  In this paper, we propose a novel scheme for sixdimensional (6D) radar
sensing and tracking of dynamic target based on multiple input and multiple
output (MIMO) array for monostatic integrated sensing and communications (ISAC)
system. Unlike most existing ISAC studies believing that only the radial
velocity of far-field dynamic target can be measured based on one single base
station (BS), we find that the sensing echo channel of MIMO-ISAC system
actually includes the distance, horizontal angle, pitch angle, radial velocity,
horizontal angular velocity, and pitch angular velocity of the dynamic target.
Thus we may fully rely on one single BS to estimate the dynamic target's 6D
motion parameters from the sensing echo signals. Specifically, we first propose
the long-term motion and short-term motion model of dynamic target, in which
the short-term motion model serves the single-shot sensing of dynamic target,
while the long-term motion model serves multiple-shots tracking of dynamic
target. As a step further, we derive the sensing channel model corresponding to
the short-term motion. Next, for singleshot sensing, we employ the array signal
processing methods to estimate the dynamic target's horizontal angle, pitch
angle, distance, and virtual velocity. By realizing that the virtual velocities
observed by different antennas are different, we adopt plane fitting to
estimate the radial velocity, horizontal angular velocity, and pitch angular
velocity of dynamic target. Furthermore, we implement the multiple-shots
tracking of dynamic target based on each single-shot sensing results and Kalman
filtering. Simulation results demonstrate the effectiveness of the proposed 6D
radar sensing and tracking scheme.
