Non-orthogonal Multiple Access In Terms Research Articles

Resource Allocation in UAV-Enabled NOMA Networks for Enhanced Six-G Communications Systems

Enhancing energy efficiency, content distribution, latency, and transmission speeds are vital components of communication systems. Multiple access methods hold great promise for boosting these performance indicators. This manuscript evaluates the effectiveness of Non-Orthogonal Multiple Access (NOMA) and Orthogonal Multiple Access (OMA) systems within a single cell, where users are scattered randomly and rely on relays for dependability. This paper presents a model for improving energy efficiency, content distribution, latency, and transmission speeds in communication systems using NOMA and OMA systems within a single cell. Additionally, this paper also proposes a caching strategy using unmanned aerial vehicles (UAVs) as aerial base stations for ground users. These UAVs distribute cached content to minimize the overall latency of content demands from ground users while modifying their positions. We carried out simulations using various cache capacities and user counts linked to their respective UAVs. Furthermore, we evaluated OMA and NOMA in terms of the achievable rate and energy efficiency. The proposed model has achieved noteworthy enhancement across various scenarios including different sum rates, numbers of mobility users, diverse cache sizes, and amounts of power allocation.

Ambient BackCom in beyond 5G NOMA networks: A multi-cell resource allocation framework

The research of Non-Orthogonal Multiple Access (NOMA) is extensively used to improve the capacity of networks beyond the fifth-generation. The recent merger of NOMA with ambient Backscatter Communication (BackCom), though opening new possibilities for massive connectivity, poses several challenges in dense wireless networks. One such challenge is the performance degradation of ambient BackCom in multi-cell NOMA networks under the effect of inter-cell interference. Driven by providing an efficient solution to the issue, this article proposes a new resource allocation framework that uses a duality theory approach. Specifically, the sum rate of the multi-cell network with backscatter tags and NOMA user equipment is maximized by formulating a joint optimization problem. To find the efficient base station transmit power and backscatter reflection coefficient in each cell, the original problem is first divided into two subproblems, and then the closed form solution is derived. A comparison with the Orthogonal Multiple Access (OMA) ambient BackCom and pure NOMA transmission has been provided. Simulation results of the proposed NOMA ambient BackCom indicate a significant improvement over the OMA ambient BackCom and pure NOMA in terms of sum-rate gains.

Modeling and Simulating NOMA Performance for Next Generations

Non-orthogonal multiple access (NOMA) is a multiple access technique that allows multiple users to share the same communication resources, resulting in increased spectral efficiency and throughput. NOMA has been shown to provide significant performance gains over orthogonal multiple access (OMA) in terms of spectral efficiency and throughput. In this paper, two scenarios of NOMA are analyzed and simulated, involving two users and multiple users (four users) in order to evaluate the performance of NOMA in terms of bits per error ratio (BER) and achievable sum-rate (R-sum), then comparing NOMA with OMA in terms of achievable sum rate. The obtained results indicate that an improvement is achieved for two users NOMA (16.7 (bps/Hz)) compared with OMA (15.53(bps/Hz)), while for multi-users NOMA (20.69 (bps/Hz)) compared with OMA (15.79 (bps/Hz)) at transmitted power equal to 25 dBm.

Rate-Splitting Multiple Access for Multi-Antenna Downlink Communication Systems: Spectral and Energy Efficiency Tradeoff

Rate-splitting (RS) has recently been recognized as a promising physical-layer technique for multi-antenna broadcast channels (BC). Due to its ability to partially decode the interference and partially treat the remaining interference as noise, RS is an enabler for a powerful multiple access, namely rate-splitting multiple access (RSMA), that has been shown to achieve higher spectral efficiency (SE) and energy efficiency (EE) than both space division multiple access (SDMA) and non-orthogonal multiple access (NOMA) in a wide range of user deployments and network loads. As SE maximization and EE maximization are two conflicting objectives in the moderate and high signal-to-noise ratio (SNR) regimes, the study of the tradeoff between the two criteria is of particular interest. In this work, we address the SE-EE tradeoff by studying the joint SE and EE maximization problem of RSMA in multiple input single output (MISO) BC with rate-dependent circuit power consumption at the transmitter. To tackle the challenges coming from multiple objective functions and rate-dependent circuit power consumption, we first propose two models to transform the original problem into two single-objective problems, namely, weighted-sum method and weighted-power method. A low-complexity algorithm with closed-form solution is proposed to solve each single-objective problem in the two-user system. For the generalized <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> -user system, a successive convex approximation (SCA)-based algorithm is then proposed to optimize the precoders of each transformed problem. Numerical results show that our algorithm converges much faster than existing algorithms. In addition, the performance of RSMA is superior to or equal to SDMA and NOMA in terms of SE, EE and their tradeoff.

On the Performance of Cooperative Relaying Systems with NOMA in κ − μ Fading Environment

Nonorthogonal multiple access (NOMA) is considered to be a promising solution for the fifth generation (5G) wireless networks. The performance of the 5G wireless networks in terms of outage probability, achievable rate, and other important network performance metrics can be remarkably improved by the integration of NOMA with cooperative relaying transmission technique. In this paper, we investigate the performance of the cooperative relaying system integrated with NOMA in terms of outage probability and achievable rate over κ − μ fading channels. Analytical expressions for the outage probability and the achievable rate are obtained for the system mentioned above. Moreover, corresponding expressions for Rician and Rayleigh fading channels are also presented in this paper as special cases of κ − μ fading channels. Some numerical examples are presented here for illustration purposes. The analytical results obtained in this paper are all validated via simulation.

Sum Rate Maximization-based Fair Power Allocation in Downlink NOMA Networks

Non-orthogonal multiple access (NOMA) has been seen as a promising technology for 5G communication. The performance optimization of NOMA systems depends on both power allocation (PA) and user pairing (UP). Most existing researches provide sub-optimal solutions with high computational complexity for PA problem and mainly focuses on maximizing the sum rate (capacity) without considering the fairness performance. Also, the joint optimization of PA and UP needs an exhaustive search. The main contribution of this paper is the proposing of a novel capacity maximization-based fair power allocation (CMFPA) with low-complexity in downlink NOMA. Extensive investigation and analysis of the joint impact of signal to noise ratio (SNR) per subcarrier and the channel gains of the paired users on the performance of NOMA in terms of the capacity and the user fairness is presented. Next, a closed-form equation for the power allocation coefficient of CMFPA as a function of SNR, and the channel gains of the paired users is provided. In addition, to jointly optimize UP and PA in NOMA systems an efficient low-complexity UP (ELCUP) method is proposed to be incorporated with the proposed CMFPA to compromise the proposed joint resource allocation (JRA). Simulation results demonstrate that the proposed CMFPA can improve the capacity and fairness performance of existing UP methods, such as conventional UP, and random UP methods. Furthermore, the simulation results show that the proposed JRA significantly outperforms the existing schemes and gives a near-optimal performance.

Performance of downlink NOMA‐enabled vehicular communications over double Rayleigh fading channels

Non-orthogonal multiple access (NOMA) is an attractive candidate for future wireless networks. Recently, vehicular communications with NOMA have received substantial research attention owing to their appealing advantages. In this study, the authors investigate the performance of downlink power-domain NOMA-enabled vehicular communications, in which a base station communicates with two users UE1 (far user) and UE2 (near user). Since all the nodes are moving vehicles, the channels for vehicular links experience independent and non-identically distributed double-Rayleigh fading. Specifically, the authors derive the outage probabilities of individual users and overall system under two scenarios of interest, viz. (i) when the rate of NOMA system falls below the fixed target rate and (ii) when NOMA system achieves lower rate than orthogonal multiple access (OMA) rate. The authors also derive the average bit error rate (ABER) and ergodic capacity expressions for the considered system. The numerical and simulation results validate the proposed analytical findings, and demonstrate the impacts of various parameters on the system performance. The authors further show that NOMA scheme is superior than OMA in terms of outage probability and ergodic capacity, whereas OMA outperforms NOMA in terms of ABER because OMA users do not have inter-user interferences.

A Survey on Non-Orthogonal Multiple Access: From the Perspective of Spectral Efficiency and Energy Efficiency

Non-orthogonal multiple access (NOMA) is a promising technology for next-generation wireless networks with emerging demands on low latency, high throughput, and massive connectivity. Unlike orthogonal multiple access, NOMA allows multiple users to share the same radio resources, which significantly improves spectral efficiency (SE). To achieve green wireless communications for numerous networked devices, NOMA helps reduce energy consumption while satisfying rate fairness and quality-of-experience requirements. The goal of this paper is to introduce the innovative approaches for NOMA in terms of the SE and energy efficiency, and discuss emerging technologies involved with NOMA. Further, its challenges and future research directions are highlighted.

An Analysis of Two-User Uplink Asynchronous Non-orthogonal Multiple Access Systems

Recent studies have numerically demonstrated the possible advantages of the asynchronous non-orthogonal multiple access (ANOMA) over the conventional synchronous non-orthogonal multiple access (NOMA). The ANOMA makes use of the oversampling technique by intentionally introducing a timing mismatch between symbols of different users. Focusing on a two-user uplink system, for the first time, we analytically prove that the ANOMA with a sufficiently large frame length can always outperform the NOMA in terms of the sum throughput. To this end, we derive the expression for the sum throughput of the ANOMA as a function of signal-to-noise ratio (SNR), frame length, and normalized timing mismatch. Based on the derived expression, we find that users should transmit at full powers to maximize the sum throughput. In addition, we obtain the optimal timing mismatch as the frame length goes to infinity. Moreover, we comprehensively study the impact of timing error on the ANOMA throughput performance. Two types of timing error, i.e., the synchronization timing error and the coordination timing error, are considered. We derive the throughput loss incurred by both types of timing error and find that the synchronization timing error has a greater impact on the throughput performance compared to the coordination timing error.

Exploiting Full/Half-Duplex User Relaying in NOMA Systems

In this paper, a novel cooperative non-orthogonal multiple access (NOMA) system is proposed, where one near user is employed as decode-and-forward (DF) relaying switching between full-duplex (FD) and half-duplex (HD) mode to help a far user. Two representative cooperative relaying scenarios are investigated insightfully. The \emph{first scenario} is that no direct link exists between the base station (BS) and far user. The \emph{second scenario} is that the direct link exists between the BS and far user. To characterize the performance of potential gains brought by FD NOMA in two considered scenarios, three performance metrics outage probability, ergodic rate and energy efficiency are discussed. More particularly, we derive new closed-form expressions for both exact and asymptotic outage probabilities as well as delay-limited throughput for two NOMA users. Based on the derived results, the diversity orders achieved by users are obtained. We confirm that the use of direct link overcomes zero diversity order of far NOMA user inherent to FD relaying. Additionally, we derive new closed-form expressions for asymptotic ergodic rates. Based on these, the high signal-to-noise radio (SNR) slopes of two users for FD NOMA are obtained. Simulation results demonstrate that: 1) FD NOMA is superior to HD NOMA in terms of outage probability and ergodic sum rate in the low SNR region; and 2) In delay-limited transmission mode, FD NOMA has higher energy efficiency than HD NOMA in the low SNR region; However, in delay-tolerant transmission mode, the system energy efficiency of HD NOMA exceeds FD NOMA in the high SNR region.

Performance Analysis of User Pairing in Cooperative NOMA Networks

In this paper, we study the coverage probability and average data rate of user pairing in cooperative non-orthogonal multiple access (NOMA) networks. With fixed locations of the source and typical user, the candidate users for pairing follow homogeneous Poisson point process. Considering the geometric distance between nodes, close-to-user pairing (CUP) and close-to-source pairing (CSP) schemes are investigated with the near user acting as half-duplex relay or full-duplex (FD) relay. Lower bounds on the coverage probability and average data rate are approximately obtained using stochastic geometry and Gaussian–Chebyshev quadrature. Numerical and simulation results corroborate the accuracy of the analytical results and reveal that CUP-based cooperative NOMA outperforms CSP-based cooperative NOMA in terms of the data rate performance. With typical user close to the source, CUP-based FD NOMA is the best transmission scheme (among CUP-based and CSP-based cooperative NOMA, non-cooperative NOMA, and OMA schemes) that maximizes the sum data rate and the minimum user rate.

Resource Allocation in Non-Orthogonal and Hybrid Multiple Access System With Proportional Rate Constraint

Non-orthogonal multiple access (NOMA), which has attracted a lot of attention recently due to its superior spectral efficiency, could play a vital role in improving the capacity of future networks. In this paper, a resource allocation scheme is developed for a downlink multi-user NOMA system. An optimization problem is formulated to maximize the sum rate under the total power and proportional rate constraints. Due to the complexity of computing the optimal solution, we develop a low complexity sub-optimal solution for a two-user scenario and then extend it to the multi-user case by proposing a user-pairing approach as well as a number of power allocation techniques that facilitate dealing with a large number of users in NOMA system. Simulation results support the effectiveness of the proposed approaches and show the close performance to the optimal one. In addition, we propose a new hybrid multiple access technique that combines the properties of NOMA and the orthogonal frequency division multiple access. Simulation results show that the proposed hybrid method provides better performance than NOMA in terms of the overall achievable sum rate and the coverage probability.

Rate region analysis in a full-duplex-aided cooperative nonorthogonal multiple-access system

Nonorthogonal multiple access (NOMA) with successive interference cancellation is considered as one of the most promising schemes in multi-user access wireless networks. Based on the principles of NOMA and full-duplex (FD) communications, this paper proposes a novel FD-aided cooperative NOMA (FD-NOMA) scheme to optimize the maximum achievable rate region. Since self-interference often exists in FD communications, a self-interference canceller is employed in this system. Specifically, three schemes that aim to maximize the achievable rate region are provided. The first one is investigated under the assumption that the transmitted power is fixed, while the other two schemes are achieved with the aid of two developed algorithms. For the purpose of studying the rate region in the non-ideality condition, the error vector magnitudelevel is introduced in the analysis of the third scheme. Finally, analytical results demonstrate that the proposed FD-NOMA scheme outperforms the conventional schemes based on NOMA in terms of the rate region, and the maximum rate region of the FD-NOMA scheme is compared with different coefficients.