【作者】 王文忠；

【导师】 周正；

【作者基本信息】 北京邮电大学 ， 电路与系统， 2008， 博士

【摘要】 频谱感知是实现认知无线电网络应用的首要的关键技术之一,近年来受到人们广泛的关注而成为当前研究的热点。本文选题来源于国家自然科学基金等项目,旨在提高认知无线电网络频谱感知的可靠性和有效性,具有重要的理论意义和应用前景。本文主要从多个用户的联合频谱感知的角度出发,在无线通信环境下,通过分析信号衰落、阴影效应以及隐性终端等问题对频谱感知性能造成的影响,探索提高认知无线电网络频谱感知的整体性能。本文的主要工作及创新点如下:针对认知无线电网络在不同的检测融合结构以及在相同信噪比和不同信噪比的情况下,频谱感知性能的差异讨论并解决频谱感知融合后性能下降的问题,本文提出了一种基于信噪比划分等级的等级频谱感知融合的算法。其主要思想是通过对频谱感知节点按信噪比的大小进行分组,利用相同信噪比的情况下,检测融合的并行结构可以获得最佳的检测性能的优点,及在不同信噪比的情况下,检测融合的串行结构能够保持高信噪比节点的检测性能的特点,能保证在不同情况下,获得频谱感知信息的最佳或准最佳融合。仿真结果表明这种方式简便易行,计算复杂度低,能够在系统级上达到提高检测概率、降低虚警概率的目的。针对具体的检测融合的判决规则,目前的研究结果只是考虑简单地采用“与规则”、“或规则”等判决规则,没有考虑检测概率、虚警概率及频谱感知的节点数量对检测融合性能的影响。本文通过对融合判决规则进行的深入分析,给出了不同的检测融合规则的性质及其适用条件。利用这些适用条件把分布式检测融合的理论运用到本地频谱感知技术中,可得到低复杂度的提高频谱感知检测性能的方法。仿真结果表明,这种方法能够抵抗由于缺少先验信息而导致的本地频谱感知的性能下降。针对在通信带宽受限情况下如何提高频谱感知的检测性能的问题,本文提出了一种审核检测融合判决规则的算法,即增加了对未发送检测报告的节点的状态进行考虑的三元判决融合方式。与只考虑频谱感知信息“0”、“1”状态的常规的二元检测融合规则相比,在不增加通信量的基础上,审核检测融合判决规则能获得更好的检测性能,仿真结果表明即使在节点数很少的情况下,频谱感知的检测性能的也有显著的提高。本文还对分布式检测融合在认知无线电网络安全方面的应用进行了探索,提出了一种将检测融合与异常点检测相结合的方法,把检测融合规则与异常点检测相结合,作为抵御认知无线电网络中出现故障节点或恶意节点的手段。通过计算机仿真可以看出,这种方式可以增加在恶劣环境下认知无线电频谱感知的鲁棒性,本文的研究结果也为此领域的研究开辟出一个新的研究方向。更多还原

【Abstract】 Spectrum Sensing is the key technology for Cognitive Radio (CR) because it is crucial for the success of cognitive radio and it will guarantee service improvement to unlicensed users and avoidance of interference to licensed users. This research is supported by projects like National Science Funds, Beijing Municipal Natural Science Fund etc, and attempts to make a contribution to the theory and application of spectrum sensing for the system cognitive radio network.This dissertation mainly concentrate on the increase of reliability and efficience of cooperative spectrum sensing by multiple cognitive radio users, and studies the fading, shadowing effects and the hidden terminal problem on the performance of spectrum sensing. The main contributions and creative algorithms which are developed in this dissertation are listed in the following:We make an exploration into the spectrum sensing from the view of distributed detection and attempt to increase the detection probability and to lower false alarm probability for the whole cognitive radio network and examine the detection performance of spectrum sensing under different network configuration. When the spectrum sensing nodes are similar with each other i.e. their observations are from same probability distribution, the optimum fusion network is in parallel configuration. However the detection performance of parallel configuration decreases greatly when the detection nodes are dissimilar due to fading and shadowing of radio channels especially when most of them are at low SNR states its performance is inferior to that of high SNR node. The hierarchy fusion scheme we proposed in this paper incorporates both parallel and serial configuration and classifies detection nodes into different groups by their SNR levels. The receiver operation characteristic (ROC) of hierarchy fusion rule shows that the detection efficiency and reliability can be increased no matter the detection nodes are similar or dissimilar.We also analyze fusion rules and deduce their properties and conditions because at present only "OR" rule and "AND" rule are considered and the influence of the node number, the false alarm and detection probabilities are disregarded for most research work. Actually these properties and conditions can be used to improve the detection performance as a low complexity method and the uncertainty of spectrum sensing due to the lack of aprior knowledge of licensed signals can be lessened when proper fusion rule is chosen.When communication is under bandwidth constraint, spectrum sensing sensor nodes normally only send one bit report to fusion center and censoring detection method is employed by sensor nodes. However only conventional fusion rules are considered and the "No decision" information by censoring sensor nodes is disregarded by recent research work. The censoring fusion scheme we proposed incorporates "No decision" message for decision fusion can significantly outdo conventional fusion rules on the improvement of the detection performance of spectrum sensing without traffic increase. By analytical results and numerical computation, we demonstrate that the censoring fusion scheme can make great improvement on the detection performance of spectrum sensing even thoug the node number is small.At last part we attempt to apply decision fusion rules into the security issue of spectrum sensing and propose a decision fusion scheme that combines with the outlier detection method. This scheme can improve the robustness of spectrum sensing when some sensing nodes are malfunctioned or malicious and make a new attempt to CR security issue from distributive detection aspect.更多还原