In this paper, we consider the problem of joint transceiver design for millimeter wave (mmWave)/Terahertz (THz) multi-user MIMO integrated sensing and communication (ISAC) systems. Such a problem is formulated into a nonconvex optimization problem, with the objective of maximizing a weighted sum of communication users' rates and the passive radar's signal-to-clutter-and-noise-ratio (SCNR). By exploring a low-dimensional subspace property of the optimal precoder, a low-complexity block-coordinate-descent (BCD)-based algorithm is proposed. Our analysis reveals that the hybrid analog/digital beamforming structure can attain the same performance as that of a fully digital precoder, provided that the number of radio frequency (RF) chains is no less than the number of resolvable signal paths. Also, through expressing the precoder as a sum of a communication-precoder and a sensing-precoder, we develop an analytical solution to the joint transceiver design problem by generalizing the idea of block-diagonalization (BD) to the ISAC system. Simulation results show that with a proper tradeoff parameter, the proposed methods can achieve a decent compromise between communication and sensing, where the performance of each communication/sensing task experiences only a mild performance loss as compared with the performance attained by optimizing exclusively for a single task.

翻译：本文研究了毫米波/太赫兹多用户MIMO通信感知一体化系统中联合收发机设计问题。该问题被建模为一个非凸优化问题，其目标为最大化通信用户速率与无源雷达信杂噪比的加权和。通过利用最优预编码器的低维子空间性质，本文提出了一种低复杂度的基于块坐标下降的算法。分析表明，当射频链数量不小于可分辨信号路径数量时，混合模拟/数字波束赋形结构可达到与全数字预编码器相同的性能。此外，通过将预编码器表示为通信预编码器与感知预编码器之和，我们将块对角化思想推广至ISAC系统，从而推导出联合收发机设计问题的解析解。仿真结果表明，在适当的权衡参数下，所提方法可在通信与感知之间实现良好折中，与针对单一任务优化所获得的性能相比，每个通信/感知任务的性能仅遭受轻微损失。