GPS Repeater Synchronization Using Predicted PLL Control Words
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Solution Overview
Problem
Terrestrial repeaters in satellite signal delivery systems face challenges in maintaining timing accuracy during intermittent loss of GPS signal reception, particularly in dense urban areas where GPS signals are degraded, leading to potential signal quality degradation and the need for cost-effective solutions that can achieve Stratum level 2 timing accuracy without relying on expensive rubidium-based oscillators.
Innovation Solution
A method and system for synchronizing a local reference signal with a GPS signal using control words generated based on timing offsets, allowing for predicted adjustments to maintain synchronization even during GPS signal interruptions, employing a feedback path and frequency adjustments to ensure accurate timing, including the use of a linear curve fit for long-term stability and a second-order estimate for rapid lock-on strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS signal reception is used for timing synchronization, then timing accuracy is improved, but signal reliability deteriorates in dense urban areas with intermittent GPS loss
Solution Approach 1:
The system pre-characterizes the local oscillator's drift behavior by collecting timing offset data during periods when GPS signals are available. This preliminary characterization creates a predictive model that can be applied during GPS outages to maintain timing accuracy without real-time GPS input.
Solution Approach 2:
Instead of directly using expensive Stratum 2 rubidium oscillators, the system creates a virtual copy of their performance by using a combination of a cheaper Stratum 3 oscillator and a predictive algorithm that replicates the timing stability characteristics of higher-grade oscillators during GPS outages.
2Measurement precision
If Stratum level 2 timing accuracy is achieved using rubidium-based oscillators, then timing precision is improved, but system cost increases significantly
Solution Approach 1:
The system replaces expensive, long-lived rubidium oscillators with a combination of a cheaper crystal oscillator and a computational prediction mechanism. The cheaper oscillator is compensated algorithmically to achieve equivalent timing performance, eliminating the need for expensive hardware.
Solution Approach 2:
The system changes the operational parameters of a Stratum 3 oscillator through predictive control, adjusting its output based on pre-characterized drift patterns. This parameter adjustment allows a lower-grade oscillator to achieve Stratum 2 equivalent performance during GPS outages.
3Stability of the object's composition
If GPS signal loss compensation is implemented, then timing stability is improved during outages, but system complexity increases
Solution Approach 1:
The system replaces complex hardware-based timing stabilization mechanisms with a software-based predictive algorithm. Instead of using additional physical components or complex feedback hardware, the solution uses computational prediction to maintain timing stability, reducing overall system complexity.
Data Source
AI summary
Systems and methods for maintaining synchronization of repeater networks with Global Positioning System (GPS) signals using phase locked loops (PLLs) and based on generation of predicted control words for controlling local oscillator frequencies is described. The predicted control words can be generated based on performing a linear fit of control words generated over a predetermined duration of time. Phase locked loops with additional false GPS pulse identification and GPS signal loss compensation circuitry can enforce a false pulse count threshold and/or an error threshold. The additional circuitry and prediction of control words can overcome errors in GPS receiver outputs and maintain accuracy of signal timings across single frequency networks using inexpensive local oscillators.