  Delay alignment modulation (DAM) is a novel wideband communication technique,
which exploits the high spatial resolution and multi-path sparsity of
millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems
to mitigate inter-symbol interference (ISI), without relying on conventional
techniques like channel equalization or multi-carrier transmission. In this
paper, we extend the DAM technique to multi-user mmWave massive MIMO
communication systems. We first provide asymptotic analysis by showing that
when the number of base station (BS) antennas is much larger than the total
number of channel paths, DAM is able to eliminate both ISI and inter-user
interference (IUI) with the simple delay pre-compensation and per-path-based
maximal ratio transmission (MRT) beamforming. We then study the general
multi-user DAM design by considering the three classical transmit beamforming
strategies in a per-path basis, namely MRT, zero-forcing (ZF) and regularized
zero-forcing (RZF). Simulation results demonstrate that multi-user DAM can
significantly outperform the benchmarking single-carrier ISI mitigation
technique that only uses the strongest channel path of each user.
