  Integrated Sensing and Communication(ISAC) has become a key technology for
the 5th generation (5G) and 6th generation (6G) wireless communications due to
its high spectrum utilization efficiency. Utilizing infrastructure such as 5G
Base Stations (BS) to realize environmental imaging and reconstruction is
important for promoting the construction of smart cities. Current 4D imaging
methods utilizing Frequency Modulated Continuous Wave (FMCW) based Fast Fourier
Transform (FFT) are not suitable for ISAC scenarios due to the higher bandwidth
occupation and lower resolution. We propose a 4D (3D-Coordinates, Velocity)
imaging method with higher sensing accuracy based on 2D-FFT with 2D-MUSIC
utilizing standard 5G Downlink (DL) millimeter wave (mmWave) signals. To
improve the sensing precision we also design a transceiver antenna array
element arrangement scheme based on MIMO virtual aperture technique. We further
propose a target detection algorithm based on multi-dimensional Constant False
Alarm (CFAR) detection, which optimizes the ISAC imaging signal processing flow
and reduces the computational pressure of signal processing. Simulation results
show that our proposed method has better imaging results. The code is publicly
available at https://github.com/MrHaobolu/ISAC\_4D\_IMaging.git.
