Delay alignment modulation (DAM) is a promising technology to achieve ISI-free wideband communication, by leveraging delay compensation and path-based beamforming, rather than the conventional channel equalization or multi-carrier transmission. In particular, when there exist a few strong time-dispersive channel paths, DAM can effectively align different propagation delays and achieve their constructive superposition, thus especially appealing for intelligent reflecting surfaces (IRSs)-aided communications with controllable multi-paths. In this paper, we apply DAM to multi-IRS aided wideband communication and study its practical design and achievable performance. We first provide an asymptotic analysis showing that when the number of base station (BS) antennas is much larger than that of IRSs, an ISI-free channel can be established with appropriate delay pre-compensation and the simple path-based MRT beamforming. We then consider the general system setup and study the problem of joint path-based beamforming and phase shifts design for DAM transmission, by considering the three classical beamforming techniques on a per-path basis, namely the low-complexity path-based MRT beamforming, the path-based ZF beamforming for ISI-free DAM communication, and the optimal path-based MMSE beamforming. As a comparison, OFDM-based multi-IRS aided communication is considered. Simulation results demonstrate that DAM outperforms OFDM in terms of spectral efficiency, BER, and PAPR.

翻译：延迟对齐调制（DAM）是一种有前景的技术，通过利用延迟补偿和基于路径的波束赋形，而非传统的信道均衡或多载波传输，实现无符号间干扰（ISI）的宽带通信。特别地，当存在少数强时延色散信道路径时，DAM能有效对齐不同传播延迟并实现其建设性叠加，因此对于具有可控多径的智能反射面（IRS）辅助通信尤为吸引人。本文首次将DAM应用于多IRS辅助的宽带通信，研究其实用设计与可达性能。首先，我们进行渐近分析，表明当基站（BS）天线数远大于IRS数时，通过适当的延迟预补偿和简单的基于路径的MRT波束赋形，可以建立无ISI信道。随后，考虑通用系统设置，研究基于路径的联合波束赋形与相位偏移设计问题以实现DAM传输，分别考虑三种经典的逐路径波束赋形技术：低复杂度的基于路径的MRT波束赋形、用于无ISI DAM通信的基于路径的ZF波束赋形，以及最优的基于路径的MMSE波束赋形。作为对比，还考虑了基于OFDM的多IRS辅助通信。仿真结果表明，DAM在频谱效率、误码率（BER）和峰均功率比（PAPR）方面均优于OFDM。