Sub-6$\,\text{GHz}$ SAR Imaging With Frequency Hopping Toward JCAS Applications in Automotive Scenarios

As highly assisted and autonomous driving systems evolve, the need for detailed environmental information becomes crucial for accurate trajectory planning and safety assurance. To achieve this, sub-6$\,\text{GHz}$vehicle-to-everything (V2X) communication signals could be leveraged for imaging purposes, merging communication and environmental sensing. However, the low center frequencies and limited bandwidths in this joint communication and sensing (JCAS) approach pose challenges for imaging performance. This article presents a method for using bandwidths across multiple communication bands, leveraging the synthetic aperture radar (SAR) principle to combine data of various measurement points and achieve high-resolution environmental images. To accomplish this, a channel sounding measurement is performed using a 1$\,\text{GHz}$to 4$\,\text{GHz}$linear frequency modulated (LFM) sensor system. The frequency ramp is then restricted to various subband constellations for each measurement point in the SAR processing. By randomly selecting subbands within the full ramp, the performance of random frequency hopping between measurement points is quantitatively assessed. The experimental SAR results validate the theoretical predictions and anticipated imaging characteristics. Images obtained with an effective bandwidth of 100$\,\text{MHz}$remain comparable to those acquired using the full bandwidth. To assess its real-world applicability in an automotive scenario, the evaluations are applied to various environments, with a particular focus on a parking lot. Despite frequency hopping being restricted to defined communication bands and an effective bandwidth of approximately 100$\,\text{MHz}$, the resulting SAR image clearly shows targets such as cars, a bicycle, a wooden fence, bushes, and a person. This demonstrates the feasibility of sub-6$\,\text{GHz}$SAR imaging under communication constraints within a JCAS context.