  Using communications signals for dynamic target sensing is an important
component of integrated sensing and communications (ISAC). In this paper, we
propose to utilize the beam squint effect to realize fast non-cooperative
dynamic target sensing in massive multiple input and multiple output (MIMO)
Terahertz band communications systems. Specifically, we construct a wideband
channel model of the echo signals, and design a beamforming strategy that
controls the range of beam squint by adjusting the values of phase shifters and
true time delay lines. With this design, beams at different subcarriers can be
aligned along different directions in a planned way. Then the received echo
signals at different subcarriers will carry target information in different
directions, based on which the targets' angles can be estimated through
sophisticatedly designed algorithm. Moreover, we propose a supporting method
based on extended array signal estimation, which utilizes the phase changes of
different frequency subcarriers within different OFDM symbols to estimate the
distance and velocity of dynamic targets. Interestingly, the proposed sensing
scheme only needs to transmit and receive the signals once, which can be termed
as You Only Listen Once (YOLO). Compared with the traditional ISAC method that
requires time consuming beam sweeping, the proposed one greatly reduces the
sensing overhead. Simulation results are provided to demonstrate the
effectiveness of the proposed scheme.
