## 1 Introduction  
The global positioning system (GPS) technology exhibits several advantages, such as easy to obtain absolute position solution, weather independence, autonomous operation, and not requiring a line-of-sight between target points [1]. This provides a great opportunity for the monitoring of displacement or deflection of bridges under different loading conditions in real time. Recent studies have demonstrated the feasibility of deploying GPS receivers as'smart sensors' for the dynamic monitoring of bridges [2]. [PERSON] and [PERSON] et al. are the early researchers that used integrated GPS and accelerometers to monitor the deflection of bridges [3,4]. [PERSON] et al. found that GPS is suitable in the identification of dynamic characteristics of even relatively rigid (modal frequencies up to 4 Hz) civil engineering structures that are excited by various loads (wind, traffic, earthquakes, etc.) if the displacements are less than the uncertainty level of the method (such as 5 mm) [5]. Efforts have been made in recent years in the use of an integrated monitoring system that consists of dual frequency GPS or Global Navigation Satellite System (GNSS) receivers and triaxial accelerometers for the detection of the dynamics of long span road bridges [6,7]. Recently, bridge monitoring was implemented using the BeiDou Satellite Navigation System (BDS)-Real-Time Kinematic (RTK) and GPS-RTK techniques [8]. Although high accuracy demanding users can typically observe an average number of 8-10 GPS satellites, actually, in several moments of one day, the number of available satellites may decrease to 4-6 or many such satellites are low-elevation ones. In these cases, GPS constellation cannot maintain high-accuracy in a single-frequency single-epoch (SFSE) positioning model [9]. Accordingly, the application of a multi-GNSS system can significantly improve the positioning performance. [PERSON] et al. demonstrated that the positioning performance of BDS in the Asia-Pacific region is comparable to that of GPS [10]. The Quasi-Zenith Satellite System (QZSS) has been operated as a four-satellite constellation since November 2018, and three satellites can be available at all times to users in the Asia-Oceania region. Hence, both the QZSS and BDS systems can be used to improve the performance of GPS positioning in the above regions [11]. However, for European users, the Galileo Satellite Navigation System (Galileo) can only be used to improve the robustness and accuracy of GPS precise positioning. By launching the first four Galileo satellites in pairs, on 21 October 2011 and 12 October 2012, the Galileo system successfully concluded the In-Orbit Validation (IOV) phase at the end of 2013. Currently, Galileo has 23 satellites in the operational orbits and all transmit data on three carrier frequencies ([[http://esamultimedia.esa.int/docs/Galileo](http://esamultimedia.esa.int/docs/Galileo)]([http://esamultimedia.esa.int/docs/Galileo](http://esamultimedia.esa.int/docs/Galileo))). In addition, it is stated on the Galileo website that initial services were made available by the end of 2016 and system completion is scheduled for 2020 [12]. A project, named GEO6, was oriented to define and implement new applications of Galileo. As such an example, the GNSS and Earth Observation for Structural Health Monitoring (GeoSHM) system, which is funded by the European Space Agency, is a project that applies GNSS (including Galileo) and Earth Observation techniques to monitoring bridge deformation [7]. Since the plan for the Galileo satellites was proposed, the potential benefits of the single Galileo or integrated Galileo/GPS navigation system have been explored. The two key required navigation performance (RNP) parameters, i.e., accuracy and integrity, were addressed in detail. The results showed significant improvements in accuracy and integrity when a integrated constellation is used rather than Galileo alone [13].