Synchronization of Wide Area Multilateration Systems by GNSS Common View Techniques Mauro Leonardi #1 , Luca Bellipanni #2 , Gaspare Galati #3 # Tor Vergata University Via del Politecnico 1,00131 Rome, Italy 1 leonardi@disp.uniroma2.it 2 lucab20@libero.it 3 galati@gmail.com Abstract In this work the application of the GNSS Common View (CV) synchronization techniques to a Mode S Wide Area Multilateration System is analyzed. These synchronization techniques uses the GNSS (GPS or in the future Galileo) satellites to distribute a common clock to the various stations dislocated on a given coverage area. Due to the high stable atomic clock on the satellites and to the very low cost of the GNSS receiver, this is very convenient for many (non safety critical) applications. In this paper the CV techniques is tested for WAM stations synchronization. After an introduction a real case study is reported and some trials with real data are presented. I. I NTRODUCTION Wide Area Multilateration (WAM) is a form of Cooperative Independent Surveillance based on the the principle of hyperbolic localization of mobiles that emit SSR Mode S signals [1]. A WAM system consists of a number of station receiving the signal from the target and a central processing unit calculating the target’s position from the time difference of arrival (TDOA) of the signal at the different antennas (Figure 1 [2][3]). WAM can be successfully used for en-route monitoring (up till 350 Km), terminal area monitoring (up till 100 Km) and as an integration of Automatic Dependent Surveillance-Broadcast systems (ADS-B). Fig. 1. WAM localization technique. The accuracy of WAM systems is strongly dependent on the precision of Time Stamp assigned by each station to the received signal from the target. Consequently, a fundamental requirement is the complete synchronization of the system to a sigle common reference time: the classical approach uses of a Reference Trasponder (RT). Using Reference Transponder is possible to achieve the receiver stations synchronization: the RT, in fixed and known position, emits a Mode S reply as the real target do. Knowing the reference trasponder position the central processing unit it is possible to compute the clock offset of each receiving station. Reference Transpon6der need to be in line of sight to each receiver. For a WAM system this is the mayor limitation due to the distance between the stations that could be up to 100 Km and any type of obstacle that could be in the line of sight to the reference transponder and the receiving stations. Using a time synchronization based on a satellite system this problem could be reduced. The paper is organized as follows: the first section presents the principles of GNSS synchronization and focus on the Common View method, in second section the application of Common View techniques to a typical WAM configuration is presented.