频谱异构认知无线电中基于吞吐量降的空时频谱机会感知

在认知无线电(CR)中,频谱感知是实现动态频谱接入的关键技术之一。为适当保护主用户并最大化次级用户的性能,目前大部分相关工作均是用虚报概率和漏检概率作为感知度量来确定最佳感知参数的。但这种度量是用主次用户的碰撞概率来衡量次级用户对主用户的影响的,没有考虑干扰强度的影响,仅适合同构频谱环境;在不同位置次级用户有不同接入机会的异构频谱环境中,并不能最大化频谱利用率。为此,该文首先定义了吞吐量降,并提出在异构频谱环境下采用吞吐量降作为一种新的感知度量。吞吐量降是指由于次级用户占用授权频谱而导致主用户吞吐量下降的百分比。在衡量次级用户对主用户的影响时,它综合了主次用户的碰撞概率和干扰强度两个因素;其次,研究了以吞吐量降为约束的次级用户吞吐量优化问题。最后,数值仿真证实了该方案比目前几种传统方案的频谱利用率显著提高。     

Optimal cooperative beamforming design in cognitive radio networks with multiple secondary user links

In this paper, a novel beamforming method is proposed for a more realistic cognitive radio system with several secondary transmitters and receivers, a number of relays, and 1 primary transmitter and receiver. When the primary user link is idle, all secondary transmitters access temporal spectrum holes to simultaneously broadcast their information to the relays each associated with an infinite buffer. In the next stage, the relays transmit the information to the secondary receivers using a cooperative beamforming method no matter whether primary user link is silent or not. The proposed method of designing the beamforming vector enables the system to maximize the power received by the secondary users while maintaining the interference plus noise power at the primary user receiver below a predefined threshold. Results of simulations confirm validity of the method and improved performance compared to the zero‐forcing beamforming. The impact of channel quality between nodes on the performance of the system is also investigated.     

Performance evaluation of sequential spectrum handoff in cognitive radio networks: a single‐user case

Powerful spectrum handover schemes enable cognitive radios to exploit transmission opportunities in primary users’ channels appropriately. In this paper, modeling and performance evaluation of sequential spectrum sensing strategy are addressed. To this end, the average number of handovers required for finding a transmission opportunity is evaluated assuming that a prior knowledge of the presence and absence probabilities of the primary users is available. Moreover, the average throughput maximization of a secondary user by optimizing its spectrum sensing time is formulated, and a set of illustrative numerical results is then presented to validate the analytical analysis.Copyright © 2013 John Wiley & Sons, Ltd.     

主用户活跃性对新的认知无线电系统容量的影响

在机会频谱接入认知无线电系统中,认知用户只有在通过感知确定信道空闲时才可以接入授权信道,因此频谱感知对于系统性能影响非常重要。本文提出了基于新帧结构的四元频谱感知模型,考虑主用户活跃性对认知网络吞吐量的影响,采用可同时最大化感知和数据传输时间的新帧结构模型,不需要考虑感知和吞吐量的均衡。理论分析新模型下感知时间,主用户活跃性,目标检测概率,主用户接收信噪比对系统吞吐量的影响,并与传统模型进行对比。     

使次系统容量最大化的协作频谱感知性能分析及优化

针对认知无线电网络中SU数、检测门限、带宽、频谱利用率和次系统容量间关系的分析表明,一方面C-CSS不仅可降低虚警率、提高频谱利用率,还可利用较少的SU实现较高的次系统容量;另一方面在SU数一定且满足目标要求时,C-CSS与T-CSS实现最大次系统容量所要求的检测门限不同.提出协作频谱感知优化算法,利用NP准则通过直接对数学模型求解即可得到使次系统容量最大的SU数和相应检测门限.理论分析和仿真结果均表明,所提算法在保证目标检测率的前提下最大化了次系统容量.     

Throughput performance under primary user emulation attack in cognitive radio networks

Spectrum sensing in cognitive radio networks imposes some security threats to the secondary users (SUs) such as primary user emulation attack (PUEA). In the present paper, throughput of an SU is studied for cognitive radio network under PUEA where SU spectrum access is hybrid, ie, either in overlay mode or in underlay mode. A novel analytical expression for throughput of an SU in presence of PUEA is developed. Impact of several parameters such as sensing time, attacker strength, attacker's presence probabilities, maximum allowable SU transmit power, and tolerable interference limit at primary user on the throughput of an SU is investigated. The throughput performance under PUEA and without PUEA is compared.     

认知无线电网络中基于主系统有限反馈的频谱共享方案

摘 要：提出一种频谱共享方案,该方案适用于同时存在多个主用户和一对次用户的场景。各主用户依据接收机反馈的有限信道质量信息（CQI, channel quality information）分配发送功率及传输速率。次用户根据偷听到的主系统CQI有限反馈,以适当的功率及速率接入信道。次用户接入信道的行为对各主用户造成一定干扰,以致主系统传输速率遭受一定损失。本文在主系统速率损失约束条件下,研究得出了使次系统吞吐量最大化的次用户发送功率及传输速率最佳分配方案。数值结果表明,对于每个主用户仅需反馈3-4个量化比特,次系统的有效吞吐量就可堪比于主次发射端均拥有主系统链路完整CQI的情况。仿真结果显示,所提出的频谱共享方案能够满足主系统速率损失约束。     

Dynamic control approaches of spectrum sensing in multi-band cognitive radio networks

In this paper,the dynamic control approaches for spectrum sensing are proposed,based on the theory that prediction is synonymous with data compression in computational learning. Firstly,a spectrum sensing sequence prediction scheme is proposed to reduce the spectrum sensing time and improve the throughput of secondary users. We use Ziv-Lempel data compression algorithm to design the prediction scheme,where spectrum band usage history is utilized. In addition,an iterative algorithm to find out the optimal number of spectrum bands allowed to sense is proposed,with the aim of maximizing the expected net reward of each secondary user in each time slot. Finally,extensive simulation results are shown to demonstrate the effectiveness of the proposed dynamic control approaches of spectrum sensing.     

主用户活跃性下的多功率分配策略

考虑到认知用户在信息传输过程中主用户的状态可能随时变化,提出了一种新的功率分配模式——多功率分配策略。在基于频谱感知的系统模型中,以认知系统的吞吐量为目标函数,得出了主用户感知过程的多种状态,并分配三种不同的功率,最大化认知系统的容量。仿真结果表明,随着主用户活跃指数的逐渐提高,所提新模型的功率分配策略要优于传统方法。同时分析了新的功率分配下平均干扰功率与主用户接收端的信噪比对系统吞吐量和最优感知时间的影响,进一步验证了所提出新策略的有效性。 〖HT5H〗关键词：〖HT5K〗认知无线电;主用户活跃;频谱感知分配;多功率分配;吞吐量最大化     

优化的最佳中继协作频谱感知

在基于中继的协作频谱感知中,尽管通过引入认知中继可有效提高协作频谱感知性能,然而认知中继的引入也会带来额外的系统开销及复杂度增加问题。为了节约系统开销,本文在前期取得研究成果的基础上,进一步提出了一种基于删余的最佳中继协作频谱感知方案,只有当次用户检测到主用户信号且目标次用户的报告信道衰落严重时,才申请认知中继的协作传输,同时目标次用户将其检测到的感知信息发送到认知中继;最后,分别从检测性能和次系统可获得的容量角度对所提方案下的协作频谱感知性能进行了理论分析。分析和仿真结果表明,所提方案可以有效提高检测性能,当确保主用户受到足够保护的前提下,利用所提方案可以获得更高的次系统容量。      

Prediction based channel allocation performance for cognitive radio

The interdependency, in a cognitive radio (CR) network, of spectrum sensing, occupancy modelling, channel switching and secondary user (SU) performance, is investigated. Achievable SU data throughput and primary user (PU) disruption rate have been examined for both theoretical test data as well as data obtained from real-world spectrum measurements done in Pretoria, South Africa. A channel switching simulator was developed to investigate SU performance, where a hidden Markov model (HMM) was employed to model and predict PU behaviour, from which proactive channel allocations could be made. Results show that CR performance may be improved if PU behaviour is accurately modelled, since accurate prediction allows the SU to make proactive channel switching decisions. It is further shown that a trade-off may exist between achievable SU throughput and average PU disruption rate. When using the prediction model, significant performance improvements, particularly under heavy traffic density conditions, of up to double the SU throughput and half the PU disruption rate were observed. Results obtained from a measurement campaign were comparable with those obtained from theoretical occupancy data, with an average similarity score of 95% for prediction accuracy, 90% for SU throughput and 70% for PU disruption rate.     

Effective throughput maximization for in-band sensing and transmission in cognitive radio networks

In cognitive radio networks, a secondary user is expected to utilize idle periods in a spectrum band but avoid interfering with busy periods occupied by primary users in the same band. To achieve the above goal, usually a secondary user periodically senses a spectrum band, and once an idle period is detected, the secondary user sends data in a transmission time. Due to (i) miss-detection of busy periods or (ii) unpredictable arrivals of busy periods, a secondary user may send data in busy periods, which causes useless data transmission. A secondary user usually cares about effective throughput which excludes the useless transmitted data. In order to alleviate the useless data transmission and enhance effective throughput, we consider dividing one long data transmission into two or more smaller data transmissions. Analyses, which are verified by simulations, are developed in this paper to calculate effective throughput in a periodic sensing structure with sensing errors. We use the analyses to select a set of parameters of sensing and transmission such that effective throughput is maximized at a certain load while the interference is below a pre-determined level. Besides, we study two policies, namely, fixed parameter policy and dynamic parameter policy, to maximize effective throughput in a spectrum band with variable loads; the former policy selects and applies one fixed set of parameters to different loads, but the latter policy uses different sets of parameters in different loads respectively. Numerical results show that the dynamic parameter policy outperforms the fixed parameter policy.     

认知无线电网络中用户行为建模综述

综述了近年来在认知无线电网络中用户行为建模的相关研究成果,第1部分主要论述了认知无线电网络中授权用户行为建模的相关方法及其模型,第2部分论述了认知无线电网络中认知用户行为建模的相关方法及其模型。提出未来的主要研究方向是研究授权用户行为、频谱空隙模式、认知用户行为、用户流特性这四者之间的内在联系及其相互之间的约束关系,揭示它们之间的本质联系。     

基于最优停止的认知无线网络下行频谱接入算法

为有效平衡认知无线网络中次用户系统中接入信道的感知时间和信道总的吞吐量之间的矛盾,提出了一种只对部分信道进行感知的频谱接入策略,联合总的感知信道数和各条信道的感知时间进行优化,并通过最优停止算法求解,在最大化节省感知时间的同时,取得较大的平均吞吐量。与HC-MAC(Hardware Constrained- Media Access Control)算法的仿真分析对比表明,该算法在相同给定条件下感知时间更短,吞吐量更大,具有明显的优势。     

认知网络中的能量回收技术：性能分析及优化设计

通信网络中有限的能源和频带资源限制了网络容量的进一步提升.对能量回收技术在认知网络中的应用进行研究,量化评估用户可回收的能量以及可达吞吐率,并进行优化设计很有必要.在所分析的系统中,当授权用户进行通信时,非授权用户可回收无线信号中所带有的能量,并利用回收的能量进行频谱检测;当检测到授权用户空闲时,非授权用户将接入频谱,利用回收到的能量进行数据传输.采用马尔科夫链模型对通信场景进行描述分析,发现授权用户的活跃程度对非授权用户可回收的能量、获得的传输机会带来影响,进而决定了非授权用户的可达吞吐量.在此基础上,提出一种通过控制授权用户业务量,以最大化网络能量效用和频谱效用的优化方案,并通过仿真证实了理论分析的正确性.     

一种基于感知信任度的加权协作感知算法

基于非协作感知的不确定性,协作频谱感知方法具有更高的可靠性.在传统的加权数据融合的基础上,根据无线电通信环境次用户(Secondary User,SU)的信任度不同,引入信任度函数及其信任度因子,提出了一种基于次用户信任度的自适应数据融合算法.仿真结果表明,该算法可以提高主用户(Primary User,PU)的检测概率,具有一定的可靠性和有效性,其检测性能优于传统的加权数据融合准则,同时还适应感知用户的拓扑变化.     

基于业务请求数据包长度的机会频谱接入算法

针对非时隙主用户网络,研究了单个次用户在周期性感知框架下的机会频谱接入问题。通过建立次用户信道感知和接入模型,提出了一种基于次用户请求业务数据包长度的机会频谱接入算法。该算法根据每个时隙分配给次用户业务数据包长度,自适应调整机会频谱接入策略。仿真结果表明,所提算法能够在干扰水平要求较高情况下,提高次用户平均有效传输吞吐量的同时,实现有效吞吐量与碰撞概率的折中;同时当外部环境发生变化时算法具有较强的鲁棒性。     

一种多用户协同频谱感知功率控制方案

分析和研究了多用户协同频谱感知原理,通过时分方式,实现了多用户之间的频谱共享。同时为避免对主用户产生有害的干扰,从用户通过一种算法控制它的发射功率,保证主用户的通信服务质量。最后对多用户协同频谱感知和单用户频谱感知的性能进行了仿真研究,结果表明多用户协同频谱感知可以明显提高频谱感知的性能,克服阴影/衰落作用的不利影响,提高频谱利用率。     

认知无线电网络主用户模仿攻击下次用户通信性能分析

随着认知无线电网络（CRN）技术的不断发展,安全问题日益受到重视。模仿主用户（PUE）是一种典型的易于实现且对CRN影响巨大的攻击行为,根据产生的原因、目的和过程的差异,可以分为恶意不端次用户PUE和自私不端次用户PUE 2类攻击。已有文献大多针对前者进行了分析,而对后者分析极少。重点对两者进行了区分,提出了四维连续时间马尔科夫链分析模型,详细地分析了自私不端次用户PUE攻击对正常次用户通信性能的影响,并对比了几类典型的PUE攻击检测技术。通过仿真结果可以看出：PUE攻击检测技术引入自私不端次用户检测机制极为必要,可以有效地改进检测效果。