The GNSS-Transceiver: Using vector-tracking approach to convert a GNSS receiver to a simulator; implementation and verification for signal authentication

Studying and testing new and possible future GNSS signals and navigation messages require a signal generator which is flexible and fully modifiable. To overcome the need of implementing a signal generator from scratch, we present a way to modify an excising GNSS software receiver (SR) into a software transceiver (ST). The ST reuses the SR modules and the infrastructure for the signal generation. The modification approach is based on exploiting the vector tracking feature of the software receiver. Due to the replacement of the position in the vector tracking loop, it is possible to manipulate the numerical controlled oscillator (NCO) and thereby force the code and carrier generator to generate a signal replica which fits to the induced position. Multiplying the replica with the desired symbol value and the desired amplitude yields an entire line of sight signal. The replica signals of all satellites in tracking match the predefined user trajectory. Saving the added replica signals results in a signal stream of intermediate frequency (IF). The ST is able to track, generate or re-generate tracked signals. The concept and an implementation approach is presented. The signal quality is compared to real signals. The possibilities of the ST are shown by generating Galileo OS signals with navigation message authentication (NMA) and generating a secure code estimation (SCE) attack signal.