认知无线网络中一种基于放大转发的协作传输策略

在不干扰主用户数据传输的条件下,通过次用户间的彼此协作传输,可以使认知无线网络获得明显的空间和时间分集增益,从而改善次用户传输性能。该文针对主次用户共存,主用户交替转移信道忙闲状态的网络环境下,提出了一种基于放大转发的协作传输方案,当主用户存在时机会的使用中继节点转发数据,并且对所提方案的无冲突传输时间进行了理论分析,给出了非协作传输和协作传输模式下的无冲突传输时间的解析表达式,理论分析和仿真结果表明,协作传输方案的无冲突传输时间明显优于非协作传输方案,次用户协作为认知无线网络带来可观的性能增益。     

一种认知无线网络中的协作感知优化方法

认知无线电技术能够显著提高频谱资源的利用率,因此越来越受到学术界的关注。频谱感知是认知无线电的基础,一方面它要求能够快速找到可用频谱,另一方面当授权用户返回时又要求能够快速释放信道避免干扰。提出了一种认知无线网络中多用户协作感知分级方法,并通过数学推导给出最优的分级策略。仿真结果表明,采用所提出的协作频谱感知方法,能够提高认知无线网络的吞吐量。     

放大转发认知中继协作系统中继增益分配方案和性能分析

由于在传统的放大转发认知中继协作方案中,中继增益因子的分配只考虑了部分主、从系统参数,使得系统的能量效率较低、系统资源未被充分利用。为此,基于主系统传输速率约束和从系统终端接收信号平均误符号率最小准则,文章提出了一个新颖的中继增益最优化分配方案,获得了中继增益最优化精确解以及相应的上、下限封闭解析解;并基于获得的最优化中继增益,分析了系统的平均误符号率。结果表明,文章所获得的中继增益因子分配方案由于不仅考虑了从信源功率和从信源-中继链路增益,而且还综合考虑了中继-从信宿链路和主系统参数,可以实现系统资源的最优化配置,系统性能得到改善。      

认知无线电网络的一种协作频谱感知方案

认知无线电技术能够让非授权用户利用已经分配给授权用户的频段.为了不对首要用户的工作造成干扰,认知用户需要对频谱进行不间断的监测来判断首要用户是否存在.因此,频谱的感知是认知无线电技术的关键.协作频谱感知能够充分的利用网络资源,提高网络中的认知用户的检测概率.文中笔者简单地介绍了一种协作频谱感知的方案.仿真结果表明,通过该方法能够提高网络中认知用户的检测概率,提高网络的检测灵敏度.     

一种基于源端网络编码和交替传输的中继协作方案

针对源节点通过两个中继向目的节点发送数据的无线通信系统,为了减小传统中继协作方案的复用损失,提出了一种将源端网络编码和交替传输有效结合起来的新方案,称为交替源端网络编码(SSNC)。该方案在源端每三个时隙对发送数据进行一次网络编码,并且两个中继在相邻的时隙中交替的发送和接收数据,每个时隙中,一个中继接收源端数据的同时另一个中继转发上一个时隙其接收到的数据给目的端。通过对该方案的中断概率和分集复用折中性能的推导和分析,发现该方案相对于传统的重复编码和分布式空时码方案在获得相同分集阶数的情况下有更高的传输效率,在实际的通信系统中可以兼顾性能和效率。仿真结果证实了我们的结论。      

基于解码重传的最佳协作中继选择策略

近年来提出的协作分集技术通过使网络中各单天线用户共享彼此天线以形成虚拟多天线阵列,从而可以显著提高网络容量,也使得其备受科研工作者的关注。提出了基于解码重传（DaF）下的被动式最佳协作中继选择准则,该准则是通过推导协作中继传输系统的误符号率而得出的。在总功率限制下,可以证明基于解码重传下的机会中继在中断性能上考虑是最佳的,更确切地说,它的中断性能和利用全部候选中继传输的最佳解码重传策略是一样的。     

协作通信中一种改进的最佳中继选择算法

已有研究结果表明,机会中继可以获得与更为复杂的空时编码协作通信相同的分集增益。但是,随着可选中继节点数的增多,发生冲突从而导致选择失败的概率也明显变大。本文提出了一种改进的最佳中继选择算法,源站收到最佳中继发出的标志分组后发送选择确认消息,中继节点在冲突发生后进行退避。分析结果证明,采用新算法可以大大降低选择失败的概率,而增加的开销却很小。     

认知无线电中协作中继技术的研究

在无线通信环境中,衰落、多径和节点的移动都会导致通信环境较差,这些因素严重地影响了通信质量。当系统中有协作中继参与时,主用户可以通过共享中继的多根天线来获得增益完成通信从而有效抵抗了无线环境中的不良因素影响。本文建立了一个进行双向通信的主用户需要中继协助才可以完成通信的协作模型。并且定义中继采用放大转发的方式帮助主用户传输数据。本文理论分析了各个节点的中断概率,并通过仿真结果表明,本文提出的中继传输方法不仅使得主用户有效的完成了通信而且还减小了主用户的中断概率。     

认知无线网络中的协作通信技术

21世纪,随着信息技术的迅速发展,无线网络通讯信息技术也在不断更新和进步.然而频谱资源是有限的,快速发展的同时也带来了资源紧缺无法满足需求的状况.应运而生的无线认知网络技术,成为缓解频谱资源供不应求局面的新突破口.认知无线网络中的协作通信技术,能够增强对环境的掌控能力,提高智能化的程度.     

基于多维资源自适应分配的协作认知传输机制

该文针对协作认知无线电网络提出一种时域、频域和空域资源联合分配的传输机制,在改善授权用户传输性能的前提下使参与协作的认知用户获得合理的回报。所提机制利用多天线认知节点担任中继,通过自适应的时隙划分与带宽分配,对两跳传输链路中的瓶颈予以消除;并在包含多个协作认知用户的场景中,给出一种考虑公平性的中继选择算法。该方法一方面采用比例公平的思想实现认知用户间的公平性,另一方面通过调整奖励因子,使中继获得合理的回报。仿真结果表明,所提算法能够改善授权与认知系统的数据速率,同时给予认知中继公平的回报。     

认知无线电网络用户合作机会接入方案的研究

认知无线电技术可以用来解决随着无线通信的迅速发展而突显出来的频谱实际利用率不高的问题,并缓解频谱分配紧张的局面.本文所关注的是多个认知无线电用户(SU)的机会频谱接入问题.分布式认知无线电网络中,为避免和授权用户(PU)发生冲突,通常采用周期性感知方法,这将使吞吐量降低.本文提出了一种认知无线电用户间高效的合作方案.文中分析了用户合作的最好和最坏两种情况下系统吞吐量的解析解.通过仿真验证了理论结果,并比较分析几种方案下每个用户和系统吞吐量随用户数量的变化,得出了用户间有效的合作可以提高各自以及整个系统的吞吐量的结论.     

CRN中一种优化的数据传输方案

在认知无线电网络(CRN)中,如何有效地实现认知用户间快速可靠的数据传输是目前的研究热点。针对现有传输方案的不足,提出了一种优化的数据传输方案。在考虑节点发射功率和负载均衡的约束条件下,基于对认知用户间链路可靠性预测,联合频谱分配与按需路由策略实现认知用户数据的最优化传输。仿真实验表明,在减少路由重构次数的同时,较大地提高了系统的吞吐量。     

Fault-Tolerant Cooperative Spectrum Sensing Scheme for Cognitive Radio Networks

In order to solve the uncertainty resulting from shadowing effect and resist the attack from malicious cognitive radio (CR) users, we propose a fault-tolerant cooperative spectrum sensing scheme for CR networks, where an energy detection-based local spectrum sensing is performed at each CR user, a coefficient is used to weight each CR user’s sensing result, a linear weighted fusion process is performed at the fusion center (FC) to combine received sensing results. For a fault-tolerant cooperative spectrum sensing scheme, the most important issue is to distinguish whether the CR user is reliable or not. In this paper, a reputation-based cooperative mechanism is presented to alleviate the influence of the unreliable sensing results from CR users suffering shadowing and the false sensing data from malicious CR users on the detection result at the FC. In proposed fault-tolerant cooperative scheme, each cooperative CR user has a reputation degree which is initialized and adjusted by the FC and used to weight the sensing result from the corresponding user in the fusion process at the FC. And then, two reputation degree adjusting methods are presented to manage the reputation degree of each CR user. Simulation results show that the proposed scheme can not only weaken the harmful influence caused by malicious CR users, but also alleviate the corrupted detection problem resulting from destructive channel condition between the primary transmitter and the CR user. Moreover, the detection performance of the fault-tolerant cooperative scheme, which has a feasible computational complexity and needs no instantaneous SNRs, is close to that of the optimal scheme.     

Identifying Malicious Secondary User Presence Within Primary User Range in Cognitive Radio Networks

Wireless Personal Communications - Cognitive Radio (CR) Network is a wireless communication technology, in which a detection device smartly detects occupied and unoccupied channels. During traffic,...     

Reputation-Based Hierarchically Cooperative Spectrum Sensing Scheme in Cognitive Radio Networks

Cooperative spectrum sensing in cog- nitive radio is investigated to improve the det- ection performance of Primary User （PU）. Meanwhile, cluster-based hierarchical coop- eration is introduced for reducing the overhead as well as maintaining a certain level of sens- ing performance. However, in existing hierar- chically cooperative spectrum sensing algo- rithms, the robustness problem of the system is seldom considered. In this paper, we pro- pose a reputation-based hierarchically coop- erative spectrum sensing scheme in Cognitive Radio Networks （CRNs）. Before spectrum sensing, clusters are grouped based on the location correlation coefficients of Secondary Users （SUs）. In the proposed scheme, there are two levels of cooperation, the first one is performed within a cluster and the second one is carried out among clusters. With the reputa- tion mechanism and modified MAJORITY rule in the second level cooperation, the pro- posed scheme can not only relieve the influ- ence of the shadowing, but also eliminate the impact of the PU emulation attack on a rela- tively large scale. Simulation results show that, in the scenarios with deep-shadowing or mul- tiple attacked SUs, our proposed scheme ach- ieves a better tradeoff between the system robustness and the energy saving compared with those conventionally cooperative sensing schemes.     

Delay QoS Guaranteed Cooperative Double-Threshold Sensing Scheme in Cognitive Radio Networks

In cognitive radio networks, cooperation can greatly improve the performance of spectrum sensing. This paper proposes a delay (QoS) quality-of-service guaranteed cooperative spectrum sensing frame structure in which secondary users (SUs) conduct spectrum sensing and data transmission concurrently over two different parts of the primary user spectrum band. A double-threshold sensing scheme is employed in the local sensing step, only the SUs with reliable sensing information are allowed to transmit their “one bit” local decisions to the fusion center. The sensing performance and the SU transmission delay are analyzed in detail in this paper. Computer simulations show that the delay QoS guaranteed cooperative double-threshold sensing scheme could not only decrease the SU transmission delay but also save the reporting overhead of the SUs compared with the conventional detection method with one threshold.     

Optimal Cooperative Inactive Secondary Sensing Order Using Users in Cognitive Radio Networks

A novel cooperative spectrum sensing or- der which utilizes inactive Secondary users （SUs） efficiently based on maximum throughput has been proposed in Cog- nitive radio networks （CRNs）. In order to predict the states of Primary users （PUs）, we build the PU＇s traffic pattern as a Continuous-time Markov chain （CTMC） pro- cess. CRNs obtain the maximum throughput while SUs sense the licensed channels with the optimal order. The numerical simulation results show that the proposed or- der based on spectrum sensing scheme can achieve larger channel utilization and lower sensing overhead as compared with the spectrum sensing scheme without using the opti- mal order sensing. After considering the report overhead of SUs, the optimal number of inactive SUs for the maxi- mum throughput can be found.