State of the art on global navigation satellite systems: a comparative study of GPS, GLONASS, and Galileo

Global Navigation Satellite Systems (GNSS) are essential for providing positioning, navigation, and timing (PNT) services in various fields such as aerospace, defense, transportation, and scientific research. The three primary GNSS: Global Positioning System (GPS, USA), Global Navigation Satellite System (GLONASS, Russia), and Galileo (European Union), vary in their architecture, frequency bands, signal structures, and levels of accuracy. This paper offers a comprehensive comparison, examining their technological advancements, performance, modernization initiatives, and future outlook. Furthermore, we assess the integration of multiple GNSS, emphasizing how hybrid receivers that utilize various constellations can achieve enhanced accuracy, resilience, and redundancy. Our analysis is based on a thorough literature review, which includes research studies, official technical documents, and performance reports, providing a detailed examination of each system's strengths, challenges, and practical applications.