Satellite Repeater Timing Holdover 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, 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 to predict and adjust the frequency of the local signal, maintaining synchronization through feedback loops and slewing control, even during GPS signal interruptions, by generating predicted control words based on historical data and using a linear curve fit to ensure accurate timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If expensive rubidium-based local oscillators are used to achieve Stratum level 2 timing accuracy, then timing accuracy is improved, but system cost increases
Solution Approach 1:
The patent replaces expensive rubidium-based local oscillators with lower-cost oscillators (such as OCXO or TCXO) that have shorter term stability characteristics. By combining these cheaper oscillators with GPS discipline and prediction algorithms, the system achieves Stratum level 2 timing accuracy without the high cost of rubidium standards.
Solution Approach 2:
The patent implements prediction algorithms that use historical timing data and control words to forecast future timing behavior. This preliminary action allows the system to compensate for oscillator drift and maintain accuracy during GPS outages, reducing the need for expensive hardware with inherently better long-term stability.
2Measurement precision
If GPS signal reception is maintained continuously, then timing accuracy is improved, but system reliability deteriorates in dense urban areas where GPS signals are intermittently lost
Solution Approach 1:
The patent implements prediction algorithms and holdover capabilities that prepare the system in advance for potential GPS outages. By continuously analyzing timing trends and storing historical control words, the system builds a buffer of predictive information that allows it to maintain accuracy during signal interruptions without degrading overall reliability.
Solution Approach 2:
The patent employs feedback mechanisms where the system continuously monitors GPS signal quality and timing performance. When signal degradation is detected, the system transitions to prediction-based holdover mode, using feedback from historical data to maintain timing accuracy. This adaptive feedback loop ensures reliability by automatically switching between GPS-disciplined and prediction-based operation.
3Reliability
If the system transitions to holdover mode during GPS outages, then reliability is improved, but timing accuracy may deteriorate over extended periods
Solution Approach 1:
The patent implements prediction algorithms that continuously prepare holdover capability by analyzing historical timing data and oscillator characteristics before GPS outages occur. This preliminary characterization allows the system to make accurate predictions during outages, maintaining timing precision even when operating in holdover mode for extended periods.
Solution Approach 2:
The patent employs dynamic prediction models that adapt to changing oscillator behavior and environmental conditions. The prediction algorithm adjusts its parameters based on real-time performance data, allowing the system to maintain accuracy during holdover mode by dynamically compensating for drift and environmental effects that would otherwise degrade timing precision.
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.