  Integration of radar, wireless communications, and spectrum sensing is being
investigated for 6G with an increased spectral efficiency. Microwave photonics
(MWP), a technique that combines microwave engineering and photonic technology
to take advantage of the wide bandwidth offered by photonics for microwave
signal generation and processing is considered an effective solution for the
implementation of the integration. In this paper, an MWP-assisted joint radar,
wireless communications, and spectrum sensing (JRCSS) system that enables
precise perception of the surrounding physical and electromagnetic environments
while maintaining high-speed data communication is proposed and demonstrated.
Communication signals and frequency-sweep signals are merged in the optical
domain to achieve high-speed radar ranging and imaging, high-data-rate wireless
communications, and wideband spectrum sensing. In an experimental
demonstration, a JRCSS system supporting radar ranging with a measurement error
within $\pm$ 4 cm, two-dimensional imaging with a resolution of 25 $\times$
24.7 mm, wireless communications with a data rate of 2 Gbaud, and spectrum
sensing with a frequency measurement error within $\pm$ 10 MHz in a 6-GHz
bandwidth, is demonstrated.
