Robust cooperative spectrum sensing schemes for fading channels in cognitive radio networks

In cognitive radio systems, cooperative spectrum sensing can detect the presence of the primary user accurately. In practice, however, since the sensing observations are forwarded to a data collector through fading channels, the sensing performance is severely degraded. To deal with this problem, in this paper, we first propose a secondary user selection based cooperative spectrum sensing method to improve sensing performance by decreasing the reporting errors introduced by the fading channels. Mo...     

衰落信道下提高协作频谱感知能力的方法

由于协作频谱感知能够更准确地确定主用户的存在与否,因此,它被认为是认知无线电技术中的一个重要研究分支.在协作频谱感知中,各认知用户需要通过报告信道发送其本地判决结果(0或1)到融合中心(FC).然而,在实际中,报告信道通常受衰落的影响,这将降低频谱感知的检测性能.针对这个问题,首先,文中提出一种基于认知用户选择的协作频谱感知算法.该算法通过减小由衰落信道引入的误码概率来提高协作频谱感知的检测性能.其基本思想为:只有具有较好瞬时信道增益报告信道的认知用户才将其本地二进制判决结果发送到FC,否则,该认知用户不发送其本地检测结果到FC.其次,提出一种基于空时编码的协作频谱感知方法.通过在CR网络中,利用空间分集增益来降低由衰落型报告信道引入的误码概率,从而提高检测性能.最后,对提出的这两种协作频谱感知方法的检测性能进行理论分析研究,并对其进行数值仿真.仿真结果表明:相比于传统的协作频谱感知,本文提出的这两种协作频谱感知算法都能提高对主用户的检测性能.     

认知无线电网络中的分布式协作感知算法*

针对认知无线电中频谱感知的问题,讨论了分布式协作感知场景下最优的感知算法。介绍了经典的基于放大前传（AF）、解码前传（DF）和选择中继（SR）的分布式协作方案,包括模型、检测概率和虚警概率。提出了一种新的分布式协作感知算法,该算法将原始统计量和信噪比发送给协作用户,减少信道噪声对最后决策结果的影响。运用似然比准则推导出了最优的加权系数,以及决策函数。对几种协作方案的中断概率进行理论推导,并用数值仿真的方法验证了算法在中断概率上的性能。仿真结果表明,提出的方法在检测概率和中断概率上远优于其他分布式协作方案,但该方法需要协作用户间无损耗的传输,这也给实际的应用提出了很大的挑战。     

认知无线电中基于多址接入信道的多用户联合频谱感知算法

针对多用户联合感知场景问题,考虑次用户至决策中心之间有损信道的情况,提出了基于多址接入信道（MAC）的联合频谱感知算法。在系统结构和数学建模基础上,分析了传统MAC算法渐近性、中断概率等性能。在次用户平均发射功率约束下,以最大化检测概率为目标,对基于MAC算法中的发射增益进行优化;并考虑了一定服务质量情况下最小化次用户数目的问题。仿真结果表明,MAC算法能够保证良好的检测性能,以决策中心错误概率为例,提出的优化算法取得了指数级的性能提升。     

Cooperative spectrum sensing based on stochastic resonance in cognitive radio networks

A new censoring cooperative spectrum sensing scheme based on stochastic resonance(SR)technique in cognitive radio(CR)network is proposed in this paper.The observations of the cooperative secondary users(SUs)whose statistics fall into the censoring interval are processed by SR system in the proposed scheme.The hard fusion and the soft fusion for the censoring cooperative spectrum sensing scheme are analyzed respectively.Theoretical analyses and simulation results show that the proposed censoring cooperative spectrum sensing scheme has the same detection performance as and lower computational complexity than the method that each cooperative SU performs spectrum sensing using SR-based energy detection,and its detection performance is superior to that of the conventional method that all the cooperative SUs perform spectrum sensing using energy detection in hard fusion.In soft fusion,the proposed censoring cooperative spectrum sensing based on equal gain combination can achieve the optimal sensing performance approximately.     

认知无线电中基于特征值检测的频谱感知算法

频谱感知的任务在于利用感知节点(无线传感器或者认知用户)采集的数据判断频谱空洞是否存在。基于最大特征值检测(MED)和最小特征值检测(SED)的方法最近被应用到频谱感知当中。这两种算法在检测实际应用当中普遍存在的相关信号时表现出良好的检测性能。然而,MED和SED算法对应的判决门限求解非常复杂,从而限制了它们在实际的认知无线电频谱感知中的应用。该文利用取样协方差矩阵的所有特征值,提出了一种新的基于特征值检测(ESD)的算法。利用多元统计理论获得了相应的判决门限。ESD算法无需主信号和无线信道信息参与感知过程。与此同时,它保留了与MED和SED相同的计算复杂度。更重要的是ESD算法对应的判决门限可以通过一个简单的闭合表达式进行求解,其计算复杂度低。仿真结果验证了新算法的有效性。     

Detection time analysis for the multiple-user cooperative spectrum sensing scheme in cognitive radio networks

In this paper, a novel multiple-user cooperative spectrum sensing (MCSS) scheme is proposed to achieve the spatial diversity gains for cognitive radio (CR) networks, where only the best relay, selected among all the candidate relays in accordance with the quality of channel conditions, is utilized to cooperatively detect the primary user. Closed-form expressions of detection time for the traditional non-cooperative and the proposed MCSS schemes are derived over Rayleigh fading channels. In addition, numeric...     

Distributed cooperative spectrum sensing in cognitive radio for ad hoc networks

Cognitive radio refers to an intelligent radio with the capability of sensing the radio environment and dynamically reconfiguring the operating parameters. Recent research has focused on using cognitive radios in ad hoc environments. Spectrum sensing is the most important aspect of successful cognitive radio ad hoc network deployment to overcome spectrum scarcity. Multiple cognitive radio users can cooperate to sense the primary user and improve sensing performance. Cognitive radio ad hoc networks are dynamic in nature and have no central point for data fusion. In this paper, gradient-based fully distributed cooperative spectrum sensing in cognitive radio is proposed for ad hoc networks. The licensed band used for TV transmission is considered the primary user. The gradient field changes with the energy sensed by cognitive radios, and the gradient is calculated based on the components, which include energy sensed by secondary users and received from neighbors. The proposed scheme was evaluated from the perspective of reliable sensing, convergence time, and energy consumption. Simulation results demonstrated the effectiveness of the proposed scheme.     

认知无线电网络中安全的协作频谱检测算法

在认知无线电网络中,当认知用户存在虚假感知信息SSDF时,协作频谱感知的性能会受到巨大影响。为了确保频谱感知的鲁棒性,提出了一种基于信誉度加权序贯频谱检测算法来识别恶意用户并减轻他们造成的影响。该算法通过使用认知用户的近期感知信息计算本地信誉度函数,再综合考虑其信誉值与感知过程中表现的稳定程度以消除恶意用户对主用户的传输效率带来的影响。仿真结果表明,在恶意攻击环境下,新算法优于现有典型协作频谱感知算法。     

基于可信度的认知无线电协同频谱检测

认知无线电中随着参与协同检测的认知用户数目的增大,频谱检测性能逐渐增强。但是过多的认知用户参与协同检测,会使整个认知无线电网络的灵敏度降低,同时也会造成巨大的系统开销。针对上述问题,提出了一种新的基于可信度的协同频谱检测方法。在满足目标错误概率的条件下,该算法只选择可信度较高的一些认知用户参与协同频谱检测。仿真结果表明当认知用户中存在恶意节点或者故障节点时,该算法同传统算法相比较,频谱检测性能更好,具有更强的健壮性。     

一种新型的认知无线电合作频谱感知算法*

为了提高认知无线电频谱感知性能,同时考虑到不同认知用户SU(Secondary User)具有不同的感知贡献和谈判力量,该文利用合作博弈理论提出了一种新的基于认知无线电的合作频谱感知非对称纳什谈判算法ANBS(Asymmetric Nash Bargaining Solution),该算法充分考虑到了每一个认知用户的感知可信度不尽相同的情况。仿真结果表明,与NBS(Nash Bargaining Solution)等算法相比,该算法不仅具有更强的合理性和可靠性,而且使系统整体感知性能得到了较大提高。     

一种时域—码域联合的认知无线电频谱感知算法

为了提高认知无线电系统中频谱感知的性能,对多维联合的频谱感知进行了研究,提出一种时域—码域联合的频谱感知算法。该算法主要利用了直接序列扩频主用户信号频谱空间中时域与码域的特性,分别从时域与码域的角度对信道的状态进行检测,其中时域采用能量感知,码域分析扩频主用户信号的二次功率谱,最终共同确认信道状态。仿真结果表明,联合感知算法对应的检测性能优于单纯时域或码域感知,能够直接应用于直接序列扩频主用户的频谱感知。     

认知无线电网络分布式多信道MAC协议*

在认知无线电网络中,MAC协议用于信道感知、选择和接入控制。以单网卡多信道MAC（MMAC）协议为基础,依据IEEE 802.22标准定义的静默期管理的两阶段感知策略,提出一种认知无线电网络分布式多信道MAC（CR-MMAC）协议。将两阶段感知机制和分布式协商融入MMAC协议,利用空闲频谱进行数据传输,并在MMAC协议ATIM窗的数据信道协商阶段引入预约机制,以避免选择同一信道的认知节点对在后续数据传输阶段再利用CSMA/CA造成的竞争碰撞。仿真对比分析表明,CR-MMAC协议能提高网络吞吐量、降低通信时     

一种基于特征值的多天线认知无线电盲感知算法

当不存在噪声不确定性时,频谱感知算法中能量检测法是较优的,但实际中噪声是无法确切估计的。针对这一问题,提出了一种适合多天线认知无线电系统的盲感知算法。该算法不需要主用户的任何先验知识,利用采样协方差矩阵的最大特征值和矩阵迹之比作为判决统计量来检测主用户信号。根据随机矩阵理论,当给定虚警概率时,可以求出判决门限的渐近式表达式。仿真结果表明,与同类算法相比,所提算法能获得较高的检测概率和较低的虚警概率,同时克服了能量检测法对噪声的敏感性。     

协作频谱感知的系统效用优化分析

协作频谱感知可以提升认知无线电的频谱感知能力,但不同的系统参数对协作频谱感知系统的性能会产生不同的影响。在综合考虑系统资源利用率和归一化吞吐量的情况下,对不同条件下用户数和感知时长对系统性能的影响进行分析。并在检测概率约束条件下,对结合系统检测概率和归一化吞吐量的系统效用提出优化方法,可以求出满足条件的最大系统效用值。仿真结果表明,在不同的环境和条件限制下,达到最大系统效用所需要的用户数和感知时长也是不同的。     

认知OFDM系统中基于能耗受限的频谱感知方法

针对传统频谱感知方法没有考虑能耗受限对认知系统的影响,以认知正交频分复用(OFDM)系统为背景,提出一种基于能耗受限的联合优化频谱感知方法。该方法基于传统能量检测方法,以最大化吞吐量性能为目标,将频谱感知问题建模为一个优化问题,联合多个频带选取最优感知时间和判决门限参数,使其在能耗受限的情况下,总吞吐量达到最大。仿真结果表明,与传统使用能耗均分的检测方法相比,该方法具有更大的吞吐量,能够更好地节约能耗。     

A weighted cooperative spectrum sensing framework for infrastructure-based cognitive radio networks

Spectrum sensing plays a critical role in cognitive radio networks. A good sensing scheme can reduce the false alarm probability and the miss detection probability, and thus improves spectrum utilization. This paper presents a weighted cooperative spectrum sensing framework for infrastructure-based cognitive radio networks, to increase the spectrum sensing accuracy. The framework contains two modules. In the first module, each cognitive radio performs local spectrum sensing and computes the total error probability, which combines the false alarm probability and the miss detection probability. The total error probability and the energy signal from the primary user are then sent to the base station. In the second module, the base station makes a final decision after combining the weighted energy signals from all cognitive radios. The final decision is then broadcasted back to all cognitive radios. To reduce the computation complexity and communication overhead, the base station also instructs the cognitive radios that have large total error probabilities not to report their local sensing results. We have developed a theoretical model for the proposed framework, and derived the optimal detection threshold, as well as the minimum number of cognitive radios required to participate in cooperative sensing, subject to a given total error probability. Numerical results verify that the proposed weighted cooperative spectrum sensing framework significantly improves the sensing accuracy.     

面向移动自组网的分布式认知MAC协议改进设计

针对移动自组网MAC协议未考虑节点移动性、缺乏功率控制机制、算法开销较大等问题,改进设计基于信道可维持时间的分布式认知MAC协议。新协议建立了节点存储信息结构,根据节点功率与移动速度的关系,构建信道可维持时间模型,并改进信道感知和数据传输算法,增加移动性和信道增益考虑,降低速度和功率对信道感知的影响,提高协议对移动性的适应能力。结果表明,对于中低速网络而言,该协议在不增加控制开销的基础上,丢包率、时延和频谱利用率等性能得到较大改善。