Photonic-Assisted Joint Radar and Communication System Using Overlapped Spectrum for High-Resolution Ranging and High-Speed Data Transmission

We propose and demonstrate a photonic-assisted joint radar and communication (JRC) system using a JRC signal with overlapped spectrum to support simultaneous wideband ranging and high-speed communications. For radar ranging, an electrical linearly-frequency-modulated (LFM) waveform is modulated on an optical carrier at a Mach-Zehnder modulator (MZM) biased at the null point to generate odd-order sidebands. By filtering out the first-order sidebands, two third-order sidebands are obtained. By beating the two sidebands at a photodetector (PD), a frequency-sextupled electrical LFM with sextupled bandwidth is generated. For wireless communications, a binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK) signal is modulated on one of the third-order sidebands. By beating the modulated sideband with the other unmodulated sideband, a frequency upconverted wireless signal is generated. The JRC signals are radiated to free space. At the radar receiver, the echo signal is applied to another MZM where the signal is optically dechirped to extract the target information. At the communication receiver, the JRC signal is received and applied to an MZM, where the radar and the communication signals beat to generate the original communication signal. Since no local oscillator (LO) signal is employed, the system is greatly simplified. The dual functions of the system are evaluated by an experiment. For radar ranging, a wideband LFM radar signal with a 9.6-GHz bandwidth is generated, and radar ranging with a high range resolution of 2.5 cm is obtained. For wireless communication, a 4-GBaud/s BPSK and a 2-GBaud/s QPSK signal are transmitted over 20 m, with the bit error rates (BERs) of $1.82\times 10^{-5}$ and $1.96\times 10^{-5}$ , respectively, which are below the forward error correction (FEC) limit for error free communications.