitable for users with better channel quality when transmit signal-to-noise (SNR) is relatively large, while it is suitable for users with worse link gain when transmit SNR is relatively small. Moreover, the influences of delay requirements and key parameters on user selection strategy and system performance are also shown in the simulations.

NON-ORTHOGONAL MULTIPLE ACCESS SCHEMES SURVEY: AN OVERVIEW OF NON-ORTHOGONAL MULTIPLE ACCESS TECHNIQUES

Non-Orthogonal Multiple Access (NOMA) is a promising technology that can significantly improve the performance of wireless communication systems, especially in applications with a high number of users and limited spectral resources. NOMA enables simultaneous transmission and reception of multiple signals at the same time and frequency resources. NOMA can be implemented using different methods, including Power Domain NOMA (PD-NOMA) and Code Domain NOMA (CD-NOMA). The implementation of NOMA requires advanced signal processing techniques and can be challenging in some scenarios. However, with the advancement of technology, NOMA is becoming more practical and is expected to play a significant role in the future of wireless communication systems. This paper will discuss what NOMA and NOMA schemes are. These schemes will be compared in terms of their benefits and drawbacks, and it will be explained which one performs better.

DRL-Based Resource Allocation in Remote State Estimation

Remote state estimation where sensors send their measurements of distributed dynamic plants to a remote estimator over shared wireless resources is essential for mission-critical applications of Industry 4.0. Existing algorithms on dynamic radio resource allocation for remote estimation systems assumed oversimplified wireless communications models and can only work for small-scale settings. In this work, we consider remote estimation systems with practical wireless models over the orthogonal multiple-access and non-orthogonal multiple-access schemes. We derive necessary and sufficient conditions under which remote estimation systems can be stabilized. The conditions are described in terms of the transmission power budget, channel statistics, and plants’ parameters. For each multiple-access scheme, we formulate a novel dynamic resource allocation problem as a decision-making problem for achieving the minimum overall long-term average estimation mean-square error. Both the estimation quality and the channel quality states are taken into account for decision making. We systematically investigated the problems under different multiple-access schemes with large discrete, hybrid discrete-and-continuous, and continuous action spaces, respectively. We propose novel action-space compression methods and develop advanced deep reinforcement learning algorithms to solve the problems. Numerical results show that our algorithms solve the resource allocation problems effectively and provide much better scalability than the literature.

Performance Analysis of NOMA-Based Hybrid Satellite-Terrestrial Relay Networks With CCI

Hybrid satellite-terrestrial relay networks (HSTRNs) which exploit relay cooperative technology in the integrated system of satellites and terrestrial base stations (BSs) are expected to offer enhanced transmission performance benefited from the spatial gain of independent fading paths. To enable multi-user accessing and resource sharing among users, non-orthogonal multiple access (NOMA) technique can be applied in HSTRNs. In this paper, we consider a NOMA-based HSTRN where a satellite transmits signals to a relay base station (RBS) and a destination ground station (DGS), and RBS also serves a cellular user (CU) and DGS simultaneously by leveraging NOMA scheme. We assume that the satellite shares spectrum with a number of cellular small BSs (SBSs), hence SBSs will cause co-channel interference (CCI) to DGS, RBS and CU. We examine the transmission characteristics of the satellite and terrestrial links, and derive the closed-form expressions of the outage probability (OP) and average symbol error rate (ASER) of DGS and CU, respectively. Specially, we consider the effect of perfect and imperfect successive interference cancellation (SIC) on the ASER performance of CU. Then, considering the stochastic characteristics of satellite links and CCI, we analyze the mean energy efficiency (MEE) of the satellite and propose an optimal power allocation scheme which maximizes the MEE of the satellite and achieves system performance optimization. Simulation results demonstrate the effectiveness of the theoretical analysis and the proposed power allocation scheme.

Performance enhancement of nonorthogonal multiple access systems by multiple UAVs and RISs

This article proposes a combination of multiple unmanned aerial vehicles (UAVs) and multiple reconfigurable intelligent surfaces (RISs) to assist non-orthogonal multiple access (NOMA) systems. In particular, multiple UAVs mounted multiple RISs (UAVs-RISs) fly at convenient positions to improve the quality of service at multiuser adopting the NOMA scheme. The expressions of outage probability (OP) and throughput of UAVs-RISs-NOMA systems are derived over propagation environments recommended for the fifth and beyond generations (5G/B5G) of wireless communications. Besides general forms, the other forms of outage and throughput expressions in the case of there are only two users are also derived to clarify the contributions of the system parameters in the derived formulas. Monte-Carlo simulations are conducted to authenticate the exactness of the derived expressions. Numerical illustrations clarify the advantages of UAVs-RISs for improving the performance of NOMA systems. Particularly, the OP of the UAVs-RISs-NOMA systems is greatly lower than the OP of classical NOMA systems without UAVs-RISs. In other words, by utilizing UAVs-RISs, the OP of NOMA systems is dramatically reduced. In the meanwhile, the throughput of UAVs-RISs-NOMA systems is significantly higher than that of classical NOMA systems. As a result, the usage of UAVs-RISs can considerably reduce the transmit power of the base station. Besides the advantages of UAVs-RISs, the system behaviors under the effects of the environmental characteristics, carrier frequencies of Wi-Fi communications, altitudes of UAVs-RISs and totals of reflecting elements (REs) are deeply determined. Based on these behaviors, some effective solutions such as an increase in the total of REs, using suitable transmit power and choosing appropriate carrier frequency can be utilized for improving the performance of UAVs-RISs-NOMA systems.

Adaptive Aquila optimized relay selection and power allocation in CR-NOMA model

Cooperative communication combining non-orthogonal multiple access (NOMA) and cognitive radio is a rapidly growing technique for wireless networks and beyond 5G Still, security is considered one of the primary issues due to overheard confidential details in wireless transmission platforms. Consequently, the replacement of encryption-based strategies for security must be done at the physical layer. The proposed method uses an enhanced Aquila optimization algorithm (EAO) to replace encryption methods to select the best joint relay and power allocation (PA). The method undergoes two stages to deliver the message to the secondary users (Ss). The first stage is the message transmitted from the secondary base station (BS) to the relay, and the second stage is relaying the message to the secondary users. Best joint relays are selected based on two objective functions to maximize throughput and the secrecy sum rate (SSR) with two factors delay and secrecy rate of CR-NOMA. To enhance the exploration and exploitation stages of the proposed algorithm, representative-based hunting (RH) is employed. The effectiveness of the proposed method is analyzed with other existing baselines on various performance metrics. The results showed that the proposed method performs well due to the inclusion of the NOMA strategy and maximizes the throughput and SSR of the network.

SCMA-Enabled Multi-Cell Edge Computing Networks: Design and Optimization

Multi-access edge computing (MEC) is regarded as a promising approach for providing resource-constrained mobile devices with computing resources through task offloading. Sparse code multiple access (SCMA) is a code-domain non-orthogonal multiple access (NOMA) scheme that can meet the demands of multi-cell MEC networks for high data transmission rates and massive connections. In this paper, we propose an optimization framework for SCMA-enabled multi-cell MEC networks. The joint resource allocation and computation offloading problem is formulated to minimize the system cost, which is defined as the weighted energy cost and latency. Due to the nonconvexity of the proposed optimization problem induced by the coupled optimization variables, we first propose an algorithm based on the block coordinate descent (BCD) method to iteratively optimize the transmit power and edge computing resources allocation by deriving closed-form solutions, and further develop an improved low-complexity simulated annealing (SA) algorithm to solve the computation offloading and multi-cell SCMA codebook allocation problem. To solve the problem of partial state observation and timely decision-making in long-term optimization environment, we put forward a multiagent deep deterministic policy gradient (MADDPG) algorithm with centralized training and distributed execution. Furthermore, we extend the framework to the partial offloading case and propose an algorithm based on alternating convex search for solving the task offloading ratio. Numerical results show that the proposed multi-cell SCMA-MEC scheme achieves lower energy consumption and system latency in comparison to the orthogonal frequency division multiple access (OFDMA) and power-domain (PD) NOMA techniques.

Sensing and Secure NOMA-Assisted mMTC Wireless Networks

Throughout this study, a novel network model for massive machine-type communications (mMTC) is proposed using a compressive sensing (CS) algorithm and a non-orthogonal multiple access (NOMA) scheme. Further, physical-layer security (PLS) is applied in this network to provide secure communication. We first assume that all the legitimate nodes operate in full-duplex mode; then, an artificial noise (AN) signal is emitted while receiving the signal from the head node to confuse eavesdroppers (Eve). A convex optimization tool is used to detect the active number of nodes in the proposed network using a sparsity-aware maximum a posteriori (S-MAP) detection algorithm. The sensing-aided secrecy sum rate of the proposed network is analyzed and compared with the sum rate of the network without sensing, and the closed-form expression of the secrecy outage probability of the proposed mMTC network is derived. Finally, our numerical results demonstrate the impact of an active sensing algorithm in the proposed mMTC network; improvement in the secrecy outage of the proposed network is achieved through increasing the distance of the Eve node.

Performance Analysis of Anti-Interference Cooperative NOMA System for Aviation Data Links

In collaborative combat operations, the challenges posed by communication adversities in aviation data links have become increasingly conspicuous. Ensuring the reliable connectivity of data links has thus emerged as a critical issue, particularly in light of growing interference effects on communication link outage. To address this challenge, this paper proposes a cooperative non-orthogonal multiple access (NOMA) technology that aims to enhance interference tolerance and strengthen stable communication capabilities in data links. To achieve these goals, an anti-interference collaborative NOMA system model applicable to aviation data links is established, and the anti-interference performance of collaborative NOMA technology is analyzed under Rice fading channel conditions. The analysis centers on the system’s outage probability, for which a closed-form expression is derived. Numerical analysis methods are employed to calculate and solve the expression, while simulation experiments are conducted to analyze the effect of factors such as transmission power, cooperative forwarding power, interference power, communication distance, and allocation coefficients on the system’s outage probability. The results show that the aviation data link system using a collaborative NOMA scheme has better anti-interference performance than a non-collaborative scheme, and adjusting the above parameters can effectively improve the system’s stable communication performance.

An Enhanced Probabilistic-Shaped SCMA NOMA for Wireless Networks

The future digital evolution poses challenges that need to be spectral and energy-efficient, as well as highly reliable and resilient. The non-orthogonal multiple access (NOMA) accomplishes massive connectivity, spectral efficiency, effective bandwidth utilization, and low latency. The proposed work involves the code domain NOMA scheme called Sparse Code Multiple Access (SCMA) which provides shaping gain through multi-dimensional constellation and the best performance in terms of bit error rate (BER). It achieves overloading of users through the non-orthogonal allocation of resources which enhances the spectral efficiency and serves more users. The shaping gain can be further improved by reducing the BER and enhancing the capacity of the channel through constellation shaping. This work employs a probabilistic-shaped (PS) constellation where each symbol is transmitted with different probabilities which achieves a reduction of average symbol power and forward error correction (FEC) through channel coding using polar codes which aid in energy efficiency. The output is two-dimensionally spread over Orthogonal Frequency Code Division Multiplexing (OFCDM) subcarriers to achieve a flexible transmission rate through a variable spreading factor. Computer simulations showed better BER performance under AWGN and Rayleigh channels with remarkable gain in SNR which paves the way for future applications in Fifth Generation (5G) beyond networks.

Low-Latency Hybrid NOMA-TDMA: QoS-Driven Design Framework

Enabling ultra-reliable and low-latency communication services while providing massive connectivity is one of the major goals to be accomplished in future wireless communication networks. In this paper, we investigate the performance of a hybrid multi-access scheme in the finite blocklength (FBL) regime that combines the advantages of both non-orthogonal multiple access (NOMA) and time-division multiple access (TDMA) schemes. Two latency-sensitive application scenarios are studied, distinguished by whether the queuing behaviour has an influence on the transmission performance or not. In particular, for the latency-critical case with one-shot transmission, we aim at a certain physical-layer quality-of-service (QoS) performance, namely the optimization of the reliability. And for the case in which queuing behaviour plays a role, we focus on the link-layer QoS performance and provide a design that maximizes the effective capacity. For both designs, we leverage the characterizations in the FBL regime to provide the optimal framework by jointly allocating the blocklength and transmit power of each user. In particular, for the reliability-oriented design, the original problem is decomposed and the joint convexity of sub-problems is shown via a variable substitution method. For the effective-capacity-oriented design, we exploit the method of Lagrange multipliers to formulate a solvable dual problem with strong duality to the original problem. Via simulations, we validate our analytical results of convexity/concavity and show the advantage of our proposed approaches compared to other existing schemes.