With the continuous advancement of wireless communication and information technology, mobile data transmission volume has nearly doubled each year. Simultaneously, the proliferation of access devices and the widespread adoption of emerging technologies such as the Internet of Things (IoT), high-definition live streaming, virtual reality (VR), and augmented reality (AR) have intensified the pressing demand for high-speed communication. Nevertheless, meeting the substantial data transmission requirements remains a formidable challenge given the current communication frequencies and bandwidth limitations. The currently utilized sub-6 GHz frequency band has become relatively congested, while the frequency range spanning from 6 GHz to 300 GHz in the millimeter wave spectrum remains largely untapped, offering an exceptionally abundant spectrum resource. Furthermore, in comparison to the lower microwave frequency bands currently in commercial use, the absolute bandwidth available in the millimeter wave frequencies significantly surpasses that of the lower microwave bands. In recent years, transmission systems combining radar sensing with communication have garnered increasing attention. To mitigate the strain on the limited spectrum resources and reduce power consumption, radar and wireless communication emerge as paramount and pivotal applications within the domain of radio frequency (RF) technology. However, as technology continues to evolve, radar and communication are converging towards integrated design, whereas they are initially developed and designed independently, each catering to their distinct functions and frequency bands.
In this study, we presented an experimentally photonics-aided integrated radar and communication system. On the transmission side, the integrated signal was generated by encoding a quadrature phase shift keying (QPSK) signal onto a linear frequency-modulated (LFM) signal in the baseband, with the primary objective of eliminating the need for digital-to-analog conversion (DAC) in the intermediate frequency (IF) band. Subsequently, the joint radar communication (JRC) signal was modulated onto an optical carrier and mixed with another external cavity laser (ECL) to generate the millimeter wave LFM-QPSK signal. The adoption of QPSK encoding ensured a constant envelope for the JRC signal, a crucial aspect of long-distance radar sensing. On the receiving side, a W-band horn antenna (HA) captured a portion of the JRC signal for transmission purposes. This signal was then down-converted to an IF band by using a W-band mixer. Following de-chirping and a series of digital signal processing (DSP) steps, the QPSK signal was recovered. For radar sensing purposes, the echo signal was initially down-converted to the baseband and subsequently processed through a matched filter. Due to the well-preserved cross-correlation characteristics of the original LFM signal in the resulting millimeter wave JRC signal, precise radar synchronization was obtained through pulse compression. Consequently, this system could achieve both high-resolution radar sensing and high-speed communication functions.
We introduce a W-band communication-aware integrated system, and its schematic diagram and algorithmic process are depicted in Fig. 2. This system successfully achieves robust communication and sensing capabilities through offline processing at the radar and communication receiver. As shown in Fig. 4, employing the de-chirping operation at the communication receiver allows us to successfully extract high-quality communication sequence signals from the integrated waveform. Subsequent offline DSP algorithms enable us to achieve communication with a significantly lower error rate than that of the hard decision threshold. As shown in Fig. 5(a), (b), and (c), we conduct experiments in different scenarios at distances of 2, 10, and 50 m, respectively. When the input power into the PD exceeds -1 dBm, each component of the integrated signal achieves high-quality communication below the hard decision threshold. Additionally, by introducing an extra frequency offset error component, the integrated signal maintains high communication quality, as demonstrated in Fig. 5(d), proving the system's robustness. On the radar sensing side, we employ pulse compression techniques to detect single and dual targets with a radar accuracy of approximately 2.0 cm. Figure 7 displays the pulse compression output results for a single target at different distances, while Fig. 8 shows the results for dual targets at varying distances. In a word, clear target detection is achieved at the radar end. These experimental results underscore the effectiveness of the proposed W-band communication-aware integrated system.
In this study, we have proposed and demonstrated a photonics-aided system for joint communication and radar sensing. The baseband signal is achieved by encoding an LFM with a QPSK signal. The orthogonal properties of the LFM signal enable signal demodulation, while pulse compression is utilized for radar detection. Experimental results indicate that, through signal-sharing techniques, we can achieve a distance resolution of 2.0 cm and high-quality transmission at speeds of up to 20 Gbit/s within the 91 GHz frequency band, with transmission distances of up to 50 m. Furthermore, this system allows for flexible signal type adjustments as needed, making it a promising candidate for future millimeter-wave communication applications.
