Since the end of the 80’s, Global Navigation Satellite Systems (GNSS) are available for remote atomic clock comparisons, especially the Global Positioning System (GPS). Continuously transmitted signals are used to measure the offset between one ground clock and one atomic clock on-board, which allows to relate the ground clock to the common system time scale under given conditions. When another station carries out similar measurements simultaneously, the offset between both ground clocks can be computed according to the Common-View technique. Most recent comparison techniques are based either on code signals, or on carrier frequencies, or on a combination of both signal types. Additional products generated by the International GNSS Service (IGS), a worldwide network of observation and computation stations, are allowing for an improvement of time transfer uncertainties. The IGS station OPMT is located in Observatoire de Paris (OP) and managed by SYRTE as a contribution to IGS. Comparisons of remote atomic standards are however limited today by the determination of the hardware propagation delays, which state of the art expanded uncertainties are about 1.5 ns to 3.0 ns (k = 2). During the recent years, SYRTE has become a reference laboratory for the relative calibration of receiver hardware delays. In particular, a direct comparison between GPS time transfer and Time Transfer by Laser Link (T2L2), which was developed by Observatoire de la Côte d’Azur (OCA) and by the French Space Agency (CNES), lead to a maximum deviation of 240 ps, the two techniques having been calibrated independently. As a European Metrology laboratory, LNE-SYRTE is also involved in internal developments of European navigation systems EGNOS and Galileo, by providing the connections to the local prediction of UTC called UTC(OP), and by achieving relative calibration of the links between the atomic clocks located either in other European laboratories or in the Galileo Earth stations.