  Orthogonal frequency division multiplexing (OFDM)-based integrated sensing
and communication (ISAC) is promising for future sixth-generation mobile
communication systems. Existing works focus on the joint estimation of the
targets' range and velocity for OFDM-based ISAC systems. In contrast, this
paper studies the three-dimensional joint estimation (3DJE) of range, velocity,
and azimuth for OFDM-based ISAC systems with multiple receive antennas. First,
we establish the signal model and derive the Cramer-Rao bounds (CRBs) on the
3DJE. Furthermore, an auto-paired super-resolution 3DJE algorithm is proposed
by exploiting the reconstructed observation sub-signal's translational
invariance property in the time, frequency, and space domains. Finally, with
the 5G New Radio parameter setup, simulation results show that the proposed
algorithm achieves better estimation performance and its root mean square error
is closer to the root of CRBs than existing methods.
