Grandmaster Clock Synchronization for GPS-Free TDMA Modems
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Solution Overview
Problem
Existing satellite communication systems face challenges in accurately synchronizing clock timing and frequency for efficient TDMA-based communication, particularly in the absence of a GPS external reference signal, leading to inefficiencies and errors.
Innovation Solution
A communication system utilizing a grandmaster clock and modem unit with network and master clocks, along with a marker generator, to synchronize frequency and time with high accuracy to a GPS reference, enabling reliable operation even without a GPS signal, and allowing low aperture size and high bits/Hz efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system uses GPS external reference signal for clock synchronization, then frequency and time synchronization accuracy is improved, but the system reliability deteriorates when GPS signal is unavailable
Solution Approach 1:
The patent introduces a grandmaster clock as an intermediary component that receives GPS reference signals and distributes synchronized clock signals to multiple modem units. This mediator architecture allows the system to maintain high synchronization accuracy through the grandmaster clock while providing backup local oscillators in each modem unit to ensure continued operation when GPS signals are unavailable, thus resolving the contradiction between accuracy and reliability.
Solution Approach 2:
The system performs preliminary synchronization by having the grandmaster clock pre-process GPS reference signals and distribute synchronized clock references to all modem units before communication operations begin. Each modem unit also prepares backup local oscillators in advance. This preliminary action ensures that when GPS signals become unavailable, the system can immediately switch to local backups without losing synchronization accuracy or operational reliability.
2Adaptability or versatility
If the system operates without GPS reference signal, then system adaptability is improved, but frequency synchronization accuracy deteriorates
Solution Approach 1:
The grandmaster clock serves as an intermediary that maintains the master reference clock even when GPS signals are unavailable, using backup mechanisms. This intermediary preserves frequency synchronization accuracy for the entire system while allowing individual modem units to operate independently without GPS, thus achieving both adaptability and precision.
Solution Approach 2:
The system implements beforehand cushioning by providing backup local oscillators and reference signals in each modem unit and at the grandmaster clock. These backup mechanisms are prepared in advance to cushion against GPS signal unavailability, ensuring that frequency synchronization accuracy is maintained even when the primary GPS reference is lost, while simultaneously enabling operation in GPS-denied environments.
3Measurement precision
If the system uses separate network clock and master clock, then frequency and time synchronization are improved, but device complexity increases
Solution Approach 1:
The patent segments the clock synchronization function into two distinct components: a network clock for time reference and a master clock for frequency reference. This segmentation allows each clock to be optimized for its specific function, improving overall synchronization accuracy. The grandmaster clock architecture further segments the system into a central synchronization source and distributed modem units, managing complexity through modular design while maintaining high precision.
Data Source
AI summary
Communication systems and methods are disclosed herein. In an embodiment, a modem unit for a communication system includes a marker generator, a network clock and a master clock. The marker generator is configured to (i) derive a time reference from a time reference signal, (ii) derive a frequency reference from a first frequency reference signal, and (iii) communicate with a remote terminal using the time reference and the frequency reference. The network clock is configured to (i) derive a clock frequency from a second frequency reference signal and (ii) output the time reference signal to the marker generator. The master clock is configured to (i) output the first frequency reference signal to the marker generator and (ii) output the second frequency reference signal to the network clock.