基于载波检测的认知无线电方案设计与实现

针对目前认知无线电概念较少付诸实施的实际情况,对认知无线网络中非授权用户接入频谱空隙的具体方法进行研究,提出一种基于载波检测的设计方案.该设计硬件上由单片机和射频发射模块组成.软件上通过基于载波检测的程序设计来实现非授权用户的智能接入.经测试,所设计的接入算法使得非授权用户能够准确检测和访问处于空闲状态的频点,并在这个频点上成功进行数据的发送与接收.而当授权用户使用该授权频段时,非授权用户又能够及时退出,寻找新的频点.从而初步实现了同构网络中非授权用户的智能接入,完成了一个可使用的认知用户通信系统.     

基于深度强化学习的认知无线电协作频谱感知

为了解决频谱资源利用率低的问题,引入了认知无线网络的概念.在认知无线网络中,次要用户可以在不影响主要用户正常工作的前提下机会性地接入授权频段,故精确地感知频谱的状态并快速准确地接入授权频段就显得尤为重要.由于网络中存在干扰和阴影衰落等因素,传统的频谱感知效果不理想.本文引入了协作频谱感知技术,通过强化学习算法选择参与协...     

一种基于主动避让的认知无线网络路由维护方案

在认知无线电网络中,主用户使用授权频段时认知用户需要避让。这将导致认知用户原路由上工作频率的频繁切换。为了尽量减少这种切换,维持原路由上数据持续高效地传输,提出了一种优化的认知无线网络路由维护方案。在认知无线网络中,当认知用户测得主用户存在时先测试主用户的运动速度、运动方向等信息,继而根据主用户实际的运动情况判断认知用户是否可以避让。仿真结果显示,认知用户通过有效的避让既避免了对主用户的干扰,又维持了认知网络原路由继续工作。     

衰落信道下无线多跳网络的连通性研究

基于齐次泊松点过程的节点分布模型,在不同的衰落信道模型下推导了网络无孤立点概率的闭型表达式,用作网络连通概率的上界。特别分析了对数正态阴影衰落和瑞利衰落信道的相关物理参数对连通性的影响。此外,还讨论了协作通信对于网络连通性能的提高作用。最后,在仿真构造的无线网络中测试得到的连通性能的仿真值与理论分析结果吻合。     

认知无线电网络中基于智能天线的空间频谱接入机会

认知无线电技术可以动态使用授权频段进行传输,因此如何有效利用这些频谱接入机会成为一个研究重点。本文研究在认知无线电网络中使用智能天线,使认知用户在时域上获得频谱接入能力外,还具有增强的空间复用能力。当前频段出现活跃授权用户时,认知用户可以优化天线波束模式,避免干扰授权用户同时保持在该频段上的传输。本文对波束调整的策略进行分析,并给出了使用这些策略时认知用户可以获得的空间共享概率。理论分析和仿真结果均表明,使用智能天线可以使认知用户获得更多的频谱接入机会,频段的利用率大幅提高。     

边界节点对无线传感器网络连通性的影响

无线传感器网络的连通性是确保节点成功组网的基础,相对于内部节点,边界节点对无线传感器网络的连通性有着更大的影响.本文以节点的有效通讯面积为基础,通过理论推导,分析了边界节点的连通性和网络的整体连通性,而后通过仿真研究,分析了存在边界节点与消除边界效应后的网络连通度分布、连通度期望和网络是κ点连通的概率,从而说明了边界节...     

衰落信道下车载自组织网络连通性分析

以孤立节点数、最大连通长度、全局网络效率等参数为连通性量化指标,应用VanetMobisim车辆仿真软件建立车载自组织网络,详细研究在Nakagami衰落信道模型和确定信道模型下VANETs连通性随时间的演化特征。结果表明当VANETs全连通时,网络时间相关性较弱,当网络连通性比较差时,各项连通性指标均呈现重尾现象,网络连通性具有很强的时间相关性。分析车辆节点密度、路径损耗指数和衰落因子等因素对网络连通性的影响。     

基于SC-FDMA的宽带认知无线电网络中最优功率分配的研究

研究了基于单载波频分多址(SC-FDMA)的宽带认知无线电网络中非授权用户(NU)的最优功率分配(OPA)问题.首先给出了基于SC-FDMA的宽带认知无线电网络中非授权用户对授权用户的干扰功率模型.在此基础上,分别在下述两种约束条件下利用凸优化理论推导出了两种使非授权用户的和速率最大的最优功率分配(OPA)算法.约束条件一为:任一非授权用户的任一子载波对授权用户的干扰功率受限(IPCs);约束条件二为:所有非授权用户的所有子载波对授权用户的干扰功率受限(IPC).仿真结果表明,与等功率分配(EPA)和传统最优功率分配(C-OPA)算法相比,所提出的算法显著提高了非授权用户的可达和速率.     

移动无线传感器网络连通性自主恢复算法

无线传感器网络(WSNs)中关键节点故障会将网络分割成多个不连通的分区,给网络性能带来严重影响.而无线传感器网络往往布置在人工难以干预的偏僻恶劣环境中,网络连通性的自主恢复尤其重要.提出一种自主网络分区检测和连通性恢复(APDCR)策略,容忍无线传感器网络中关键节点的故障.APDCR首先基于1跳邻居和部分2跳邻居信息提出一种新的关键节点识别算法,然后给出关键节点的备用节点的选取算法和网络连通性恢复算法,最后扩展算法处理两个节点同时故障时网络不连通问题(2-APDCR).模拟实验结果表明了算法APDCR的有效性.     

异构无线网络负载均衡研究*

针对异构网络中的带宽分配及网络的负载均衡问题,提出了一种异构无线网络负载均衡的联合优化模型,该模型在一定条件下利用用户的带宽进行负载成本和网络效用的建立,并通过求解网络与用户的关联矩阵来得到带宽在网络中的优化分配方案,使异构无线网络达到负载均衡。仿真结果表明,联合优化模型的结果在最小化负载成本以及优化网络总效用性能之间,它让用户通过在不同网络间的切换使网络带宽优化分配、网络负载达到均衡。     

A network flow based approach for network selection in dynamic spectrum access networks

In this paper, we present a network flow based approach for dynamic network and channel selection for secondary users in dynamic spectrum access networks. Most approaches in the current literature on dynamic spectrum access networks do not consider dynamic network and channel selection. We present a network flow framework for network selection. We show that our approach can enable re-assignment of networks to secondary users and also re-assignment of channels to secondary users within the same network. The assignments and re-assignments take into account, the interference caused to primary users, the price each secondary user is willing to pay and the quality of service (QoS) obtained by each secondary user. We obtain a bound for the maximum number of re-assignments.     

跨洋航空网络的频谱共享博弈模型

提出一种跨洋航空网络中主干网络的频谱共享博弈模型。该模型综合考虑了主用户和所有次级用户的收益,主用户可在保证自身收益最大的前提下对各次级用户进行有效的频谱分配;各次级用户根据主用户的最佳单位定价改变请求带宽以获得最大收益。给出了该模型的静态博弈纳什均衡与动态博弈收敛结果,通过与次级用户收益的最优化模型进行比较,验证了用该模型解决跨洋航空网络中主干网络上的频谱分配问题具有公平性。     

一种认知无线电网络接入控制和功率控制联合设计

在underlay频谱共享模式下,提出一种认知无线电网络接入控制和功率控制的联合算法。该算法针对主用户干扰温度和次用户信号干扰噪声比(SINR)限制,通过引入冲突因子,实现网络自适应调整被拒绝参与频谱共享的次用户数目,通过迭代进行接入控制和功率分配实现频谱共享。仿真结果表明,该算法能够保证接入共享主网络频带的次用户数近似最优,而且缩短了接入控制的时间。     

非完美感知条件下认知网络的性能分析

通过对非理想频谱感知下的认知无线电网络(CognitiveRadioNetwork,CRN)建模,分析了认知网络的主要性能参数。由于漏检的存在,可能造成主次级用户业务之间的碰撞,从而引起用户业务的中断或阻塞;另一方面,由于虚警,认知用户将放弃接入可用的空闲频段,从而降低了频谱资源的利用率,无论哪种情形都将导致系统的QoS性能降低。通过将认知网络建模成一个二维马氏链,推导了系统的主要QoS参数。结果表明,尽管误检的存在,认知网络仍能显著提高频谱资源利用率;而主用户的QoS需求也可以通过控制认知业务的接入量来得到保证。     

RAC: Range Adaptive Cognitive Radio Networks

In recent years, cognitive radio has received a great attention due to tremendous potential to improve the utilization of the radio spectrum by efficiently reusing and sharing the licensed spectrum bands, as long as the interference power inflicted on the primary users of the band remains below a predefined threshold level. Cognitive radio allows the secondary users in the cognitive radio network to access the licensed spectrum of the primary users opportunistically. In this paper, an autonomous distributed adaptive transmission range control scheme for cognitive radio networks which is called the RAC is proposed. The RAC considers the QoS requirements of both the primary and the secondary users simultaneously. The cognitive user's maximization of its achievable throughput without interfering the primary user by adapting transmission range of the secondary users dynamically is the key feature of the RAC. One of the advantages of using the proposed scheme is its implementation simplicity. The RAC is compared to other cognitive radio schemes in a simulation environment by using ns2. Simulations indicate that, the RAC can well fit into the mobile cognitive radio ad hoc networks and improve the network performance. Having compared to the other schemes utilizing contemporary cognitive radio technology, the RAC provides better adaptability to the environment and maximizes throughput and minimizes data delivery latency.     

一种解决认知无线电网络模仿主用户攻击问题的方案

针对认知无线电网络中出现的模仿主用户攻击问题,提出一种基于HASH匹配技术的解决方案.当主用户网络工作时,主用户基站在要传输的数据上附加用于HASH计算的原始数据,然后将它们发送出去,认知用户先对接收到的那些原始数据做HASH计算,然后将计算结果同预先保留的HASH值相比较.如果匹配成功,则证明有主用户出现.方案充分利用HASH函数计算速度快的特点,保证认知用户及时切换频谱,避免干扰主用户正常工作,利用HASH函数单向不可逆的特点保证了方案的安全性.给出了具体的设计方案.通过与相关方案比较,该方案具有安全、高效、可行的特点,能有效解决认知用户网络中出现的模仿主用户攻击问题.     

认知传感网络的信能无线传输优化

针对目前无线传感网络频谱资源匮乏、能源供给不足等问题,本文构建了一种新型的认知多播无线传感网络,并研究适用于该网络的信能协同传输问题。以网络中所有次级用户收集到的和能量为优化目标,结合多播技术,在次用户对主用户的干扰、次用户的信干噪比、次级发射器的发射功率的约束下,构建了一种非线性非凸优化问题。针对该优化问题,提出一种基于半正定松弛的算法,从而延长网络的生存周期;并在此基础上提出一种基于序贯参数凸逼近技术的优化算法以降低复杂度。仿真结果表明,本文所提的算法有效提高了次用户能量收集的性能。     

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.     

认知无线电网络中感知时间与功率分配的优化

针对多协作用户多信道的情况,讨论了当信道增益固定时,各子信道之间检测时间、总检测时间与传输时间,以及各子信道之间功率分配的问题。区别于以往的单独优化算法,提出了各参数的联合优化算法。以信道容量为目标函数,给出了最优的时间和功率分配算法。实验结果表明,提出的算法能够实现频谱接入并且极大地提高了次用户系统的总信道容量。表明功率分配与信道上主用户占用的概率有关,而时间分配则与信道上主用户接收信噪比以及传输时自身的信噪比有关。在多认知用户网络中,参与合作的用户越多,接收与传输信噪比越高,次用户系统的总信道容量越大。对于认知无线电网络,还考虑了整体的实现。     

Operating point selection for primary and secondary users in cognitive radio networks

This paper addresses the problem of opportunistic access of secondary users to licensed spectrum in cognitive radio networks. In order to avoid interference to the licensed primary users, efficient spectrum detection methods need to be developed. For this purpose, in recent years several sensing techniques have been proposed to monitor and regulate the spectrum access to the shared spectrum resources. However, spectrum sensing may be affected by errors in the form of missed-detections (i.e., an occupied spectrum is erroneously detected as free) or false-alarms (i.e., a free spectrum is erroneously detected as occupied). These two magnitudes pose a tradeoff on the design of the spectrum sensing mechanisms meaning that low missed-detection can only be achieved at the expense of high false-alarm and vice versa. Thus, the network designers should adaptively tune the sensing techniques such that the highest perceived Quality of Service (QoS) is achieved by both primary and secondary users. In this paper, a framework is introduced for determining the sensing operating points. Also the definition of Grade-of-Service (GoS) metrics is adopted to the case of primary/secondary users spectrum sharing. It is shown that the operating points of the sensing mechanisms can be easily adjusted according to the current traffic load of both primary and secondary users so that the perceived GoS is maximized. In addition, the Erlang Capacity of the spectrum sharing system for both primary and secondary users is also evaluated considering the effects of erroneous sensing.