Clock Synchronization Over Asymmetric Links
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing broadband infrastructure, such as xDSL and GPON, faces challenges in achieving accurate clock synchronization due to inherent transmission rate asymmetries, which complicate the synchronization of small cell base stations in mobile telecommunications networks.
Innovation Solution
A method and system that synchronize a slave clock with a master clock by exchanging timing messages, recording timestamps, calculating relative transmission rates, and adjusting for skew and offset to compensate for transmission rate asymmetries, using techniques like exponentially weighted moving average filters or Kalman filters to improve synchronization accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If existing broadband infrastructure (xDSL, GPON) is used for clock synchronization, then deployment cost is reduced and accessibility is improved, but transmission rate asymmetries cause synchronization accuracy to deteriorate
Solution Approach 1:
The patent explicitly addresses transmission rate asymmetry by introducing separate forward and reverse rate parameters (Rf and Rr). The system models the asymmetric transmission characteristics of xDSL and GPON networks, where downstream and upstream rates differ significantly. This asymmetry is incorporated into the clock synchronization algorithm to compensate for the resulting timing errors.
Solution Approach 2:
The patent changes the synchronization parameters by introducing rate compensation factors based on measured forward and reverse transmission rates. The algorithm dynamically adjusts timing calculations using these rate parameters, transforming the synchronization approach from assuming symmetric rates to actively compensating for asymmetric rates through parameter modification.
2Device complexity
If traditional symmetric rate assumptions are used in clock synchronization, then algorithm complexity is reduced, but synchronization accuracy deteriorates due to transmission rate asymmetries
Solution Approach 1:
The patent implements feedback by measuring actual forward and reverse transmission rates and using these measurements to adjust synchronization calculations. The system continuously monitors transmission characteristics and feeds this information back into the clock synchronization algorithm, allowing dynamic adaptation to network conditions without requiring overly complex pre-computed models.
Solution Approach 2:
The patent performs preliminary rate measurement and characterization before executing the main synchronization protocol. By pre-determining the forward and reverse transmission rates and storing them as compensation parameters, the system prepares the necessary correction factors in advance, simplifying the real-time synchronization calculations while maintaining high accuracy.
Data Source
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.