毫米波无线通信物理层安全传输技术研究

毫米波无线通信物理层安全传输技术研究摘要安全性能是无线通信系统的一项重要指标。传统的加密安全通信技术是在系统上层先对信息进行加密处理，然后通过无线信道传输到目标用户。但由于无线信号的广播传输特性，窃听者很容易窃听到加密后的无线信号并采用高性能的计算机进行破解。因此，传统的加密安全通信技术仍然存在安全威胁。物理层安全技术是利用信道特征实现安全无线通信，无需在系统上层对信息进行加密。由于低频段频谱资源枯竭，新一代无线通信系统为满足更宽带宽和更高速率需求，载波频率朝着更高频的毫米波频段发展已成必然。通信频段的升高，引起了信道特性的变化。毫米波路径损耗大、反射能力强、衍射能力弱的独特信道特性使得无线通信方式从单天线向大规模天线阵波束成形转变，产生物理层安全通信研究的新挑战。由于毫米波波束的定向性能高，窃听者只有在旁瓣采用灵敏度高的接收设备或追踪波束主瓣才能窃听信号。研究解决旁瓣区域敏感窃听问题和波束主瓣窃听问题对提升毫米波波束成形传输系统的物理层安全性能意义重大。为此，本文针对传统波束旁瓣区域的敏感窃听难题和波束主瓣窃听难题，通过开拓相控天线阵列的幅度、频率和相位自由度，提出可编程幅度权重定向角度波束成形、旋转角度波束成形和定区域波束形成三种物理层安全传输技术方案。论文的主要研究工作和所提出的创新性总结如下：1. 旁瓣随机化的定向角度波束成形物理层安全传输技术。为解决定向波束旁瓣方向的敏感窃听难题，将波束旁瓣泄漏信号转化为人工噪声，提出了用可编程幅度权重相控阵结构实现反转幅度天线子集和最优幅度权重子集的定向波束旁瓣随机化波束成形技术方案。推导了波束形成系数和接收信号的数学统计特征定理，得到旁瓣随机化信号的近似高斯分布特征。研究人工噪声功率最大化的天线子集设计优化方案，可提升安全速率达33%。设计模拟退火粒子群优化算法构建优质天线子集矢量码本，波束旁瓣方向的随机化幅度峰值可降低21.12dB。2. 旋转角度波束成形物理层安全传输技术。为解决波束主瓣方向的窃听难题，通过开拓多频相控阵列的频率自由度，提出了角度距离双参数控制的可旋转角度波束成形物理层安全传输技术。提出了波束旋转定理，公式化了波束旋转角度与频率偏移增量的关系表达式。采用波束零旁瓣旋转技术避免已知位置信息的窃听。采用波束动态旋转技术降低旁瓣平均增益，避免未知位置信息的窃听者捕捉到波束主瓣实施窃听。3. 定区域传输波束成形物理层安全传输技术。为解决波束主瓣传输路径上的物理层安全失效难题，提出控制多频相控子阵列的频率偏移增量矢量实现子波束在目标区域有效叠加和在目标区域外相互抵消的定区域波束成形技术。设计人群搜索算法和块坐标下沉线性逼近算法，分别解决未知窃听位置信息和已知窃听位置信息的多频相控子阵列频率偏移增量矢量选择的NP-Hard问题。分析了天线子阵列的划分方案、最大频率偏移增量设置范围与安全速率的关系。仿真表明，定区域波束成形技术在安全中断概率比传统波束成形的安全中断概率可低205倍。综上所述，论文针对毫米波波束成形无线通信存在的物理层安全传输挑战难题，提出了三种波束成形技术的物理层安全传输方案，解决了波束旁瓣区域敏感窃听难题和波束主瓣上的零安全速率难题。系统的仿真结果验证了论文所提技术方案的有效性。关键字：物理层安全；毫米波；相控阵列；波束成形；安全速率IXABSTRACTResearch of Physical Layer Security Transmission Technique for Millimeter Wave Wireless Communications AbstractSecurity performance is an important index in wireless communication systems. The traditional encryption secure communication technology is to encrypt the information in the upper layer of the system and then transmit it to the target user through the wireless channel. However, due to the broadcast feature of wireless signal, eavesdropper can easily eavesdrop the encrypted wireless signals and use high performance computer to crack. Thus, the tradition method still has security threats. Physical layer security (PLS) technology is a secure communication technology that can replace the traditional encryption technology. It utilizes the characteristics of the channel to achieve secure wireless communication without encryption in the upper layerDue to the exhaustion of low-band spectrum resources, the development of carrier frequencies in new generation wireless communication system towards higher frequency millimeter wave (mmWave) has become inevitable for wider bandwidth and higher rate. The increase of communication frequency band has caused changes of channel characteristics. The unique mmWave channel characteristics of larger path loss, strong reflection and weak diffraction make the wireless communication method change from single antenna to large-scale antenna array beamforming. which brings new challenges to the PLS communication research. Due to the high directional performance of mmWave beams, eavesdroppers can only eavesdrop the signals by using high sensitivity receiving devices in the side lobe or tracking the mainlobe. Thus, studying and solving the sensitive eavesdropping problem in the sidelobe area and eavesdropping problem in the mainlobe is of great significance to improve the PLS performance of mmWave beamforming transmission system.Motived by these, aiming at the problems of sensitive eavesdropping in the sidelobe regions and the mainlobe eavesdropping, this paper proposes the three PLS transmission schemes, which are programmable amplitude weight fixed angle beamforming (FAB), rotating angle beamforming (RAB) and fixed region beamforming (FRB), by exploiting the amplitude, frequency and phase degrees of freedoms (DOFs) of the phased antenna array. The main research works and the contributions are summarized as follows. 1. Sidelobe randomized FAB PLS secure transmission technology. In order to solve the problem of sensitive eavesdropping in the sidelobe directions of FAB and convert the beam sidelobe leakage signal into artificial noise, the sidelobe randomized technologies of inverted amplitude antenna subset and optimal amplitude weight subset based a programmable amplitude weighted phased array structure are proposed. The mathematical statistical characteristic theorems of beamforming coefficient and the received signal are derived, and the approximate Gaussian distribution characteristic of the sidelobe randomized signal is obtained. The optimal design of the antenna subset for maximizing the power of artificial noise is studied, which can improve the secrecy rate by 33%. A simulated annealing particle swarm optimization algorithm is designed to construct a high-quality antenna subset vector codebook, and the peak value of the randomized amplitude of the sidelobes of the beam can be reduced by 21.12dB. 2. RAB PLS transmission technology. To sovle the eavesdropping problem in the direction of mainlobe, an angular range dual-parameter controlled RAB PLS transmission techn