Double-Side Delay Alignment Modulation for Multi-User Millimeter Wave and TeraHertz Communications

TL;DR

This paper introduces a double-side delay alignment modulation (DAM) technique for multi-user millimeter wave and terahertz communications, improving spectral efficiency and reducing PAPR compared to OFDM, especially with large antenna arrays.

Contribution

It extends DAM to a double-side approach, analyzes delay constraints, and proposes low-complexity beamforming strategies for multi-user systems.

Findings

Double-side DAM is effective with large antenna arrays.

Single-side DAM suffices when antennas are sufficiently large.

Multi-user BS-side DAM outperforms OFDM in spectral efficiency and PAPR.

Abstract

Delay alignment modulation (DAM) is an innovative broadband modulation technique well suited for millimeter wave (mmWave) and terahertz (THz) massive multiple-input multiple-output (MIMO) communication systems. Leveraging the high spatial resolution and sparsity of multi-path channels, DAM mitigates inter-symbol interference (ISI) effectively, by aligning all multi-path components through a combination of delay pre/post-compensation and path-based beamforming. As such, ISI is eliminated while preserving multi-path power gains. In this paper, we explore multi-user double-side DAM with both delay pre-compensation at the transmitter and post-compensation at the receiver, contrasting with prior one-side DAM that primarily focuses on delay pre-compensation only. Firstly, we reveal the constraint for the introduced delays and the delay pre/post-compensation vectors tailored for multi-user double-side DAM, given a specific number of delay pre/post-compensations. Furthermore, we show that as long as the number of base station (BS)/user equipment (UE) antennas is sufficiently large, single-side DAM, where delay compensation is only performed at the BS/UE, is preferred than double-side DAM since the former results in less ISI to be spatially eliminated. Next, we propose two low-complexity path-based beamforming strategies based on the eigen-beamforming transmission and ISI-zero forcing (ZF) principles, respectively, based on which the achievable sum rates are studied. Simulation results verify that with sufficiently large BS/UE antennas, single-side DAM is sufficient. Furthermore, compared to the benchmark scheme of orthogonal frequency division multiplexing (OFDM), multi-user BS-side DAM achieves higher spectral efficiency and/or lower peak-to-average power ratio (PAPR).