For integrated sensing and communication (ISAC) systems, the channel information essential for communication and sensing tasks fluctuates across different timescales. Specifically, wireless sensing primarily focuses on acquiring path state information (PSI) (e.g., delay, angle, and Doppler) of individual multi-path components to sense the environment, which usually evolves much more slowly than the composite channel state information (CSI) required for communications. Typically, the CSI is approximately unchanged during the channel coherence time, which characterizes the statistical properties of wireless communication channels. However, this concept is less appropriate for describing that for wireless sensing. To this end, in this paper, we introduce a new timescale to study the variation of the PSI from a channel geometric perspective, termed path invariant time, during which the PSI largely remains constant. Our analysis indicates that the path invariant time considerably exceeds the channel coherence time. Thus, capitalizing on these dual timescales of the wireless channel, in this paper, we propose a novel ISAC framework exploiting the recently proposed delay-Doppler alignment modulation (DDAM) technique. Different from most existing studies on DDAM that assume the availability of perfect PSI, in this work, we propose a novel algorithm, termed as adaptive simultaneously orthogonal matching pursuit with support refinement (ASOMP-SR), for joint environment sensing and PSI estimation. We also analyze the performance of DDAM with imperfectly sensed PSI.Simulation results unveil that the proposed DDAM-based ISAC can achieve superior spectral efficiency and a reduced peak-to-average power ratio (PAPR) compared to standard orthogonal frequency division multiplexing (OFDM).

翻译：针对集成感知与通信（ISAC）系统而言，通信与感知任务所需的信道信息在不同时间尺度上存在波动。具体而言，无线感知主要关注获取单个多径分量的路径状态信息（PSI）（如时延、角度和多普勒）以感知环境，这类信息通常比通信所需的复合信道状态信息（CSI）演化得更为缓慢。通常，CSI在信道相干时间内近似不变，该时间尺度刻画了无线通信信道的统计特性，但这一概念并不完全适用于描述无线感知特性。为此，本文从信道几何视角引入一种研究PSI变化的新时间尺度——路径不变时间，在此期间PSI基本保持恒定。分析表明，路径不变时间显著长于信道相干时间。因此，基于无线信道的双时间尺度特性，本文利用最新提出的延迟-多普勒对齐调制（DDAM）技术，构建了一种新型ISAC框架。与现有大多数假设完美PSI可用的DDAM研究不同，本文提出一种名为"基于支撑集优化的自适应同步正交匹配追踪（ASOMP-SR）"的新算法，用于联合环境感知与PSI估计。同时，本文分析了基于非完美感知PSI的DDAM性能。仿真结果表明，与标准正交频分复用（OFDM）相比，所提出的DDAM-ISAC框架能够实现更高的频谱效率并降低峰均功率比（PAPR）。