Non-orthogonal Multiple Access Design Research Articles

On performance analysis of non-orthogonal multiple access downlink for cellular-connected unmanned aerial vehicle relaying assisted vehicle-to-everything system

This paper presents the unmanned aerial vehicle (UAV) relays’ assisted vehicle-to-everything (V2X) network to implement the internet of things (IoT) systems with improvement in the coverage area. Such a network benefits from many advantages of the non-orthogonal multiple access (NOMA) scheme. We have implemented a decode-and-forward (DF) scheme for these UAVs. Then, we characterize the channels as Nakagami-m fading to evaluate the performance of the system. We derive closed-form expressions of outage probability (OP), ergodic capacity (EC), and throughput. The results show that the performance of the system depends on the transmitted signal-to-noise ratio (SNR) at the base station and the heights of the UAV relays. Target rate and power allocation factors are two main parameters that can be adjusted to achieve better performance. The results also compare to the system without UAV and OMA technique that shows the advantages of deploying UAV-assisted NOMA. Therefore, the design of NOMA for UAV relay-assisted V2X systems provides sufficient demand. The simulation results verified the effectiveness of the proposed UAV network and the precision of the theoretical analysis.

A taxonomy on power optimization techniques for fifth-generation heterogenous non-orthogonal multiple access networks

Non-orthogonal multiple access (NOMA) is an anticipated technology for fifth-generation networks for increasing mass connectivity, spectrum efficiency, user-fairness, and higher capacity. NOMA allows end-clients to share indistinguishable radio resources such as spreading code, subcarrier, and time slots simultaneously. Thus, the main challenge involved in conceptualizing effective NOMA design is selection of resource allocation (i.e., user clustering, power allocation, and quality-of-service (QoS) assurance) algorithms. NOMA can be easily integrated with current fifth-generation multi-access methodologies. In this survey paper, the NOMA methodologies are discussed, and provide an overview of the methodologies and algorithms designed for optimizing power allocation, interference management, and network selection management in the heterogenous multiple carrier NOMA. The survey highlights the current limitation of the existing resource provisioning framework and presents a solution to overcome the current limitation.

Robust Beamforming Design for an IRS-Aided NOMA Communication System With CSI Uncertainty

Intelligent reflecting surface (IRS) is a promising technology that provides high throughput in future communication systems and is compatible with various communication techniques, such as non-orthogonal multiple-access (NOMA). This paper studies the downlink transmission of IRS-assisted NOMA communication, considering the practical case of imperfect channel state information (CSI). Aiming to maximize the system sum rate, a robust IRS-aided NOMA design is proposed to jointly find the optimal beamforming vector for the access point and the passive reflection matrix for the IRS. This robust design is realised using the penalty dual decomposition (PDD) scheme, and it is shown that the results have a close performance to their upper bound obtained from the corresponding perfect CSI scenario. The presented method is compatible with both continuous and discrete phase shift elements of the IRS. Our findings show that the proposed algorithms, for both continuous and discrete IRS, have low computational complexity compared to other schemes in the literature. Furthermore, we conduct a performance comparison between the IRS-aided NOMA and the IRS-aided orthogonal multiple access (OMA). This comparison shows that robust beamforming techniques are crucial for the system to reap the advantages of IRS-aided NOMA communication in the presence of CSI uncertainty.

Precoder Based Transceivers Design for Non-Orthogonal Multiple Access Mixed Numerologies

Orthogonal Frequency Division Multiplexing (OFDM) based mixed numerology scheme and Non-Orthogonal Multiple Access (NOMA) are the two important key features of 5G radio standard capable of handling diversified service requirements. However, the mixed numerology scheme suffers from an inherent problem called Inter Numerology Interference (INI) that arises due to non-orthogonality issue between any two numerologies, whereas NOMA suffers from potential Bit Error Rate (BER). In this research work, transmitter architecture based on windowing and pre-coding techniques to mitigate the INI and two receiver architectures based on the principle of Successive Interference Cancellation (SIC) and Combined Maximum Likelihood (CDML) decoding are proposed for optimal decoding of the information. The proposed system model is designed to operate under mixed numerology NOMA scenario. The BER performance analysis is done for both the receivers and compared with each other and the conclusive remarks are drawn.

Beamforming Design for Active IOS Aided NOMA Networks

This letter investigates a new active intelligent omni-surface (IOS) aided non-orthogonal multiple access (NOMA) network. In particular, simple active devices are introduced into the IOS to overcome the “double-fading” effect. A sum achievable rate optimization problem is formulated, where the beamforming vector at the base station and the active IOS coefficients are jointly optimized while satisfying the quality of service requirements of the users. Then, an efficient alternating optimization algorithm is developed to obtain the stationary point solution. Numerical results demonstrate the performance advantage of the proposed active IOS aided NOMA design.

INTELLIGENT OPTIMIZATION OF MULTIPLE ACCESS INFOCOMMUNICATION NETWORKS

The methods of multiple access with multiplexing of resources are studied and the advantages and disadvantages of orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA) are considered. A comparative analysis of data transmission schemes in the radio network was also performed, taking into account resource planning, in particular: transmission with service information and transmission without service information. The structure of the NOMA uplink receiver based on OFDM signals is proposed. The peculiarities of providing supermassive connection within limited radio resources on the basis of grantless access using NOMA have been studied. At the same time, methods of solving the problems inherent in the current application of GF-transmission and NOMA in the implementation of supermassive connection to the access network based on 6G technology were considered. Prospects for the introduction of an artificial intelligence transmitter based on a multiple access transmission scheme with low cost, low PAPR, low delay, high reliability and wide connectivity are determined. And features of artificial intelligence receiver design using artificial intelligence / machine learning techniques that can play a role in facilitating MUD design for NOMA are also considered.

Optimal finite alphabet scheme for NOMA uplink channels

AbstractThe design of an optimal non‐orthogonal multiple access (NOMA) transmission scheme with finite alphabet inputs for a typical two‐user uplink wireless communication system is investigated in which each terminal is equipped with a single antenna. Each of the two users utilises a four quadrature amplitude modulation (4‐QAM) constellation to transmit information data to a common base station, and the receiver employs a maximum likelihood (ML) detector to jointly estimate both transmitted signals. Assuming the availability of channel state information at both the transmitters and the receiver, it is aimed to design a pair of scalar beamformers for the two users such that the minimum Euclidean distance between elements of the received sum‐constellation is maximised subject to the power constraints on the users. A thorough consideration of all the different conditions results in the derivation of a closed‐form optimal beamformer design. As well, examination of the construction of sum‐constellation resulted from the optimum design directly leads to the unique decoding of the original transmitted signal of each user. To facilitate practical implementation, a fast decoding procedure of the optimum NOMA scheme is further developed. The corresponding theoretic probability of ML detection error is also derived. The theoretical development of an optimum sum‐constellation for the basic 2‐user 4‐QAM system provides a solid platform for the derivation of an optimum sum‐constellation for a K‐user and/or M‐QAM system. Indeed, a simple development of the basic sum‐constellation map facilitates such extensions. Numerical simulations not only demonstrate that the performance of the fast decoder agrees closely with the theoretical analysis, but also verify that it is superior in performance to other existing NOMA designs for the same system under high signal‐to‐noise ratio.

Exploiting hybrid non‐orthogonal multiple access in satellite–terrestrial systems with randomly deployed users

In this letter, a hybrid non-orthogonal multiple access (NOMA) scheme for satellite–terrestrial systems is proposed, which is capable of integrating both power domain NOMA (PD-NOMA) and code domain NOMA (CD-NOMA) design modes. The stochastic geometry method is considered to model the position of the terrestrial NOMA user. Specifically, the closed-form expressions of exact outage probability with imperfect interference cancellation are derived. In order to get more insights, the asymptotic outage probabilities for high SNR conditions are also discussed. Numerical results are provided to confirm the validity of theoretical analysis and reveal the effects of critical parameters on system performance.

Design and Analysis of NOMA With Adaptive Modulation and Power Under BLER Constraints

In this work, we derive closed-form expressions for the throughput of non-orthogonal multiple access (NOMA) and use the expressions to maximize the throughput. The design considers a packet-based transmission where the base station optimizes the modulation orders and power coefficients while satisfying the block error rate requirement for each user. The optimization problem is solved using integer and mixed-integer programming, where the computational complexity is reduced using an efficient stopping criterion, segment-line search, and quantized signal to noise ratios (SNRs). The analytical and simulation results show that selecting the appropriate power and modulation orders can improve the throughput by about 3 dB at high SNRs. The impact of the SNR quantization is evaluated, and the obtained results show that the proposed system can tolerate large quantization steps, which enables reducing the complexity of the optimization and adaptation processes.

Path Design and Resource Management for NOMA Enhanced Indoor Intelligent Robots

A communication enabled indoor intelligent robots (IRs) service framework is proposed, where non-orthogonal multiple access (NOMA) technique is adopted to enable highly reliable communications. In cooperation with the ultramodern indoor channel model recently proposed by the International Telecommunication Union (ITU), the Lego modeling method is proposed, which can deterministically describe the indoor layout and channel state in order to construct the radio map. The investigated radio map is invoked as a virtual environment to train the reinforcement learning agent, which can save training time and hardware costs. Build on the proposed communication model, motions of IRs who need to reach designated mission destinations and their corresponding down-link power allocation policy are jointly optimized to maximize the mission efficiency and communication reliability of IRs. In an effort to solve this optimization problem, a novel reinforcement learning approach named deep transfer deterministic policy gradient (DT-DPG) algorithm is proposed. Our simulation results demonstrate in the following: 1) with the aid of NOMA techniques, the communication reliability of IRs is effectively improved; 2) radio map is qualified to be a virtual training environment, and its statistical channel state information improves training efficiency by about 30%; 3) proposed DT-DPG algorithm is superior to the conventional deep deterministic policy gradient (DDPG) algorithm in terms of optimization performance, training time, and anti-local optimum ability.

Beyond Nonorthogonal Multiple Access: New Role of Constructive Interference

In this letter, we introduce a novel framework of constructive non-orthogonal multiple access (NOMA) transmission, which provides the merit of interference utilization and breaks through the constructive interference (CI)’s limitation on multiuser (MU) access capability. With dedicated synthetic successive coding and hybrid MU access designs, a novel constructive NOMA (CNOMA) precoder is proposed, which is particularly suitable for the scenario where users have heterogeneous throughput requirements. Explicitly, it makes the composite interference always beneficial to the users having high throughput requirement, while accommodating another sets of users under their subscribed reception-quality requirement. Finally, a number of fundamental properties of the CNOMA design is revealed, such as the tradeoff between utilization of MU interference and improvement of MU access capability. Simulation demonstrates that the proposed CNOMA precoder significantly outperforms the classic CI and minimum-mean-square-error precoders in throughput performance, and meanwhile obtains high access capability close to classic NOMA designs.

Robust transmit beamforming design for multi‐cell multiuser MIMO NOMA

This paper focuses on the robust beamforming design for downlink multi-cell multiple-input multiple-output (MIMO) nonorthogonal multiple access (NOMA) systems without having any restrictions on the number of users and cells. The beamforming matrices are designed by solving a sum rate maximization problem under imperfect channel state information (CSI) while satisfying transmission power constraints. In order to solve the proposed non-convex optimization problem with infinite-dimensional robust constraints, an iterative algorithm is provided to transform this problem into a convex form by utilizing diagonalization theory and introducing some auxiliary variables. Numerical results demonstrate that the proposed algorithm converges quickly, and the proposed robust NOMA design achieves strong robustness and acceptable performance.

NOMA Beamforming in SDMA Networks: Riding on Existing Beams or Forming New Ones?

In this letter, the design of non-orthogonal multiple access (NOMA) beamforming is investigated in a spatial division multiple access (SDMA) legacy system. In particular, two popular beamforming strategies in the NOMA literature, one to use existing SDMA beams and the other to form new beams, are adopted and compared. The studies carried out in the letter show that the two strategies realize different tradeoffs between system performance and complexity. For example, riding on existing beams offers a significant reduction in computational complexity, at the price of a slight performance loss. Furthermore, this simple strategy can realize the optimal performance when the users’ channels are structured.

On the Energy Efficiency Maximization of NOMA-Aided Downlink Networks With Dynamic User Pairing

This study investigates a combined system comprising non-orthogonal multiple access (NOMA) and beamforming in a downlink network. To fully exploit the advantages of NOMA, user (UE) pairing and beamforming design are jointly optimized via a generalized model for UE association, subject to energy efficiency maximization. Owing to the combination of binary variables and nonconvex constraints, the resulting optimization problem belongs to the class of mixed-integer nonconvex programming. An innovative algorithm, integrating the inner-approximation and Dinkelbach methods, is proposed herein to address a nonconvex fractional function. By introducing a pairing matrix and relaxing the binary variables into continuous ones, our approach is capable of reaching an optimal solution, where two arbitrary UEs are optimally paired regardless of geographical or spatial constraints. For practical scenarios, we further propose a robust design to manage the effect of channel estimation errors under settings involving channel uncertainty. Numerical results show that our proposed designs, even with the presence of the imperfect channel state information at the base station, significantly outperform the conventional beamforming and existing pairing schemes.

Sum Secrecy Rate Maximization in NOMA-Based Cognitive Satellite-Terrestrial Network

In this letter, we present a joint beamforming design for non-orthogonal multiple access (NOMA)-based cognitive satellite-terrestrial network (CSTN), where satellite network applies orthogonal multiple access (OMA) technology and NOMA scheme is utilized by the terrestrial network. The scheme key is to maximize sum secrecy rate of satellite users under the imperfect channel state information, while meeting the rate requirements of terrestrial users and transmit power constraints of the CSTN. Since the formulated optimization problem is non convex and intractable, we convert the original non convex maximization problem to a corresponding tractable convex one by successive convex approximation (SCA) and semidefinite relaxation (SDR), and then propose an SCA-based iterative beamforming algorithm to get the secure beamforming vectors. Finally, numerical simulation results are provided to verify the effectiveness and superiority of the proposed joint beamforming design.

Max-Min Fair Precoder Design and Power Allocation for MU-MIMO NOMA

In this correspondence, transmit precoders and their power allocation coefficients are designed jointly for a downlink non-orthogonal multiple access (NOMA) wireless communication system. The objective is to provide max-min fairness (MMF) among the strongest users in each group, while maintaining minimum target rates for all the other users. The proposed solutions are respectively based on semi-definite relaxation (SDR) and successive convex approximation (SCA) and on the minimum mean square error (MMSE) approaches. For the latter approach, a simplification is also suggested to lower complexity. It is shown that while rate-splitting (RS) has the best MMF rates, the low-complexity MMSE approach has the least complexity. Moreover, the SDR/SCA approach offers an excellent tradeoff between the two.

Asynchronous Transmission for Multiple Access Channels: Rate-Region Analysis and System Design for Uplink NOMA

In this work, we thoroughly analyze the rate-region provided by the asynchronous transmission in multiple access channels (MACs). We derive the corresponding capacity-regions, applicable to a wide range of pulse shaping methods. We analytically prove that asynchronous transmission enlarges the capacity-region of MACs. Although successive interference cancellation (SIC) can achieve the optimal sum-rate for the conventional uplink non-orthogonal multiple access (NOMA) methods, it is unable to achieve the boundary of the capacity-region for the asynchronous transmission. We demonstrate that for the asynchronous transmission, the optimal SIC decoding order to achieve the maximum sum-rate is based on the users' channel strengths. This optimal ordering is in contrast to the conventional uplink NOMA, where various decoding orders can result in the maximum sum-rate. Furthermore, we provide practical transceiver designs to approach the capacity-region. The memory induced by asynchronous transmission enables the use of the trellis-based detection methods which improves the performance. In addition, we propose a transceiver design, based on channel diagonalization to exploit the frequency-selectivity introduced by timing offsets. The proposed transceiver design, joint with the turbo principle, enables us to achieve a rate pair that is not achievable by the synchronous transmission.

A Minimum Error Probability NOMA Design

Non-orthogonal multiple access (NOMA) enables massive connectivity and achieves high spectral efficiency. The vast majority of the NOMA literature has adopted the ideal information rate as performance metric assuming perfect successive interference cancellation (SIC) without any error propagation, which, however, may lead to NOMA designs adverse to SIC. In this paper, we take into account imperfect SIC and practical modulation schemes for power-domain NOMA design. To characterize the error propagation, we derive the bit error rates (BERs) of the users for arbitrary-order quadrature amplitude modulation (QAM) schemes. Then, we propose a minimum error probability NOMA (MEP-NOMA) design, minimizing the average BER of the users via power allocation. Considering the complicated error probability expressions of the MEP-NOMA design, we derive lower and upper bounds on the average BER, based on which a simple closed-form power allocation is obtained. We show that the proposed power allocation minimizes both the lower and upper bounds on the average BER for a sufficiently large power budget and provides near-optimal error performance. On this basis, we theoretically prove the superiority of MEP-NOMA over existing OMA and NOMA schemes in terms of error performance. Comprehensive numerical results are provided to verify the accuracy of the error probability analysis of the considered practical NOMA scheme with imperfect SIC and to demonstrate the efficacy of the proposed MEP-NOMA design.

A Framework of Uplink-Downlink NOMA Protocol for Multiple Access in IoT-Oriented Networks

With the fast development of wireless systems and internet of things (IoT), non-orthogonal multiple access (NOMA) has been studied as one of effective schemes to meet increasing demands of massive users. Two types of NOMA transmission, i.e., uplink (UL) and downlink (DL), have been explored in term of mathematical analysis. The first one is derivation of outage probability for UL, DL. The second, we find parameters to adjust system performance to meet requirement in design of NOMA in practice.

Rate Fairness and Power Consumption Optimization for NOMA-Assisted Downlink Networks

This paper considers a non-orthogonal multiple access (NOMA) downlink network, where a hybrid of NOMA and beamforming designs is developed to enhance the channel capacity. We aim to improve the system performance in terms of rate fairness and power consumption. Hence, a multi-objective problem with a joint optimization of user equipment pairing, power control, and quality-of-service requirements is addressed. To efficiently solve the problem, we propose two low-complexity algorithms based on the inner-approximation method, with the first algorithm using the relaxation method and the second one using graph theory. Numerical results are provided to demonstrate the effectiveness of the two proposed algorithms in comparison with the exhaustive search and existing methods.