【作者】 刘娟；

【导师】 马丕明；

【作者基本信息】 山东大学 ， 通信与信息系统， 2013， 硕士

【摘要】 鉴于无线媒介的广播特性,其信息传输的安全性一直备受关注。作为对加密技术的一种补充,物理层安全成为一种新的研究方向。在发送信号中添加人工噪声的方式是一种衰落窃听信道下实现保密通信的有效方法。因此,以凸优化理论为数学工具,本文对基于人工噪声的物理层信息安全进行深入研究,重点研究多输入单输出(MISO)系统和认知无线电网络的保密通信的鲁棒性设计。论文的主要工作和创新如下：(1)为实现发射端和合法接收端的保密通信,根据通信系统的物理层特性,引入分布于主信道(发射端和合法接收端之间的信道)零空间内的人工噪声,通过衰落窃听信道(发射端与非法接收端之间的信道),降低非法接收端的信噪比。仿真结果表明,此添加人工噪声的方法在干扰窃听信道的同时不会对主信道造成任何影响,可以实现发射端与合法接收端之间的保密通信,但没有考虑功率分配优化问题。(2)为实现发射功率的合理分配,论文研究一种波束成形矢量和人工噪声的协方差矩阵联合优化的设计方法。假设发射端能获取主信道和窃听信道的完整的信道状态信息(CSI),为保证合法接收端的服务质量,以最小化总发射功率为目标,限制合法接收端信噪比的最小值和非法接收端信噪比的最大值为约束条件,实现发射功率在人工噪声和信息信号之间的合理分配,节省功率资源。仿真结果证明,在实现相同程度的保密通信条件下,添加人工噪声的设计方法比未添加人工噪声的设计方法节省发射功率,也说明人工噪声对于提高系统保密通信性能的作用。(3)针对发射端只获得信道状态信息的均值,信道误差在一定范围内的情况,论文提出了一种基于人工噪声的以优化发射功率为目标的鲁棒性设计方法,对优化问题进行数学建模和数值求解。在求解最优波束成形矢量和人工噪声的协方差矩阵时,CSI存在不确定度,优化问题的约束条件为无限多个,无法求解。论文采用S-procedure定理,将无限个约束条件变换为有限的线性矩阵不等式。仿真结果表明,论文提出的鲁棒性设计方法可提高保密通信系统发射功率的稳定性。(4)考虑到认知无线电技术可以提高频谱资源的利用率,论文研究认知无线电网络环境下的物理层安全问题,对波束成形矢量和人工噪声协方差矩阵进行联合优化。以最大化次用户接收端的信噪比为目标,限制非法接收端的接收信噪比最大值、主用户处的干扰温度(次用户发射信号对主用户接收端产生的干扰功率)及次用户发射功率。在此基础上,以最小化次用户的发射功率为目标,限制次用户的接收信噪比最小值和窃听端接收信噪比的最大值及干扰温度,论文提出了一种新的波束成形矢量和人工噪声协方差矩阵的联合设计方案,并对信道的鲁棒性进行分析。实验结果证明,在认知无线电网络的保密通信中,添加人工噪声可以节省发射功率,提高系统的物理层安全性能。更多还原

【Abstract】 Given the broadcast nature of the wireless medium, the security of data communication has received considerable attentions. As a complement to cryptographic encryption, physical-layer security has become a new research area. Using artificial noise (AN) aided in transmitted signal is one of the efficient methods to guarantee secret communications over fading channels. Hence, the thesis does an in-depth study on the physical-layer security based on AN with convex optimization as math tools. It focuses on the secret communications in multi-input single-output (MISO) systems and cognitive radio networks and their robustness design. The major work and innovations are as follows:To guarantee the secret transmission between transmitter and the legal receiver, artificial noise which lies in the null space of the main channel (channel between transmitter and the legal receiver) according to physical-layer characteristics, to depress the signal-noise-ratio (SNR) at the illegal receiver by crippling its channel. The simulation results prove that the design with AN aided can fade the wire-tap channel while it has no impact on the main channel. And it can guarantee the secret communication between transmitter and legal receiver, but fails to take the optimization of power allocation into consideration.To allocate the transmitted power reasonably, a joint beamforming and artificial noise design are discussed here. On the assumption that transmitter has known perfect channel statement information (CSI) of both the main channel and the eavesdropping channel, to guarantee the legal receiver’s quality of service (QoS), minimizing the transmitted power is set as the object with the maximum SINRs of eavesdroppers and the minimum SINRs of the intended receiver as constraints. The simulation results show that the joint design based on AN can save more transmitting power to achieve the secret communications with the same level,compared with design without AN. Besides, the impact of artificial noise on guaranteeing the secret communication is proved.In allusion to the case that transmitter only knows the mean value and there are channel errors within limits, a robustness design based on AN is proposed, which sets optimizing power as object. Mathematical modeling and solution of the optimization problems are studied. Given the presence of channel uncertainties, the restrictions mentioned before are infinite. To solve the problem efficiently, the constraints are turned into linear matrix inequalities via S-procedure. The simulation results indicate that robustness design can improve the stability of the system.In view of the fact that cognitive radio technique can increase frequency spectrum utilization, the physical-layer security of cognitive radio networks is studied, with joint beamforming and artificial noise design. Firstly, the maximum SNR at SU-Rx is viewed as the objective function, constraining the maximum SNR at eavesdroppers and maximum value of interference temperature (the allowable interference power level at primary receiver) and transmitted power. On that basis above, a new design scheme is proposed. The minimum transmitted power is set as objective function. And the minimum SNR at SU-Rx are maximum value of interference temperature and maximum SNR at eavesdroppers as constraints. Moreover, the robustness designs of the two schemes are given. The simulation results testify the impact of artificial noise on improving the secret communications’ safety performance in cognitive radio networks.更多还原