## 2 Methodology for Reviewing the Current State of Knowledge
In accordance with the above, it was identified that the topics of the publication primarily focus on issues related to the definition of the architecture of the system based on localization of rail vehicles using GNSS. In this context, issues related to the architecture of multi-sensor systems, the use of digital maps in the implementation process of satellite systems, and the functioning and dependencies of GNSS segments were addressed. The above will clarify areas where the analysis of the feasibility of using satellite systems in rail transportation has some shortcomings for the implementation process. The GNSS implementation process itself in the literature review methodology will make it possible to identify a potential area for development and modification, adjusting technical and formal requirements. In addition, the literature review methodology takes into account the characteristics of individual satellite positioning systems due to the potential impact on rail traffic safety resulting from the use of specific systems or all systems available for positioning rail vehicles. At the stage of initial selection of the state-of-the-art review, the number of citations of a given article and the IF (impact factor) index were used as one of the bibliometric indicators in determining the suitability of articles for this review. This review takes  
According to the trend presented in Table 1, it can be observed that in the interval of the last two decades, the interest in the scientific community in the topic of GNSS implementation in railway infrastructure is gradually increasing. A significant increase is observed since 2015. The growth slows down in 2021-2023, which can be attributed to the constraints of the COVID-19 pandemic. By the publication deadline of 2024, the number of literature items shows a potency for an upward trend in terms of a three-year perspective. Given the application of the PRISMA standard, the following steps in the literature review process were defined:  
* Research question--\"In what areas is it possible to apply Global Navigation Satellite Systems for rail vehicle positioning? How should the dependencies of satellite positioning systems be linked to rail traffic control systems?\"
* Literature search--A systematic literature search was conducted using various online databases. The following terms were used in the above databases: \"development of positioning systems\", \"GNSS\", \"satellite navigation\", \"rail vehicle positioning\", \"rail vehicle positioning systems\", \"railway safety criteria\", and \"implementation of satellite positioning systems\". The choice of key words was based on the need to include separate issues for conventional approaches to rail vehicle detection and positioning, as well as future positioning solutions in the form of the use of satellite systems. * Selection of articles--Articles were pre-screened based on their titles and abstracts, and then full-text analysis was carried out after selecting appropriate articles. The criteria for deciding whether to include an article in the reference list were whether the articles focus on GNSS issues in the area of railway applications with consideration of articles discussing case studies or practical applications and articles published in English. The following were used as exclusion criteria: articles unrelated to the research question. Data were then extracted and synthesized from selected articles, including information on satellite positioning system implementations, case studies, challenges, and future directions. * Analysis and Interpretation--Data were analyzed and interpreted to identify common themes and patterns, as well as challenges and limitations of current projects and research. * Writing and dissemination--The result of the conducted literature review was synthesized into a review article. This article was subject to review by competent reviewers to confirm its accuracy and complementarity, and then published. * Registration--This systematic review was not registered in a publicly accessible database.