中继协作下认知NOMA网络性能分析

把非正交多址接入（NOMA）技术应用到认知网络中,提出基于中继协作的底层认知NOMA系统模型。在瑞利衰落信道下,考虑一个两跳的通信网络,认知中继同时接收来自主网络发射源和次网络发射源的信号,并采用串行干扰消除策略解码转发接收到的信号。次级网络通过为主网络提供中继解码转发服务,获得接入授权频段的机会;主网络通过贡献出授权频段,换取次级网络协作通信的机会,同时获得了优先解码权,保证了主网络通信的可靠性。推导了系统各个接收端的中断概率闭合表达式,并进行了MATLAB仿真。仿真结果表明:采用中继协作可以有效提升认知NOMA网络的中断概率性能。      

两阶段中继选择策略下SWIPT-CR-NOMA网络的中断性能分析

针对采用无线携能传输(SWIPT)的多中继协作底层认知NOMA网络,提出一种基于NOMA和串行干扰消除协议的两阶段中继选择策略(TSRS),次级网络源节点和所选中继采用相同的功率分配生成多用户叠加信号,中继只利用采集能量提供解码转发服务。推导了用户中断概率的闭合表达式,进行了蒙特卡洛仿真验证,分析了功率分配因子、能量分裂参数、干扰温度限和中继数量等系统参数对中断性能的影响。仿真结果表明,所提方案可显著提升协作系统中断性能。      

非理想SIC下全双工NOMA系统的安全性能分析

针对存在多个非共谋窃听者,研究了一种基于全双工中继和两阶段中继选择（TSRS）的非正交多址接入（NOMA）物理层安全通信方案。每个通信过程包含一个传输时隙,系统在每个时隙开始由TSRS策略选择最优中继,所选中继在从源节点接收NOMA叠加信号的同时,向两个目的节点转发上一时隙的再编码叠加信号,两个目的节点采用串行干扰消除（SIC）技术从中继叠加信号中解码获取各自的期望信号。推导了非理想SIC下系统安全中断概率的近似表达式,进行了蒙特卡洛（Monte-Carlo）仿真验证,同时分析了各仿真参数（SIC残余干扰系数、目标安全速率、中继规模等）与系统安全中断概率的关系。理论分析与模拟仿真的结果表明,全双工技术与TSRS的结合方案能有效提升系统的安全中断性能。将该方案应用于实际通信系统设计时,选择合适传输信噪比（SNR）、提高串行干扰消除能力或适当增加中继数量均可实现更好的保密性能。      

多用户认知非正交多址接入系统中断性能分析及功率分配算法

非正交多址接入(NOMA)是5G网络关键候选技术之一,其与认知无线电(CR)技术相结合形成系统(CRNOMA),能够实现更高的频谱效率及更大的吞吐量。该文将直传与中继协同传输(CDRT)方案引入多用户CRNOMA系统,其中CDRT表示次级源(SS)直接与近端次级用户通信,而仅通过中继(R)与多个远端次级用户通信。在非理想自干扰消除和全双工(FD)中继情况下,推导了每个NOMA用户中断概率(OP)的精确闭式表达。此外,在该系统模型下分析SS, R和用户的收益最优化问题,提出一种基于收益的两阶段迭代功率分配算法。仿真结果显示,在高信噪比(30 dB)条件下,与随机功率分配及平均功率分配方案相比,该文所提算法的用户和速率、SS总收益、R总收益分别可最高提升13%, 56%及26%。蒙特卡罗仿真验证了理论分析与实验结果的一致性。     

两级中继选择的协作CR-NOMA网络性能分析

本文研究了中继选择方案对协作下认知非正交多址（CR-NOMA）网络中断性能的影响,提出了一种两级中继选择方案。第一时隙在保证主用户服务质量的基础上,次级网络源节点向认知中继集群广播叠加信号。第二时隙认知中继提供解码转发服务,协助源节点传输信息。基于上述假设,推导了次级用户中断概率的闭合表达式并给出了分析结果。证明相比于部分中继选择策略,两级中继选择策略可以达到更好的中断性能和更大的分集增益。同时本文的分析结果验证了备选中继节点数目和功率分配因子对系统中断性能的影响,蒙特卡罗仿真验证了理论结果。      

非理想SIC下SWIPT-CR-NOMA网络中断性能分析

针对采用无线携能通信的多中继底层协作认知非正交多址接入网络,提出一种两阶段中继选择策略。认知中继执行功率划分的无线携能通信协议为次级用户提供解码转发服务,其能量开销源于所采集到的能量。考虑了实际的非正交多址接入网络中,中继节点与次级用户均无法完全消除多址干扰,即无法实现理想连续干扰消除。在干扰阈值约束下,推导了非理想连续干扰消除下两次级用户端中断概率的精确表达式,并通过蒙特卡洛仿真验证其正确性。此外,定量分析了各系统相关参数（最大发射功率、干扰阈值、功率分配系数等）的选取对次级用户中断性能的具体影响。结果表明,在相同的系统参数设置下,所提方案次级用户中断性能远优于现有部分中继选择方案。      

自适应窃听下NOMA用户协作干扰的物理层安全研究

在存在一个半双工自适应窃听者的通信模型中,分析了采用非正交多址(Non-orthogonal Multiple Access,NOMA)技术合作系统的性能。提出了一种新型的合作NOMA方案,该方案在中继转发时,强用户可充当中继协助转发弱用户信号,而弱用户采用全双工技术向窃听者发送干扰信号,提高了通信链路的安全性和用户的服务质量。合法接收端采用连续干扰消除(SIC)技术,以解码来自叠加信号的各个消息。在已知窃听信道统计信道状态信息(CSI)的情况下,分别推导了2个用户的安全中断概率和中断概率的闭合表达式,并通过Monte-Carlo仿真验证。理论分析和数值模拟结果均表明所提出的NOMA用户合作方案在保密率方面优于非合作方案的性能。     

全双工协作多播业务在NOMA系统中的应用和性能

研究了多播业务在协作非正交多址接入（non-orthogonal multiple access,NOMA）系统中的应用及其性能。在一个单播和多播混合业务的场景中,多播用户组中选择某个信道状态最好的用户作为中继进行解码转发单播用户的信号,并在中继用户支持全双工的模式下,分析和推导了单播用户的中断概率和平均可达速率的闭式表达式。蒙特卡洛仿真结果和理论推导高度一致,表明提出的协作多播应用可以极大改善单播用户的中断性能,且多播用户的容量性能在中继发射功率不是很高的情况下不会受到影响。     

基于NOMA的协作中继网络安全性能分析

由于非正交多址接入(Non-orthogonal Multiple Access,NOMA)能够显著提升系统的频谱资源利用率,在下一代移动通信中得到广泛应用。对NOMA环境下多中继协作网络的最优中继选择方案和系统安全性能进行了分析和讨论,其中包含窃听者仅窃听中继和窃听者同时窃听中继及源节点这2种情况下的系统安全性能表现,并与相同场景下正交多址接入(Orthogonal Multiple Access,OMA)网络进行了对比。最终的理论分析和仿真结果表明,在所提出系统模型中,当信道条件相同时,NOMA网络总能取得相较于OMA网络更好的安全性能,同时随着系统中继节点数目的增多,NOMA网络在物理层安全性能上获得更大的优势。     

非正交多址接入系统中的联合中继选择和用户配对算法

针对多用户NOMA中继系统,文中提出了一种联合中继选择和用户配对算法。该算法首先利用最小距离准则选择最优次级用户与主用户配对,然后进行最优中继选择来改善系统中断性能。根据系统模型的分析,推导了系统中断概率的准确表达式,并分析了高信噪比条件下的渐近中断性能。系统分集阶数的研究说明了所提NOMA中继系统相比于传统单中继NOMA系统的优越性。最后,蒙特卡洛仿真结果验证了理论分析的正确性。     

Secrecy performance analysis on cooperative CR-NOMA network

In order to improve the secrecy performance of communication system and make efficient use of limited spectrum,overlay cognitive radio (OCR) technology was combined with non-orthogonal multiple access (NOMA) technology and the communication model was proposed,in which secondary network realized dynamic switching between assisting primary network communication and secondary network communication by sensing whether the primary user occupied the spectrum or not.Artificial noise (AN) aided technology was used in primary and secondary networks respectively to further improve the secrecy performance of the system.The secrecy performance of the system was studied by deducing the expressions of the primary and secondary network secrecy outage probability and secrecy throughput respectively.The simulation results show that the proposed cognitive cooperative NOMA communication scheme is beneficial in reducing secrecy outage probability and increasing secrecy throughput.Furthermore,the influence of AN power allocation factor on system performance is given.     

Research on the NOMA performance in cognitive cooperation network

The non-orthogonal multiple access (NOMA) technology was studied in a downlink cognitive relay cooperation network.A cognitive multiuser relay cooperation based NOMA scheme was proposed (CM-RC-NOMA),in which,the outage performance of PU and SU were given under different cognitive relay cooperation schemes and the corresponding outage expressions were also derived.At the same time,the AF based relay cooperation method and the DF based relay cooperation method were compared.The simulation results show that the lower outage of PU can be achieved by AF method compared with DF method,when the channel condition of BS to PU is no more than that of SU to PU.It is also revealed that the optimal outage performance of PU can be achieved by the proposed best cognitive relay cooperation scheme in contrast to the traditional best cognitive relay cooperation scheme.     

Analysis of Network Path Selection Based on Outage Probability in Cognitive Relay Networks

This paper evaluates the outage performance of cognitive relay networks with mutual interference between secondary users and primary users under the underlay approach, while adhering to the interference constraint on the primary user. A network path selection criterion, suitable for cognitive relay networks, is provided, from which we derive the outage probability expression of cognitive relay networks. It is shown that the outage probability considering the interference to secondary user from primary user is higher than that without considering the interference to secondary user from primary user. In addition, the outage probability is affected by key network parameters. We analyze network path selection method based on outage probability and prove that the interference to secondary user from primary user has a significant effect on the network path selection and can not be ignored in practical wireless communication environments. Simulation investigation is also provided and used to verify the theoretical analysis.     

Performance analysis of nonorthogonal multiple access‐based underlay cognitive relay network

This paper considers cooperative non‐orthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. A single‐cell downlink cooperative NOMA system has been considered for the secondary network, consisting of a base station (BS) and two secondary users, ie, a far user and a near user. The BS employs NOMA signaling to send messages for the two secondary users where the near user is enabled to act as a half‐duplex decode‐and‐forward (DF) relay for the far user. We derive exact expressions for the outage probability experienced by both the users and the outage probability of the secondary system assuming the links to experience independent, nonidentically distributed Rayleigh fading. Further, we analyze the ergodic rates of both the users and the ergodic sum rate of the secondary network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. Further, the interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis. The performance of the proposed CR NOMA network has been observed to be significantly better than a CR network that uses conventional orthogonal multiple access (OMA) scheme. The analytical results are validated by extensive simulation studies.     

Performance Analysis of Two-Way Hybrid Decode-and-Amplify Relaying Scheme with Relay Selection for Secondary Spectrum Access

In this paper, we propose and analyze the outage probability of a two-way hybrid decode-and-amplify relaying scheme with relay selection for secondary spectrum access. In this scheme, a secondary network is co-located and uses the same spectrum as the primary network. The primary network is comprised of two primary terminals that attempt to transmit signals to one another; the secondary network is comprised of M secondary transmitter-receiver pairs (ST-SR). One of the secondary transmitters chosen to cooperate with the primary network uses a hybrid decode-and-amplify forward technique in order to relay primary and secondary signals. We derive expressions for the outage probability of the primary network as well as the secondary network over a Rayleigh fading channel. Simulation results are presented to verify theoretical analyses and to compare the performance of the proposed protocol to that of a two-way direct transmission protocol.     

Performance Analysis of Decode-and-Forward Scheme with Relay Ordering for Secondary Spectrum Access

The communication efficiency of primary networks in cognitive radio depends on wireless environments, such as obstacles (e.g. buildings), distances between transmitter and receiver, and limited transmit power. A cooperative model between primary and secondary networks has the potential to overcome these problems. In this paper, we propose and analyze the performance of a decode-and-forward scheme with relay ordering for secondary spectrum access. In this scheme, a primary transmitter communicates with a primary receiver with the help of two secondary transmitters. Each secondary transmitter relays primary signals from the primary transmitter to primary receiver, and follows an optimal order to ensure the best communication capacity of the primary network and to find opportunities to transmit its own signals. The performance of primary and secondary networks is evaluated by theoretical analysis in terms of outage probability. Monte Carlo simulations are presented to verify the theoretical analysis and to compare the performance of the proposed protocol with that of a direct transmission protocol and a decode-and-forward protocol with a relay selection scheme.