## 1 Introduction  
Civilian geopositioning systems are experiencing explosive growth. A recent analysis of the Global Navigation Satellite System (GNSS) market shows two main application areas accounting for the majority of the market, which are intelligent transportation systems (ITSs) and location-based services. The modernization of U.S. Global Positioning Systems (GPSs) [1, 2], Russia's GLONASS (Globalnaya Navigatsionnaya Sputnikovaya Sistiena) [3] and the development of Europe's Galileo [4, 5], China's BeiDou [6, 7], as well as Japan's QZSS (Quasi-Zenith Satellite System) [8, 9] are progressing at a rapid pace, introducing expanded capability potential and higher performance levels for satellite positioning. The above is leading to new developments in system architecture, providing an opportunity for the development of new positioning strategies. Currently, GNSS is considered the best system for providing the ability to determine precise position globally, along with the ability to determine the speed and time of a localized object [10].  
Detecting the current location of rail vehicles on the rail infrastructure network determines the safety, efficiency, and reliability of rail transportation. In addition, it indirectly affects safety at rail-road crossings, i.e., road safety, as well. In terms of the efficiency and reliability of transportation systems, the ability to detect a moving vehicle can improve the effective capacity of railway lines. As with technical diagnostics, effective identification of the current state of the transportation network determines the efficiency of the transportation system. The development of railways, with particular emphasis on high-speed railways, necessitates the modernization and improvement of traffic control equipment and systems. A special area of development, ensuring the safe and efficient use of rail transport, is the detection and localization of rail vehicles moving on the rail infrastructure [11; 12]. The ability to accurately determine the position of a rail vehicle with a high degree of accuracy is a key element in the reliable operation of rail transportation. Therefore, in the field of rail vehicle detection and localization equipment and systems, there is a lot of research and analysis aimed at developing existing or creating new solutions dedicated to rail vehicle positioning [13].  
Mobility data based on GNSS tracking is widely used in many areas, such as travel pattern analysis [14], security research [15; 16], transportation efficiency [1; 17], and travel impact assessment. Within the transportation system, modes of transport are important mobility tools whose level of reliability is critical to the functioning of the flow of goods and movement of people [18]. This article aims to synthesize a review of the current state of the literature and practical solutions for identifying potential areas of application of GNSS in positioning, along with characterizing the available GNSSs, without making explicit recommendations on which system to use. In addition, this article focuses on identifying the basic characteristics and parameters that define functionality in the potential use of GNSS as part of a system responsible for positioning rail vehicles in railway infrastructure. In order to be able to implement satellite positioning systems for railway applications, knowledge of GNSS architecture is essential. Based on the available literature and applied technical and application solutions, it is necessary to define the general architecture of positioning systems, together with the definition of the relationship between satellite positioning and the logic of operation of the available railway guidance and control systems.