基于方向调制的安全精准无线传输理论与方法研究

To address the secure problem of the conventional directional modulation exists , we will propose the new concept of secure precise wireless transmission. In this project, we focus on the investigation of secure precise wireless communications including its basic theory and crucial technologies: Firstly, system model is established and the corresponding expressions for secure sum-capacity and symbol error rate (SER) etc are derived, which will lay an information theoretical basis for the design of the link transmission; Secondly, in the presence of artificial noise (AN)/interference, the high-performance channel estimator and optimal pilot pattern are developed, and the sum-variance of channel estimation errors is minimized by quadratic optimization; in the presence of measurement errors on direction and distance of desired and undesired receivers, the ideas of leakage and mutual information will be adopted to construct the robust secure beamforming vectors for useful confidential messages, projection matrix for AN, and main-beam-aligning between transmit and receive antenna arrays, which can approximately achieve the secure sum-capacity, to precisely interfere with those illegitimate desired users; when the number of transmit antennas tends to medium or large-scale, the asymptotic secure sum-rate, and SER are observed and derived, the low-complexity beamforming and beam-aligning algorithms are devised, and the efficient ways to reduce the accumulation of AN at desired receiver, due to multi-path, are sought. Our project covers the study of secure sum-capacity, link transmission, and key patents of secure precise wireless systems, and will offer a theory support, some key techniques, and a novel solution for the future secure wireless networks of our nation. The proposed secure precise wireless transmission will work with traditional cryptography together to provide a two-fold protection for future wireless networks, which is very important for personal privacy and security of national wireless network in the future.

针对传统方向调制存在安全隐患，提出基于方向调制的安全精准无线传输新思路：建立系统模型并推导对应安全和容量、平均误符号率等解析公式，为链路传输提供信息论基础；存在人为噪声场景下，发展高性能信道估计器和最优训练图样，通过二次优化最小化估计器的和方差；考虑方位角与距离估计存在误差，拟采用条件泄露与互信息量等概念，来构造可达安全和容量的稳健有用隐私信息波束成型向量、人为噪声投影矩阵以及波束对齐算法，从而精准干扰非法窃听用户，实现安全精准传输；当发射天线数趋近中大规模时，推导渐进安全和速率、误符号率等，设计低复杂度波束成型与对齐方法，以及探寻如何有效减少多径汇聚人为噪声效应的手段。本项目涉及安全精准无线通信容量、链路传输与核心专利，为未来无线网络安全提供理论支撑、关键技术和全新的解决方案，与传统的密码学相结合将为未来无线网络安全构筑双重屏障，对于未来保护个人隐私与保障国家无线信息网络安全至关重要。

在方向调制（Directional modulation，DM）安全无线传输系统的实际应用中，考虑到存在期望用户和窃听用户信号的到达角（Direction of arrival，DOA）误差，提出了一种自适应稳健波束成形算法。在此基础上提出了一种最大化安全速率功率分配策略，以优化有用信号和人工噪声的功率分配，进而推导出其最优功率分配策略的闭合表达式。针对传统方向调制系统中发射波束仅具有角度依赖性的缺点而导致的安全隐患问题，提出了精准安全传输的新思路：通过随机子载波选择、方向调制和相位对齐三项关键技术，使发射波束形成方向角-距离二维依赖性。并推导了采用正交空间投影方法的信干噪比和安全速率理论表达式，给出窃听区域的SINR上界。同时验证了在发射天线趋于中大规模或中低信噪比区域时，推导的平均安全速率的理论表达式与实际蒙特卡罗仿真结果保持一致。针对进一步降低窃听者截获隐私信息的能力，构建了安全的精准干扰与通信一体化框架，并提出了最小发送功率（Min-TP）和最小正则化发送功率（Min-RTP）两种安全的波束成形算法，从而在窃听用户和期望用户处分别形成能量主峰，有效干扰窃听用户，同时提高期望用户安全速率。此外，还引入无自干扰的无源智能反射表面（IRS），从而实现两路隐私信息同时传输到合法用户。并提出了两种交替迭代算法，以联合设计发射波束成形和IRS相移矩阵：基于最大化安全速率的通用交替迭代算法和基于最大化安全速率的零空间投影算法。由于IRS的存在，克服了DM系统在白高斯信道的传输局限性，使系统在传输双路隐私信息的情况下可达到近一倍的安全性能增益。本项目组所提出的波束成形、子载波选择、功率分配、相位对齐等算法以及安全性能分析，可为安全精准无线传输技术提供理论基础及新思路、新途径，可应用于未来的移动通信、物联网、毫米波通信、无人机等无线接入网络，以实现对隐私信息的强大保护。