Outage Performance of Non-Orthogonal Multiple Access Based Unmanned Aerial Vehicles Satellite Networks

With rapid development of unmanned aerial vehicles(UAVs), more and more UAVs access satellite networks for data transmission. To improve the spectral efficiency, non-orthogonal multiple access(NOMA) is adopted to integrate UAVs into the satellite network, where multiple satellites cooperatively serve the UAVs and mobile terminal using the Ku-band and above. Taking into account the rain fading and the fading correlation, the outage performance is first analytically obtained for fixed power allocation and then efficiently calculated by the proposed power allocation algorithm to guarantee the user fairness. Simulation results verify the outage performance analysis and show the performance improvement of the proposed power allocation scheme.

Non-Orthogonal Multiple Access in Cell-Free Massive MIMO Networks

In this paper, we investigate the downlink performance of cell-free massive multi-input multi-output non-orthogonal multiple access(CF-m MIMO-NOMA) system with conjugate beamforming precoder and compare against the orthogonal multiple access(OMA) counterpart. A novel achievable closed-form spectral efficiency(SE) expression is derived, which characterizes the effects of the channel estimation error, pilot contamination, imperfect successive interference cancellation(SIC) operation, and power optimization technique. Then, motivated by the closedform result, a sum-SE maximization algorithm with the sequential convex approximation(SCA) is proposed, subject to each AP power constraint and SIC power constraint. Numerical experiments indicate that the proposed sum-SE maximization algorithms have a fast converge rate, within about five iterations. In addition, compared with the full power control(FPC) scheme, our algorithms can significantly improve the achievable sum-SE. Moreover, NOMA outperforms OMA in many respects in the presence of the proposed algorithms.

Frameworks of Non-Orthogonal Multiple Access Techniques in Cognitive Radio Communication Systems

Recently,the increasing demand of radio spectrum for the next generation communication systems due to the explosive growth of applications appetite for bandwidths has led to the problem of spectrum scarcity.The potential approaches among the proposed solutions to resolve this issue are well explored cognitive radio(CR)technology and recently introduced non-orthogonal multiple access(NOMA)techniques.Both the techniques are employed for efficient spectrum utilization and assure the significant improvement in the spectral efficiency.Further,the significant improvement in spectral efficiency can be achieved by combining both the techniques.Since the CR is well-explored technique as compared to that of the NOMA in the field of communication,therefore it is worth and wise to implement this technique over the CR.In this article,we have presented the frameworks of NOMA implementation over CR as well as the feasibility of proposed frameworks.Further,the differences between proposed CR-NOMA and conventional CR frameworks are discussed.Finally,the potential issues regarding the implementation of CR-NOMA are explored.

Resource Allocation Based on User Pairing and Subcarrier Matching for Downlink Non-Orthogonal Multiple Access Networks

The traditional orthogonal multiple access(OMA)is unable to satisfy the needs of large number of smart devices.To increase the transmission rate in the limited spectrum resource,implementation of both non-orthogonal multiple access(NOMA)and successive interference cancelation(SIC)is essential.In this paper,an optimal resource allocation algorithm in NOMA is proposed to maximize the total system rate in a multi-sector multi-subcarrier relay-assisted communication network.Since the original problem is a non-convex problem with mixed integer programming which is non-deterministic polynomial-time(NP)-hard,a three-step solution is proposed to solve the primal problem.Firstly,we determine the optimal power allocation of the outer users by using the approach of monotonic discrimination,and then the optimal user pairing is determined.Secondly,the successive convex approximation(SCA)method is introduced to transform the non-convex problem involving central users into convex one,and the Lagrangian dual method is used to determine the optimal solution.Finally,the standard Hungarian algorithm is utilized to determine the optimal subcarrier matching.The simulation results show that resource allocation algorithm is able to meet the user performance requirements with NOMA,and the total system rate is improved compared to the existing algorithms.

Joint Non-Orthogonal Multiple Access (NOMA) & Walsh-Hadamard Transform: Enhancing the Receiver Performance

Non-orthogonal multiple access(NOMA) is a new access method to achieve high performance gains in terms of capacity and throughput, so it is currently under consideration as one of the candidates for fifth generation(5 G) technologies. NOMA utilizes power domain in order to superimpose signals of multiple users in a single transmitted signal. This creates a lot of interference at the receive side. Although the use of successive interference cancellation(SIC) technique reduces the interference, but to further improve the receiver performance, in this paper, we have proposed a joint Walsh-Hadamard transform(WHT) and NOMA approach for achieving better performance gains than the conventional NOMA. WHT is a well-known code used in communication systems and is used as an orthogonal variable spreading factor(OVSF) in communication systems. Application of WHT to NOMA results in low bit error rate(BER) and high throughput performance for both low and high channel gain users. Further, it also reduces peak to average power ratio(PAPR) of the user signal. The results are discussed in terms of comparison between the conventionalNOMA and the proposed technique, which shows that it offers high performance gains in terms of low BER at different SNR levels, reduced PAPR, high user throughput performance and better spectral efficiency.

Exploiting Spectral-Energy Efficiency Tradeoff with Fairness in Non-Orthogonal Multiple Access Systems

The spectral efficiency(SE)and energy efficiency(EE)tradeoff while ensuring rate fairness among users in non-orthogonal multiple access(NOMA)systems is investigated.In order to characterize the SE-EE tradeoff with rate fairness,a multi-objective optimization(MOO)problem is first formulated,where the rate fairness is represented with theα-fair utility function.Then,the MOO problem is converted into a single-objective optimization(SOO)problem by the weighted sum method.To solve the converted non-convex SOO problem,we apply sequential convex programming,which helps to propose a general power allocation algorithm to realize the SE-EE tradeoff with rate fairness.We prove the convergence of the proposed algorithm and the convergent solution satisfies the KKT conditions.Simulation results demonstrate the proposed power allocation algorithm can achieve various levels of rate fairness,and higher fairness results in degraded performance of SE-EE tradeoff.A pivotal conclusion is reached that NOMA systems significantly outperform orthogonal multiple access systems in terms of SE-EE tradeoff with the same level of rate fairness.

An Overview of Non.Orthogonal Multiple Access

In recent years, non-orthogonal multiple access(NOMA) has attracted a lot of attention as a novel and promising power-domain us-er multiplexing scheme for Long-Term Evolution(LTE) enhancement and 5G. NOMA is able to contribute to the improvement ofthe tradeoff between system capacity and user fairness(i.e., cell-edge user experience). This improvement becomes in particularemphasized in a cellular system where the channel conditions vary significantly among users due to the near-far effect. In this arti-cle, we provide an overview of the concept, design and performance of NOMA. In addition, we review the potential benefits and is-sues of NOMA over orthogonal multiple access(OMA) such as orthogonal frequency division multiple access(OFDMA) adoptedby LTE, and the status of 3GPP standardization related to NOMA.

基于PD-NOMA的人员监控图像传输算法

危险区域人员监控具有摄像节点密度高、传输实时性和图像质量要求高的特点。功率域非正交多址接入(PD-NOMA)技术可以支持多路并行传输,有利于在密集传输场景下提升传输实时性,而多摄像节点协同有利于提高图像质量。在面向危险区域人员监控的PD-NOMA摄像网络中,提出通过多图融合的人员监控图像传输算法,以实现高质量监控。首先,定义了图像的“单人信息量”这一关键术语,它反映了图像中单个人员被准确识别的概率;其次,基于摄像节点之间的位置关系定义了多摄像节点拍摄到的单个人员的融合图像信息量;最后,在满足传输实时性要求以及图像中所有人员均可识别的前提下,以最大化融合图像信息量为目标,计算以摄像节点的图像分辨率和无线发射功率为控制变量的实时传输调度方案。实验结果表明,当实时传输上限为0.4 s时,基于PD-NOMA的传输调度方案传输信息量比传统传输方案提高了46.4%,使得图像中人员识别概率从0.8549提升至0.8919。

Enhanced uplink non-orthogonal multiple access for 5G and beyond systems

Uplink non-orthogonM multiple access （NOMA） is a promising technique to meet the requirements of the fifth generation （5G） and beyond systems. Various NOMA schemes have been proposed in both academia and industry. However, most existing schemes assume equal average received power, which limits the performance. We propose three enhancements of uplink NOMA to achieve the requirements of massive connectivity and high reliability in 5G, where unequal average received power is exploited as part of the multiple access signature. First, the optimal sequences targeting to generalized Welch-bound equality （GWBE） are obtained for unequal average received power. Then user grouping with multi-level received powers is proposed for better successive interference cancellation （SIC） at the receiver. Finally, sequence grouping based on the cross-correlation properties of sequences is proposed to reduce inter-and intra-group interference. Simulation results show that by incorporating multi-level received powers and sequence grouping into existing NOMA schemes, for an NOMA system with 400% overloading and fixed signature allocation, 3 dB and 10 dB signal-to-noise ratio （SNR） gains at 0.1 block error rate （BLER） target can be achieved compared with existing NOMA schemes and orthogonal multiple access （OMA）, respectively. Besides, 0.01 BLER target can be achieved while an error floor exists in existing NOMA schemes. Under random sequence selection, collision probability is reduced by multi-level powers. In addition, GWBE sequences achieve lower BLER than existing sequences and the gain is large especially for low BLER requirements. This shows that the proposed scheme can support larger connectivity and higher reliability.

Sensing-Communication-Computing-Control Closed Loop for NOMA-UAV Systems

In the areas without terrestrial communication infrastructures,unmanned aerial vehicles(UAVs)can be utilized to serve field robots for mission-critical tasks.For this purpose,UAVs can be equipped with sensing,communication,and computing modules to support various requirements of robots.In the task process,different modules assist the robots to perform tasks in a closed-loop way,which is referred to as a sensing-communication-computing-control(SC3)loop.In this work,we investigate a UAV-aided system containing multiple SC^(3)loops,which leverages non-orthogonal multiple access(NOMA)for efficient resource sharing.We describe and compare three different modelling levels for the SC^(3)loop.Based on the entropy SC^(3)loop model,a sum linear quadratic regulator(LQR)control cost minimization problem is formulated by optimizing the communication power.Further for the assure-to-be-stable case,we show that the original problem can be approximated by a modified user fairness problem,and accordingly gain more insights into the optimal solutions.Simulation results demonstrate the performance gain of using NOMA in such task-oriented systems,as well as the superiority of our proposed closed-loop-oriented design.

A Near Optimal Power Allocation Scheme for Cooperative Relay Networking with NOMA

In this paper, we propose cooperative relay networks with non-orthogonal multiple access in order to design a near-optimal power allocation strategy. Like other next generation wireless technologies, spatially multiplexed transmissions are achieved by relay nodes which enables decode-and-forward relaying of a new superposition code after reception from the source. It is worth noting that, since it is hard to exactly prove the proposed PA scheme, due the fact that it is one kind of the approximate conjectures. Therefore, mathematical and numerical methods have been used to clarify the feasibility of the proposal. Numerical results indicate that it is able to asymptotically achieve the optimal sum rate at the higher signal-to-noise ratio region with the proposed strategy applied instead of negligible performance loss.

Random Access and Resource Allocation for the Coexistence of NOMA-Based and OMA-Based M2M Communications

In the future fifth generation(5G) systems,non-orthogonal multiple access(NOMA) is a promising technology that can greatly enhance the network capacity compared to orthogonal multiple access(OMA) .In this paper,we propose a novel random access(RA) and resource allocation scheme for the coexistence of NOMA-based and OMAbased machine-to-machine(M2M) communications,which aims at improving the number of successful data packet transmissions and guaranteeing the quality of service(Qo S) (e.g.,the minimum data rate requirement) for M2 M communications.The algorithm of joint user equipment(UE) paring and power allocation is proposed for the coexisting RA(i.e.,the coexistence of NOMA-based RA and OMA-based RA) .The resource allocation for the coexisting RA is investigated,thus improving the number of successful data packet transmissions by more efficiently using the radio resources.Simulation results demonstrate that the proposed RA and resource allocation scheme outperforms the conventional RA in terms of the number of successful data packet transmissions,thus is a promising technology in future M2 M communications.

实时工业物联网的功率域非正交多址接入基站选址算法

针对工业物联网(IoT)中接入延迟较大的问题,提出一种实时工业IoT的功率域非正交多址接入(PDNOMA)基站选址算法。该算法在PD-NOMA技术的基础上,以数据收集基站的位置为优化手段,通过最大限度地实现用户功率分复用来实现接入延迟的最小化。首先,证明对任意两用户若实现它们的并行传输,则合格的基站可解码区域必为圆,因此,所有的两用户组合可得到基站可解码区域的集合,且集合中区域间的每个最小相交区域必为凸区域,从而可知这些最小相交区域必定包含数据收集基站的最优位置。然后,对于每一个最小相交区域,以基站放置在该区域的网络生成图的最小链划分数作为接入延迟的度量标准。最后,通过最小链划分数的比较得出基站的最优位置。实验结果表明,解码阈值为2用户数为30时,所提算法的平均接入延迟降低为经典时分多路方式的36.7%,并且随着解码阈值的降低和信道衰减因子的增加,接入延迟可获得近似线性的降低。所提算法对海量超可靠低延迟通信从接入层角度提供了参考。

Research on User Pairing Techniques Based on NOMA in Cognitive Radio Networks

This paper outlined a Non-Orthogonal Multiple Access (NOMA) grouping transmission scheme for cognitive radio networks. To address the problems of small channel gain difference of the middle part users caused by the traditional far-near pairing algorithm, and the low transmission rate of the traditional Orthogonal Multiple Access (OMA) transmission, a joint pairing algorithm was proposed, which provided multiple pairing schemes according to the actual scene. Firstly, the secondary users were sorted according to their channel gain, and then different secondary user groups were divided, and the far-near pairing combined with (Uniform Channel Gain Difference (UCGD) algorithm was used to group the secondary users. After completing the user pairing, the power allocation problem was solved. Finally, the simulation data results showed that the proposed algorithm can effectively improve the system transmission rate.

无线网络中的功率域非正交多址接入技术

功率域非正交多址接入(Dower Domain Non-orthogonal Multiple Access,PD-NOMA)技术,作为未来无线通信系统中重要的多址接入技术之一,可满足系统高频谱效率、高连接密度及低时延等需求。相比正交多址接入技术(Orthogonal Multiple,OMA),PD-NOMA利用用户间信道差异、功率域复用及串行干扰消除算法,实现多用户同时共享时、频、码资源。为推动功率域非正交多址接入技术的学术研究与实际应用,梳理了其基本原理,并从信息论角度验证了其相比正交多址接入技术可获得更高的频谱效率。基于PD-NOMA的现存研究工作,分别归纳讨论了单天线PD-NOMA、多天线PD-NOMA、协作PD-NOMA、能效PD-NOMA、可见光通信中的PD-NOMA、认知PD-NOMA及PD-NOMA的性能优化等关键技术研究方向。针对上述方向,进一步剖析了其未来研究趋势,并分别从接收机设计、信令开销、物联网应用及标准化4个方面深入探讨PD-NOMA在实际应用中所面临的难题。最后指出PD-NOMA的基本理论研究已接近成熟,但多技术融合仍需深入研究以加快该技术成果转化,从而充分发挥其在未来无线网络中的高频谱效率优势。

5G非正交多址技术关键问题研究

非正交多址接入(NOMA)技术是5G通信的关键技术之一。该技术采用功率域复用的方式增加用户接入数,具有较高的频谱效率和可靠性,应用前景广泛。因此,研究5G非正交多址接入技术具有相当重要的意义。尤其是对其关键问题,如用户间的资源分配和多址干扰的消除等方面的问题,更值得深入研究。分别对这两个关键问题,就国内外目前的研究进展进行了详尽的分析和探讨。从实际多用户小区的资源分配、单一的串行干扰消除技术出发,总结了目前研究中所存在的问题,并提出相关解决方案,为更好地发挥NOMA技术的性能优势、抑制多用户共享资源带来的多址干扰问题提供参考。随着研究的深入,资源分配和干扰消除两大关键问题必将得到完善的解决,非正交多址技术也会在5G通信领域中得到广泛的应用。

User Assisted Cooperative Relaying in Beamspace Massive MIMO NOMA Based Systems for Millimeter Wave Communications

A novel scheme‘user assisted cooperative relaying in beamspace massive multiple input multiple output(M-MIMO)non-orthogonal multiple access(NOMA)system’has been proposed to improve coverage area,spectrum and energy efficiency for millimeter wave(mmWave)communications.A downlink system for M users,where base station(BS)is equipped with beamforming lens antenna structure having NRF radio frequency(RF)chains,has been considered.A dynamic cluster of users is formed within a beam and the intermediate users(in that cluster)between beam source and destination(user)act as relaying stations.By the use of successive interference cancellation(SIC)technique of NOMA within a cluster,the relaying stations relay the symbols with improved power to the destination.For maximizing achievable sum rate,transmit precoding and dynamic power allocation for both intra and inter beam power optimization are implemented.Simulations for performance evaluation are carried out to validate that the proposed system outperforms the conventional beamspace M-MIMO NOMA system for mmWave communications in terms of spectrum and energy efficiency.

Energy Efficient Transmission in Underlay CR-NOMA Networks Enabled by Reinforcement Learning

In order to improve the energy efficiency(EE)in the underlay cognitive radio(CR)networks,a power allocation strategy based on an actor-critic reinforcement learning is proposed,where a cluster of cognitive users(CUs)can simultaneously access to the same primary spectrum band under the interference constraints of the primary user(PU),by employing the non-orthogonal multiple access(NOMA)technique.In the proposed scheme,the optimization of the power allocation is formulated as a non-convex optimization problem.Additionally,the power allocation for different CUs is based on the actor-critic reinforcement learning model,in which the weighted data rate is set as the reward function,and the generated action strategy(i.e.the power allocation)is iteratively criticized and updated.Both the CU’s spectral efficiency and the PU’s interference constrains are considered in the training of the actor-critic reinforcement learning.Furthermore,the first order Taylor approximation as well as other manipulations are adopted to solve the power allocation optimization problem for the sake of considering the conventional channel conditions.According to the simulation results,we find that our scheme could achieve a higher spectral efficiency for the CUs compared to a benchmark scheme without learning process as well as the existing Q-learning based method,while the resultant interference affecting the PU transmission can be maintained at a given tolerated limit.

An Efcient Genetic Hybrid PAPR Technique for 5G Waveforms

Non-orthogonal multiple access(NOMA)is a strong contender multicarrier waveform technique for the fth generation(5G)communication system.The high peak-to-average power ratio(PAPR)is a serious concern in designing the NOMA waveform.However,the arrangement of NOMA is different from the orthogonal frequency division multiplexing.Thus,traditional reduction methods cannot be applied to NOMA.A partial transmission sequence(PTS)is commonly utilized to minimize the PAPR of the transmitting NOMA symbol.The choice phase aspect in the PTS is the only non-linear optimization obstacle that creates a huge computational complication due to the respective non-carrying sub-blocks in the unitary NOMA symbol.In this study,an efcient phase factor is proposed by presenting a novel bacterial foraging optimization algorithm(BFOA)for PTS(BFOA-PTS).The PAPR minimization is accomplished in a two-stage process.In the initial stage,PTS is applied to the NOMA signal,resulting in the partition of the NOMA signal into an act of sub-blocks.In the second stage,the best phase factor is generated using BFOA.The performance of the proposed BFOA-PTS is thoroughly investigated and compared to the traditional PTS.The simulation outcomes reveal that the BFOA-PTS efciently optimizes the PAPR performance with inconsequential complexity.The proposed method can signicantly offer a gain of 4.1 dB and low complexity compared with the traditional OFDM.

卫星通信网络功率域非正交多址技术研究综述

卫星通信网络正面临多用户、大容量、高效率的接入需求带来的挑战。非正交多址技术作为5G通信网络中提高接入用户数量与用户通信容量的关键技术,在卫星领域的应用受到了广泛的关注。以NOMA技术中的功率域NOMA(PD-NOMA)为研究重点,在介绍其基本原理的基础上,总结了卫星通信网络中该技术的研究现状,分析了应用存在的技术难点,提出了未来研究的发展趋势。