GNSS Jamming Detection with Automatic Gain Control (AGC) and Carrier-to-Noise Ratio Density (CNO) Observables from a COTS receiver

As rail transport moves toward higher degrees of automation under initiatives like the R2DATO project [1], accurate and reliable train localization has become essential. Global Satellite Navigation System (GNSS) is considered as a main technology in enabling operational advancements including Automatic Train Operation (ATO), moving block signaling, and virtual coupling, which are the core components of the Horizon Europe 2024 rail digitalization agenda. However, GNSS signal integrity is increasingly threatened by intentional and unintentional radio frequency interference (RFI). This include jamming and spoofing, which are particularly concerning as the broadcasted signal can deliberately disrupt or manipulate the GNSS signal. - Jamming refers to an intentional form of interference that induces disturbances in the GNSS band, causing performance degradation or can even entirely block the receiver from acquiring the satellite signals. - Spoofing involves broadcasting counterfeit satellite signals to deceive the GNSS receiver, leading to inaccurate estimation of position, navigation and timing information. This concern about interference is not unique to rail applications. The aeronautical sector has long recognized the risks posed by GNSS interference, with extensive documentation on its impact on navigation, landing procedures, and surveillance systems. In recent years, awareness of these risks has expanded to other transport sectors. Within the automotive industry, particularly in Intelligent Transport Systems (ITS), several studies [2][3][4] have addressed the vulnerability of GNSS against interference. Similar concerns are now emerging in the rail domain [5][6][7], especially as GNSS is increasingly adopted in safety-critical applications. In literature, several levels of actions have been explored, ranging from merely the detection of a malicious signal at the initial phase to the application of advanced signal processing methods aimed at suppressing the effects of interference [8]. In alignment with the goal of the R2DATO project, we evaluated the impact of various classes of interference signals such as amplitude modulation (AM), frequency modulation (FM), pulsed, frequency hopping and chirp signals on the GNSS observables including Automatic Gain Control (AGC) and Carrier to Noise Ratio (CNO) as measured by a Commercial Off-The-Shelf (COTS). However, in this work, the analysis is only limited to impact of chirp interference on GPS L1 receiver observables and detection performance.

A framework for GNSS-based solutions performance analysis in an ERTMS context

Context Progresses in GNSS-based solution introduction in rail applications GNSS (Global Navigation Satellite System) is now used in most of our travels and each of our smartphone apps. Most of the usages are not safety-critical. But Europe identified GNSS for more applications and to be integrated in rail in general as part of the toolset to help railway to contribute to reduce transport carbon footprint. To increase the use of trains in European transports, railways must improve their attractiveness for passengers and freight, but also increase reliability, availability and efficiency by reducing capital expenditure and operational costs. GNSS is part of the global digitalization scheme of freight that aims to offer added value to the clients knowledge of accurate time of arrival, continuous monitoring of transport conditions (temperature, humidity...). But a major challenge will be to reach stringent applications and in particular, GNSS is today seen as a realistic and serious game changer for the future of the ERTMS (European Rail Traffic Management System). The localisation function is today performed with both odometry and balises. Odometer provides a continuous train position in time from a reference point. But as the distance delivered by the odometer shows a growing bias with distance, due to wear and wheel sliding, the use of on-track balises allows to reduce this error. Future systems will be based on on-board localisation solutions with GNSS receivers. It will allow the development of new concepts for moving blocks, virtual coupling and automation. Its use for train integrity is also investigated. But the environmental conditions of track and surroundings configuration, i.e, tunnels, dense urban areas or vegetation often degrade positioning performance and thus its efficiency and safety. Indeed, GNSS satellites are moving and their visibility (availability and relative position from the receiver) vary with time. Moreover, for optimal performance, the system requires open sky environments, which are the cases of most of the aeronautical uses but not of train uses. Trains often circulate in areas where signal reception can be disturbed (multipath, intentional or unintentional interferences) and thus, performances degraded. If many progresses have been made in the past years to develop more robust receivers [Puccitelli, 2022], multi-sensor solutions [CLUG website] or missing tools such as Digital Maps [Crespillo, 2023], in projects such as the Shift2Rail Project X2Rail-5 or CLUG, some questions remain and in particular related to performance evaluation. How can we evaluate performances in a dynamic environment (train, satellite, obstacles)? How can we be sure that every configuration has been tested? What is the impact of a failure (inaccuracy, missed detection) on operation? Some of these issues are addressed in the on-going R2DATO project funded by Europe's rail.