GPS Repeater Synchronization Using PLL Holdover Prediction
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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, especially 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 local 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, and utilizing a linear curve fit for long-term stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If expensive rubidium-based oscillators are used to maintain Stratum level 2 timing accuracy, then timing accuracy is improved, but cost increases
Solution Approach 1:
The patent replaces expensive rubidium-based oscillators with lower-cost oscillators that can maintain timing accuracy for shorter durations. The system uses prediction algorithms to generate control words that compensate for oscillator drift during GPS signal outages, enabling the use of economical oscillators while maintaining Stratum level 2 timing accuracy throughout the required holdover period.
Solution Approach 2:
The system performs preliminary characterization of oscillator behavior during normal GPS-operational conditions. By analyzing historical control words and oscillator drift patterns before GPS signal loss occurs, the prediction algorithm pre-computes compensation parameters that are applied during outages, allowing accurate timing maintenance without expensive hardware.
2Measurement precision
If GPS signal reception is lost in dense urban areas, then signal quality degradation occurs, but the system must maintain timing accuracy
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors GPS signal availability and oscillator performance. During GPS outages, the prediction algorithm uses historical control word data to generate real-time compensation control words that are fed back to the oscillator, closing the timing control loop even without external GPS reference signals.
Solution Approach 2:
The system prepares for potential GPS signal loss by maintaining a history of control words and characterizing oscillator drift behavior in advance. When signal loss occurs in dense urban areas, this pre-collected data serves as a cushion that enables the prediction algorithm to generate accurate control words immediately, preventing timing accuracy degradation during the outage.
3Measurement precision
If the duration of GPS signal loss increases, then maintaining timing accuracy becomes more difficult, but Stratum level 2 accuracy must be sustained
Solution Approach 1:
The system performs comprehensive oscillator characterization and control word generation during normal operational periods before GPS signal loss occurs. By accumulating historical data on oscillator drift patterns and control word adjustments, the system builds a predictive model that remains valid throughout extended outages, enabling maintenance of Stratum level 2 timing accuracy regardless of the duration of GPS signal loss.
Solution Approach 2:
The prediction algorithm enables the oscillator system to self-correct during GPS outages by generating control words autonomously based on its own historical performance data. The system serves itself by using its past behavior patterns to compensate for current drift, eliminating the need for external reference signals during extended periods of GPS unavailability.
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.