###### Abstract  
Today, a substantial portion of global trade is carried by sea. Consequently, the reliance on Global Navigation Satellite System (GNSS)-based navigation in the oceans and inland waterways has been rapidly growing. GNSS is vulnerable to various radio frequency interference. The objective of this research is to propose a resilient Multi-Frequency, Multi-Constellation (MFMC) receiver in the context of maritime navigation to identify any GNSS signal jamming incident and switch to a jamming-free signal immediately. With that goal in mind, the authors implemented a jamming event detector that can identify the start, end, and total duration of the detected jamming event on any of the impacted GNSS signal(s). By utilizing a jamming event detector, the proposed resilient MFMC receiver indeed provides a seamless positioning solution in the event of single-frequency jamming on either the lower or upper L-band. In addition, this manuscript also contains positioning performance analysis of GPS-L5-only, Galileo-E5a-only, and Galileo-E5b-only signals and their multi-GNSS combinations in a maritime operational environment in the Gulf of Finland. The positioning performance of lower L-band GNSS signals in a maritime environment has not been thoroughly investigated as per the authors' knowledge. GNSS vulnerability; jamming; satellite navigation 2022222294  
minder that availability, reliability, and continuity are critical, and even a slight degradation in signal quality may result in safety hazards and outages that can cost invaluably. Currently, there are four global GNSS systems that transmit PNT signals in multiple-frequency bands. Therefore, modern GNSS receivers could take advantage of Multi-Frequency, Multi-Constellation (MFMC) diversity to offer a reliable PNT solution in the event of signal disruption in one of the frequency bands. The MFMC diversity will increase the availability, reliability, and continuity of PNT solution if utilized intelligently. In [7], author presented an analysis of multi-GNSS Precise Point Positioning (PPP) performance in the maritime environment. The number of satellites per constellation, Dilution of Precision (DOP), and 2-Dimentional positioning accuracy were analyzed using a professional-grade maritime receiver. The article did not assess the impact of jamming on positioning accuracy. In [8], researchers demonstrated single- and multi-GNSS performance in terms of satellite coverage and availability using GNSS data from International GNSS Service (IGS) stations in coastal areas. Articles [9; 10; 11] investigated the detection of radio frequency interference and related threats in the maritime environment. The studies were mostly focused on the detection and mitigation of intentional and unintentional interference. The impact and consequence of real-life jamming on GPS signals in the maritime environment were discussed in [12]. The authors proposed an Enhanced Loran (eLoran)-based system diversification to reduce GNSS vulnerability in case of signal disruption. The impact of jamming on maritime GNSS receivers in Norwegian shore was addressed in [13]. The study also presented partial positioning performance assessments of different GNSS signals, particularly GPS L1 and GLONASS G1. So far, there have been limited results presented in the literature about the impact of jamming on the positioning accuracy of a marine vessel in a real-life operational environment. The objective of this research is to immediately identify any jamming incident on any of the GNSS signals and to propose a resilient MFMC receiver to offer an uninterrupted positioning solution in the event of single-frequency or single-constellation jamming. The authors first implement a jamming event detector based on received signal strength along with other modifications of a GNSS software receiver. Furthermore, the influence of jamming on legacy GNSS signals received on the L1/E1/B1 frequency bands is presented. The impact of jamming on positioning accuracy is also analyzed separately on L5/E5 frequency band.