US-20260126512-A1 - ANTENNA SYSTEMS AND METHODS FOR TRACKING NON-GEOSYNCHRONOUS SATELLITES

Abstract

A method performed by a ground station antenna system for tracking a non-Geo satellite. A signal is received from the satellite and a signal quality metric associated with the signal is estimated. A first tracking mode is selected and implemented when the estimated signal quality metric is below a threshold, in which the signal is demodulated to obtain demodulated signal quality metric (DSQM) estimates, and then a first tracking operation is performed to point an antenna beam at the satellite based on the DSQM estimates. A second tracking mode is selected and implemented when the estimated signal quality metric is above the threshold, in which signal strength estimates of the signal are obtained and then a second tracking operation is performed to point the antenna beam at the satellite based at least in part on the signal strength estimates.

Inventors

• Rodney A. Morris
• Patrick E. TYNAN
• DAVID E. SINYARD

Assignees

• VIASAT, INC.

Dates

Publication Date

20260507

Application Date

20250808

Claims (1)

1. 1 . A method performed by a ground station antenna system, for tracking a non-geosynchronous earth orbit (non-Geo) satellite, comprising: receiving a signal from the non-Geo satellite; estimating a signal quality metric associated with the signal; selecting and implementing a first tracking mode when the estimated signal quality metric is below a threshold; in the first tracking mode, demodulating the signal and obtaining demodulated signal quality metric (DSQM) estimates, then performing a first tracking operation to point an antenna beam at the satellite based on the DSQM estimates; and selecting and implementing a second tracking mode when the estimated signal quality metric is above the threshold.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is related to and claims priority under 35 U.S.C. 120 to U.S. patent application Ser. No. 17/998,450, filed in the United States Patent and Trademark Office on Nov. 10, 2022, which is a 371 National Stage entry of PCT application no. PCT/US2021/032,307, filed May 13, 2021, entitled ANTENNA SYSTEMS AND METHODS FOR TRACKING NON-GEOSYNCHRONOUS SATELLITES, which claims the benefit of priority to U.S. Provisional Application No. 63/024,504 filed on May 13, 2020, entitled SYSTEMS AND METHODS FOR TRACKING LEO SATELLITES, the entire contents of each of which are incorporated by reference herein. TECHNICAL FIELD This disclosure relates generally to satellite communications and more particularly to ground based antenna systems and methods for tracking non-geosynchronous earth orbit (non-Geo) satellites. DISCUSSION OF RELATED ART Non-Geo satellites include low earth orbit (Leo) satellites, which orbit up to about 2,000 km above earth, and medium earth orbit (Meo) satellites, which orbit between about 2,000 km and 35,000 km above earth. Throughout the day, a non-Geo satellite moves across fixed ground locations around the globe, often quite rapidly. For instance, a ground station antenna (e.g., a gateway antenna) may communicate with any given satellite for only up to 15 minutes, i.e., the time the satellite moves from horizon to horizon across the antenna's field of view. Thus, a constellation of non-Geo satellites may act in concert to enable continuous communications with a ground station via handover from one satellite to the next. As a non-Geo satellite traverses the sky and communicates with a ground station, the ground station may track the position of the satellite and adjust the direction of its beam peak to point at the satellite and thereby optimize communication signal quality. Example tracking methods for the tracking include “program tracking”, which does not require signal strength measurement data for beam adjustments, and “autotracking”, which does rely on signal strength measurement data. With program tracking, a path of the satellite is predicted based on satellite information provided to/calculated by the ground station, and the beam peak is adjusted to follow the predicted path. Autotracking techniques, such as monopulse tracking and mispointing correction methods, allow the system to accurately point at the satellite by compensating for errors in the satellite's path and/or in the system alignment. Monopulse tracking typically involves receiving the satellite signal with fixed auxiliary antennas and determining the signal direction by adding and subtracting the received signals from the auxiliary antennas. Mispointing correction methods involve periodically mispointing the peak direction of a main antenna's beam and measuring receive signal strength or quality for each mispointed condition to arrive at an optimized peak direction. Some examples of mispointing correction methods include “hill climbing”, in which subsequent test directions in the process depend on a current test direction result, and conical scanning, in which a mispointing test sequence follows a predetermined conical path with respect to a starting direction. SUMMARY An aspect of the present disclosure relates to a method performed by a ground station antenna system for tracking a non-Geo satellite. In the method, a signal is received from the satellite and a signal quality metric (SQM) associated with the signal is estimated. A first tracking mode is selected and implemented when the estimated SQM is below a threshold. In the first tracking mode, the signal is demodulated and demodulated signal quality metric (DSQM) estimates are obtained; then a first tracking operation is performed to point an antenna beam at the satellite based on the DSQM estimates. A second tracking mode is selected and implemented when the estimated SQM is above the threshold. In the second tracking mode, signal strength estimates of the signal are obtained via a measurement device. A second tracking operation is then performed to point the antenna beam at the satellite based at least in part on the signal strength estimates. The DSQM based tracking is more accurate and reliable for low quality signals as compared to signal strength based tracking. On the other hand, when received signal strength and quality is high, signal strength based tracking may be superior. Accordingly, methods of the present disclosure may optimize tracking performance throughout the non-Geo satellite's path with respect to the ground station antenna, and may increase the range for which signal communication with requisite quality is feasible. An example of the signal quality metric (SQM) is signal to noise ratio (SNR), which may be estimated through direct measurement by the antenna system. Alternatively, the SNR is estimated as a value corresponding to a predicted elevation position of the satellite in accordance with epheme