Software-Defined Radio for Spectral Analysis and Integrated Sensing and Communications

Nowadays, in the actual context where wireless communications systems are becoming always more crucial, enabling heterogeneous services and massive device connections, different criticalities must be taken into consideration. In particular, spectrum congestion has become a critical issue that must be challenged; for this reason, spectrum analysis and Integrated Sensing and Communication (ISAC) can be optimal solutions to sense the radio spectrum and monitor its status or to save resources by integrating two different technology without any interference. In this background, the use of reconfigurable and software-based RF technology like Software-Defined Radio (SDR) can be an interesting proposal to overcome these well-known issues and support the solutions under investigation. This thesis is divided into three parts: in the first part, the theoretical background is presented along with a general overview of the technological aspects and the critical issues involved. In the second part of the thesis, the most relevant publications produced or submitted within this Ph.D. program are appended. Finally, in the third part conclusions and future directions are drawn. Firstly, the spectral analysis is presented with a description of the possibilities enabled by SDR technology and the different heterogeneous services that can be executed to support modern mobile communication technologies. Two SDR systems are described, the first one is capable of acquiring a certain frequency band to successively post-process it for unknown signals detection and recognition, while the second is able to actively support modern communication systems through different services, in particular, monitoring in real time the frequency band of interest, executing signal detection and localization algorithms by means of distributed SDR system. Subsequently, the advantages of ISAC approach are presented, with a particular interest in radar and communication integration. The attention will be on Synthetic Aperture Radar (SAR) systems and the possibility to integrate different functionalities thanks to SDR paradigm. In particular, two main functions will be presented; the integration of a transparent communication link, able to combine identification and localization processes in classic SAR systems without any interference in the normal imaging process. The second one will regard the capacity to reflect the SAR signal similarly to a classic Corner Reflector (CR), using all the advantages and flexibility of SDR technology.