波动双径衰落信道下的圆阵方向调制方法

为了实现对三维空间中任意期望方向的物理层安全通信，提出了一种基于均匀圆阵的方向调制发射机系统模型，使用迫零波束形成发射有用信号的同时用零空间映射法发射随机的人工噪声干扰非期望方向.针对当前对毫米波信号小尺度衰落刻画较好的波动双径（fluctuating two-ray，FTR）衰落信道，推导了本文模型的平均安全容量（average secrecy capacity，ASC）下界、安全中断概率（secrecy outage probability，SOP）上界的闭合表达式，对比了系统安全性能关于信噪比的变化曲线.仿真结果表明，阵元数为64，信噪比为10 dB，圆阵方向调制在期望方向可以无失真地恢复信号，非期望方向误差向量幅度（error vector magnitude，EVM）高达100%，误比特率高于40%.本文方法能在三维空间实现无需密钥的定向安全传输，提高信噪比可改善其在FTR衰落信道下的安全性能.

Circular array directional modulation over fluctuating two-ray fading channel

To achieve the physical layer security communication towards any desired direction in 3D space, a directional modulation transmitter model based on uniform circular array is proposed. Zero-forcing beamforming and null space projection are used for useful signals and artificial noise (AN) transmission. Closed-form expressions of lower bound for average secrecy capacity(ASC) and upper bound for secrecy outage possibility(SOP) under fluctuating two-ray (FTR) fading channel are derived. Curves of system security performance against signal-to-noise ratio (SNR) are contrasted. Computer simulations show that the proposed directional modulation achieves undistorted modulated signal in desired direction for circular array with 64 elements and SNR with 10 dB, as well as that the error vector magnitudes(EVM) are up to 100% and BERs are higher than 40% in most undesired directions. Our method can realize secure transmission in 3D space without encryption and its security performance can be improved by larger SNR under FTR fading channel.