Low-Cost Pseudolites: A Loop-Back Time Synchronization Scheme for Pseudolites Using Real-Time Clock Offset Calibration for Reliable PNT

This paper presents the development of a cost-effective pseudolite (PL) transmitter assembly capable of transmitting a GNSS-like signal for navigation. A novel loop-back time synchronization scheme is introduced, which utilizes PL pseudorange observations over a predefined cable length to achieve real-time clock offset calibration, ensuring reliable position, velocity and time (PVT) solutions. The paper details the PL signal design, transmitter hardware implementation and the loop-back time synchronization framework providing validation results using a GNSS signal simulator over pre-defined cable lengths with a RMSE within 1 m. Moreover, single point positioning (SPP) results are presented for measurement scenarios using both GNSS-only and GNSS combined with the PL signal in terms of positioning accuracy and dilution-of-precision (DOP) metrics. The combined use of the PL signal with GPS shows an overall improvement in DOP metrics and a reduction in vertical position error by approximately 3 meters. Overall, the presented transmitter architecture eliminates the need for expensive synchronization hardware and complex timing protocols and lays foundation for easily deployable ground-based PL transmitters.