# A Proposal of a Troposphere Model in a GNSS Simulator for VANET Applications
###### Abstract  
Vehicle positioning is becoming an important issue related to Intelligent Transportation Systems (ITSs). Novel vehicles and autonomous vehicles need to be localized under different weather conditions and it is important to have a reliable positioning system to track vehicles. Satellite navigation systems can be a key technology in providing global coverage and providing localization services through many satellite constellations such as GPS, GLONASS, Galileo and so forth. However, the modeling of positioning and localization systems under different weather conditions is not a trivial objective especially considering different factors such as receiver sensitivity, dynamic weather conditions, propagation delay and so forth. This paper focuses on the use of simulators for performing different kinds of tests on Global Navigation Satellite System (GNSS) systems in order to reduce the cost of the positioning testing under different techniques or models. Simulation driven approach, combined with some specific hardware equipment such as receivers and transmitters can characterize a more realistic scenario and the simulation can consider other aspects that could be complex to really test. In this work, the main contribution is the introduction of the Troposphere Collins model in a GNSS simulator for VANET applications, the GPS-SDR-SIM software. The use of the Collins model in the simulator allows to improve the accuracy of the simulation experiments throughout the reduction of the receiver errors.  
positioning system; VANET; troposphere model; GNSS simulator; GPS receiver 2021  
30 March 20213 April 20213  
racy and reliability correcting measurement errors and providing information integrity on signals.  
Today the navigation systems are considered an integrated part of the Intelligent Transportation System (ITS) and Vehicular Ad-Hoc Network (VANET) system [5]. The vehicles are equipped with GPS receivers and, in the next future, all vehicles will have a GNSS receiver on board [6; 7]. In Figure 1 a typical scenario of global position system in a VANET environment is shown.  
The vehicles network aims to improve road safety, increase traffic efficiency and save energy giving also attention to the emission issues [8; 9], and also different works focus their attention on mechanisms to warn dangerous or emergency situations by exploiting on-board sensors [10], for routing purposes [11] and also using predictive mechanism as in [12; 13]. Incoming automatic driving applications are going to require even tighter level of precision and security in order to guarantee the high required standard. The first sector using detailed GNSS integrity solutions is that of aviation.  
In this paper, taking as reference scenario the field of vehicles' applications, we propose the integration on the Troposphere Collins model [14] inside a well known GNSS simulator called GPS-SDR-SIM written in \(C\) language and able to generates GPS baseband signal data streams, which can be converted to RF using software-defined radio (SDR) platforms. So, the simulation modeling is integrated with real equipment and real data elaborated by GPS receivers. In particular, the proposed module, implementing the Troposphere Collins model, is able to improve the accuracy of the simulation experiments.  
The rest of this paper is organized as follows: Section 2 provides some related works about considered topic. In Section 4, a description of the GNSS applications in VANET scenario is given. In Section 5, we describe the used simulator considered for developing additional software module. The numerical results are presented in Section 6. Finally, Section 7 concludes the paper.