# Characterization of a Time Transfer Channel Between a Narrow-Band Transponder on a GEO Satellite and a Ground-Based Station

## TL;DR

The paper explores using a GEO satellite transponder for time synchronization and positioning as an alternative to GNSS systems.

## Contribution

A narrow-band transponder on a GEO satellite is proposed and tested as an anchor for time transfer and positioning.

## Key findings

- A time accuracy of approximately 1 μs is achieved after integrating multiple pulses.
- The QO-100 satellite is shown to be a suitable anchor for the proposed time transfer technique.
- Channel effects are estimated and corrected using diverse signal propagation models.

## Abstract

Time synchronization and positioning of bistatic radar transceivers is required to coordinate and meaningfully merge the measurements made between them. It simultaneously allows the radar transceivers to change their position throughout time. Despite their acknowledged vulnerabilities, Global Navigation Satellite Systems (GNSSs) are the preferred source for Positioning, Navigation and Timing (PNT) services. Because of these vulnerabilities however, research on possible signal sources to obtain alternative positioning, navigation and timing (A-PNT) is of interest. This present work proposes the use of a narrow-band transponder installed on a geostationary (GEO) satellite to be used as one anchor for a future time transfer. A channel calibration is made between the transceiver station and the chosen satellite. Diverse models are used to estimate the channel effects throughout the signal propagation path, estimate the time delay, and correct the measurements, accordingly. The available channel bandwidth on the proposed satellite is 2.7 kHz, limiting the accuracy of the time measurements. After integration of multiple pulses, a time accuracy of approximately 1 μs is obtained. The range measurements are compared against satellite positions propagated from publicly available two-line element sets (TLEs). The obtained results suggest that, after calibration, the expected accuracy and a good repeatability is obtained. Thus, making the QO-100 satellite a suitable anchor for the proposed technique.