Optimizing Spectrum Sensing in Cognitive Geo- Leo Satellite Networks: Overcoming Challenges for Effective Spectrum Utilization

The rapid growth of wireless and satellite technologies has increased the demand for efficient use of the electromagnetic spectrum. Cognitive satellite networks offer a promising solution, with spectrum sensing being crucial for the optimal utilization of radio-frequency (RF) resources. However, in cognitive satellite networks, characterized by excessive propagation delays, the effectiveness of spectrum sensing depends on the strategic placement of sensing nodes. This article represents the first endeavor in the literature to investigate optimal spectrum-sensing locations considering propagation delay for effective spectrum utilization in cognitive satellite networks. We begin by examining the geostationary (GEO) satellite downlink spectrum availability for cognitive technology through observations of the Inmarsat-4 F1 satellite downlink activities. We then analyze the impact of propagation delays on spectrum sensing in cognitive dual-satellite networks (CDSNs), where low-Earth orbit (LEO) satellites share the spectrum allocated to GEO satellites. Additionally, we address a critical design consideration: tracking GEO frequencies against Doppler shifts at LEO satellites, which significantly affects the effectiveness of spectrum sensing by LEO satellites. Finally, we explore future research directions in spectrum sensing within cognitive GEO-LEO satellite networks.