This paper introduces delay-alignment modulation (DAM) for secure integrated sensing and communication (ISAC). Due to the broadcast nature of multi-user downlinks, communications are vulnerable to eavesdropping. DAM applies controlled per-path symbol delays at the transmitter to coherently align the multipath components at the intended user, enhancing the received signal power, while simultaneously creating delay misalignment at the eavesdropper (Eve). To mitigate sensing degradation caused by multipath propagation, we propose a two-stage protocol that first estimates the angle and then the delay of the line-of-sight (LoS) path after suppressing multipath interference. We derive the secrecy spectral efficiency (SSE) and the Cramer-Rao (CRB) of the target delay. Finally, we develop a path-based zero-forcing (ZF) precoding framework and formulate a max-min SSE design under CRB and power constraints. Simulation results show DAM significantly outperforms the strongest-path (SP) benchmark in terms of SSE, while meeting sensing requirements, since intentional delay alignment at legitimate users degrades reception at Eve.

翻译：本文针对安全集成感知与通信系统提出时延对齐调制技术。由于多用户下行链路的广播特性，通信过程易受窃听威胁。DAM在发射端对每条路径施加可控的符号时延，使多径分量在目标用户处实现相干对齐，从而提升接收信号功率；同时使窃听者处的多径分量产生时延失配。为缓解多径传播导致的感知性能退化，我们提出两阶段处理协议：首先在抑制多径干扰后估计视距路径角度，继而估计其时延参数。我们推导了保密频谱效率的解析表达式及目标时延估计的克拉美-罗下界。基于此，我们建立了基于路径的迫零预编码框架，并在CRB与功率约束下构建了最大-最小SSE优化问题。仿真结果表明：由于在合法用户端实现的时延对齐会劣化窃听者接收性能，DAM在满足感知需求的同时，其SSE性能显著优于最强路径基准方案。