Delay alignment modulation (DAM) is a novel wideband transmission technique for mmWave massive MIMO systems, which exploits the high spatial resolution and multi-path sparsity to mitigate ISI, without relying on channel equalization or multi-carrier transmission. In particular, DAM leverages the delay pre-compensation and path-based beamforming to effectively align the multi-path components, thus achieving the constructive multi-path combination for eliminating the ISI while preserving the multi-path power gain. Different from the existing works only considering single-user DAM, this paper investigates the DAM technique for multi-user mmWave massive MIMO communication. First, we consider the asymptotic regime when the number of antennas Mt at BS is sufficiently large. It is shown that by employing the simple delay pre-compensation and per-path-based MRT beamforming, the single-carrier DAM is able to perfectly eliminate both ISI and IUI. Next, we consider the general scenario with Mt being finite. In this scenario, we characterize the achievable rate region of the multi-user DAM system by finding its Pareto boundary. Specifically, we formulate a rate-profile-constrained sum rate maximization problem by optimizing the per-path-based beamforming. Furthermore, we present three low-complexity per-path-based beamforming strategies based on the MRT, zero-forcing, and regularized zero-forcing principles, respectively, based on which the achievable sum rates are studied. Finally, we provide simulation results to demonstrate the performance of our proposed strategies as compared to two benchmark schemes based on the strongest-path-based beamforming and the prevalent OFDM, respectively. It is shown that DAM achieves higher spectral efficiency and/or lower peak-to-average-ratio, for systems with high spatial resolution and multi-path diversity.

翻译：延迟对齐调制（DAM）是一种面向毫米波大规模MIMO系统的新型宽带传输技术，它利用高空间分辨率与多径稀疏性来抑制符号间干扰（ISI），无需依赖信道均衡或多载波传输。具体而言，DAM通过延迟预补偿与基于路径的波束成形有效对齐多径分量，从而在保留多径功率增益的同时实现建设性多径组合以消除ISI。不同于现有仅考虑单用户DAM的研究，本文探讨了面向多用户毫米波大规模MIMO通信的DAM技术。首先，我们考虑基站天线数Mt足够大的渐进场景。研究表明，通过采用简单的延迟预补偿与逐路径最大比传输（MRT）波束成形，单载波DAM能够完美消除ISI与用户间干扰（IUI）。其次，我们研究Mt有限的一般场景，通过寻找Pareto边界来刻画多用户DAM系统的可达速率区域。具体而言，我们通过优化逐路径波束成形，构建了速率轮廓约束下的和速率最大化问题。此外，基于MRT、迫零及正则化迫零原则，我们提出了三种低复杂度逐路径波束成形策略，并研究了相应的可达和速率。最后，通过仿真验证了所提策略相对于两种基准方案（基于最强路径波束成形与主流OFDM）的性能优势。结果表明，在高空间分辨率与多径分集系统中，DAM能够实现更高的频谱效率和/或更低的峰均比。