[论文解读] Intelligent Reflecting Surface Assisted Integrated Sensing and Communications for mmWave Channels

Zhengyu Zhu, Zheng Li+5 more|arXiv (Cornell University)|Jan 5, 2022

Advanced Wireless Communication Technologies被引用 5

一句话总结

本文提出了一种智能反射面（IRS）辅助的太赫兹波（mmWave）频段集成感知与通信（ISAC）系统，通过联合优化雷达信号协方差、通信波束成形和IRS相位移，最大化和速率的同时平衡感知与通信性能。提出了一种闭式解以及结合二次变换、主化最小化和流形优化的交替优化方法，结果表明IRS能显著提升ISAC性能，且计算复杂度较低。

ABSTRACT

This paper proposes an intelligent reflecting surface (IRS) assisted integrated sensing and communication (ISAC) system operating at the millimeter-wave (mmWave) band. Specifically, the ISAC system combines communication and radar operations and performs, detecting and communicating simultaneously with multiple targets and users. The IRS dynamically controls the amplitude or phase of the radio signal via reflecting elements to reconfigure the radio propagation environment and enhance the transmission rate of the ISAC system. By jointly designing the radar signal covariance (RSC) matrix, the beamforming vector of the communication system, and the IRS phase shift, the ISAC system transmission rate can be improved while matching the desired waveform for radar. The problem is non-convex due to multivariate coupling, and thus we decompose it into two separate subproblems. First, a closed-form solution of the RSC matrix is derived from the desired radar waveform. Next, the quadratic transformation (QT) technique is applied to the subproblem, and then alternating optimization (AO) is employed to determine the communication beamforming vector and the IRS phase shift. For computing the IRS phase shift, we adopt both the majorization minimization (MM) and the manifold optimization (MO). Also, we derive a closed-form solution for the formulated problem, effectively decreasing computational complexity. Furthermore, a trade-off factor is introduced to balance the performance of communication and sensing. Finally, the simulations verify the effectiveness of the algorithm and demonstrate that the IRS can improve the performance of the ISAC system.

研究动机与目标

• 为解决B5G/6G mmWave ISAC系统中的频谱稀缺与高硬件成本问题。
• 通过低成本IRS重构无线传播环境，提升mmWave频段的ISAC性能。
• 联合优化雷达信号协方差矩阵、通信波束成形与IRS相位移，以最大化和速率。
• 通过系统加权因子平衡通信与雷达性能之间的权衡。
• 通过闭式解与高效优化技术降低计算复杂度。

提出的方法

• 提出了一种联合优化框架，用于mmWave ISAC系统中的雷达信号协方差矩阵（RSC）、通信波束成形向量与IRS相位移。
• 基于期望雷达波形推导出RSC矩阵的闭式解，以确保波形匹配。
• 应用二次变换（QT）将非凸问题重构为可处理的子问题。
• 采用交替优化（AO）迭代求解波束成形与IRS相位移。
• 利用主化最小化（MM）与流形优化（MO）高效计算IRS相位移。
• 引入权衡参数λ，以平衡通信和速率与雷达检测性能。

实验结果

研究问题

• RQ1 如何利用IRS在保持雷达性能的同时提升mmWave ISAC系统的和速率？
• RQ2 在IRS辅助的ISAC系统中，雷达信号协方差、波束成形与IRS相位移的最优联合设计是什么？
• RQ3 权衡参数λ如何影响通信与感知性能之间的平衡？
• RQ4 IRS相位移分辨率（B位）对系统和速率及与连续相位的性能差距有何影响？
• RQ5 IRS反射单元数与通信天线数如何影响系统性能？

主要发现

• 所提出的IRS辅助ISAC系统在IRS反射单元较多时，实现了显著的和速率增益。
• 增加IRS反射单元数在提升和速率方面比增加通信天线数更有效。
• 当系统加权因子λ较高（偏向通信）时，雷达检测概率降低，尤其在低信噪比（SNR）下更为明显。
• 当雷达SNR超过13 dB时，检测概率保持较高水平，无论λ取值如何，表明对权衡参数的敏感性降低。
• 随着相位分辨率B增加，连续相位与离散相位之间的性能差距减小，B=3位时已足够实现近似最优性能。
• 闭式解与基于MM/MO的优化方法显著降低了计算复杂度，同时保持了高性能。