A New Integrated Sensing and Backscatter Communication System Based on Phaseless Extended Rytov Approximation

This paper proposes a novel integrated sensing and backscatter communication framework based on inverse scattering methodology utilizing the extended Rytov approximation (xRA), which can operate without the need for explicit phase information. The proposed system uniquely employs phaseless received signal strength indicator (RSSI) measurements combined with dynamic tag impedance modulation to decompose RSSI data into structural and antenna mode components. This decomposition not only facilitates tag identification but also enables robust differentiation between metallic and dielectric objects with varying permittivities through xRA integration. Furthermore, the extracted antenna mode RSSI component provides essential channel state information (CSI) for backscatter communication, significantly mitigating interference from environmental objects and enhancing backscatter communication reliability. To further improve spectral efficiency and bit error rate (BER) performance, we introduce and adapt the joint permutation, group, and antenna index spatial modulation (JPGA-ISM) scheme, which transmits additional information through multi-dimensional indexing while employing low-order pulse amplitude modulation (PAM) and secondary pulse amplitude modulation (SPAM) constellations to maximize minimum Euclidean distance (MED). Comprehensive three-dimensional electromagnetic simulations validate the effectiveness of the proposed system across diverse scenarios, including single and multiple tags in the presence of various metallic and dielectric objects. It is demonstrated that the proposed system successfully detects all tags, reliably distinguishes between metallic and dielectric materials with varying permittivities, and effectively identifies individual tags even in complex environments. In addition, performance analysis of the JPGA-ISM scheme demonstrates close agreement between simulated BER and theoretical upper bounds in high signal-to-noise ratio (SNR) regions, and confirms its superior performance compared to alternative spatial modulation techniques under equivalent spectral efficiency. Unlike phase-coherent backscatter systems, the proposed phaseless approach eliminates the need for phase synchronization across receivers, significantly simplifying hardware requirements. These findings underscore the significant potential of combining advanced inverse scattering and phaseless techniques with efficient spatial modulation schemes, revealing a promising direction for the development of integrated sensing and communication (ISAC) systems in next-generation wireless applications.