Slave Clock Synchronization Over Asymmetric Links
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Solution Overview
Problem
Existing methods for clock synchronization over links with asymmetric transmission rates, such as xDSL and GPON, face challenges due to packet delay variation and communication path asymmetries, which affect the accuracy of clock synchronization in small cell networks, particularly in indoor environments where GPS signals are unreliable and costly to maintain.
Innovation Solution
A method and system for synchronizing a slave clock with a master clock over networks with asymmetric transmission rates, involving the exchange of timing messages, recording timestamps, calculating relative transmission rates, and using filters like exponentially weighted moving average or Kalman filters to calculate skew and time offset, thereby compensating for delays and achieving accurate synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS-based synchronization is used in small cell networks, then clock synchronization accuracy is improved, but deployment cost and complexity increase significantly
Solution Approach 1:
The patent replaces expensive GPS receivers with standard clock devices that can be synchronized over existing broadband infrastructure. Instead of requiring specialized GPS equipment at each small cell, the system uses ordinary clocks that receive timing information through the broadband network, dramatically reducing hardware costs and deployment complexity while maintaining synchronization accuracy
Solution Approach 2:
The patent introduces a boundary clock or transparent clock in the broadband network that acts as an intermediary between the GPS reference clock and the small cell clocks. This intermediary distributes synchronized timing information through the existing broadband infrastructure, eliminating the need for direct GPS reception at each small cell while maintaining synchronization accuracy
2Ease of manufacture
If xDSL infrastructure is used for backhaul, then access cost is reduced, but transmission rate asymmetry causes synchronization accuracy to deteriorate
Solution Approach 1:
The patent explicitly addresses and compensates for the asymmetric transmission rates inherent in xDSL infrastructure. By measuring the different transmission rates in forward and reverse directions and applying appropriate compensation algorithms, the system maintains synchronization accuracy despite the asymmetric nature of the broadband connection
Solution Approach 2:
The patent implements feedback mechanisms where the system continuously monitors transmission delays and rate asymmetries in the xDSL connection, then adjusts synchronization parameters accordingly. This closed-loop approach compensates for the asymmetric transmission characteristics and maintains accurate clock synchronization over the cost-effective xDSL infrastructure
3Adaptability or versatility
If packet networks are used for time transfer, then infrastructure flexibility is improved, but packet delay variation causes synchronization precision to worsen
Solution Approach 1:
The patent performs preliminary measurements of packet delay characteristics and establishes compensation parameters before critical synchronization decisions are made. By pre-characterizing the packet network's delay behavior and storing compensation data, the system can quickly correct for packet delay variation without waiting for real-time measurements, maintaining high synchronization precision despite the inherent variability of packet networks
Solution Approach 2:
The patent implements dynamic compensation mechanisms that continuously adapt to changing packet delay conditions. The system adjusts synchronization parameters in real-time based on current packet delay measurements, allowing it to maintain accuracy even as network conditions vary. This dynamic approach enables the system to handle the inherent variability of packet networks while preserving synchronization precision
Data Source
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AI summary
This invention relates to methods and devices for clock synchronization. The invention has particular application in the alignment of slave clocks to a master clock and in dealing with transmission delay asymmetries where the forward and reverse communication paths between the master and slave clocks have asymmetric transmission rates. Such methods and devices have particular application in small cell backhaul solutions for 4G/LTE deployments. In embodiments of the invention, the slave clock uses link rate information to estimate the transmission delay asymmetry and thus estimate the offset and skew of the slave clock. Embodiments provide a simple linear approximation technique and a Kalman filter-based technique for estimating offset and skew of the slave clock.