Potential Threats by a Symmetric Deployment of Replay Devices Against Synchronization via a Navigation Satellite System

Usage of a navigation satellite system is widely spread into time transfer to receivers used in infrastructure. Recently, many static receivers are used for time synchronization via a satellite navigation system and are more threatened by deliberate spoofing than dynamic receivers. In defense of social infrastructures, countermeasures based on difficulties for a spoofing signal to keep a position estimator of a target receiver close to its true position have been proposed. In the present paper a symmetric deployment against a target receiver of replay devices is analyzed. It is shown that a pair of replay devices can create the same constant delay of cross correlation peak of the receiver against L1 C/A signals emitted by GPS satellites independent of their elevation and azimuth angles. When all pseudo ranges of a receiver are uniformly shifted, the position estimator of the receiver is kept unchanged. A replay device can be realized by less cost than GPS signal generator based spoofer due to its limited functionality. Countermeasures based on signal decomposition is introduced. It can detect fraudulent signal even when a composed signal keeps position estimator of a receiver unchanged.