  This paper proposes a novel broadband transmission technology, termed delay
alignment modulation (DAM), which enables the low-complexity equalization-free
single-carrier communication, yet without suffering from inter-symbol
interference (ISI). The key idea of DAM is to deliberately introduce
appropriate delays for information-bearing symbols at the transmitter side, so
that after propagating over the time-dispersive channel, all multi-path signal
components will arrive at the receiver simultaneously and constructively. We
first show that by applying DAM for the basic multiple-input single-output
(MISO) communication system, an ISI-free additive white Gaussian noise (AWGN)
system can be obtained with the simple zero-forcing (ZF) beamforming.
Furthermore, the more general DAM scheme is studied with the ISI-maximal-ratio
transmission (MRT) and the ISI-minimum mean-square error (MMSE) beamforming.
Simulation results are provided to show that when the channel is sparse and/or
the antenna dimension is large, DAM not only resolves the notorious practical
issues suffered by orthogonal frequency-division multiplexing (OFDM) such as
high peak-to-average-power ratio (PAPR), severe out-of-band (OOB) emission, and
vulnerability to carrier frequency offset (CFO), with low complexity, but also
achieves higher spectral efficiency due to the saving of guard interval
overhead.
