Skew Estimation Using Levenberg-Marquardt Algorithm
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Solution Overview
Problem
Current time synchronization methods, such as those using the IEEE 1588 PTP, face challenges in accurately estimating clock skew between master and slave clocks due to asymmetric communication paths and variable queuing delays, leading to slow convergence of estimation algorithms like the Kalman filter.
Innovation Solution
A method employing a least squares fitting algorithm, specifically the Levenberg-Marquardt algorithm, is used to quickly generate an initial accurate skew estimate by exchanging timing messages and timestamps between the master and slave clocks, minimizing a cost function to normalize phase offsets and achieve a zero skew state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional time synchronization algorithms like Kalman filter are used to estimate clock skew, then accurate time synchronization can be achieved, but the convergence time is too long
Solution Approach 1:
The patent applies preliminary action by performing a least squares fitting to obtain an initial skew estimate before the Kalman filter begins its iterative process. This preliminary estimation provides a head start, allowing the system to converge to accurate time synchronization much faster than using Kalman filter alone, directly resolving the contradiction between accuracy and convergence time
Solution Approach 2:
The patent introduces an intermediary approach by combining two estimation methods: least squares fitting for initial rapid estimation and Kalman filter for continuous refined estimation. This intermediary least squares step acts as a bridge that accelerates the overall convergence while maintaining the accuracy benefits of the Kalman filter, solving the time-loss problem without sacrificing measurement precision
2Device complexity
If path delay estimation assumes symmetric communication paths, then calculation is simplified, but accuracy deteriorates due to asymmetric forward and reverse delays
Solution Approach 1:
The patent directly addresses asymmetric communication paths by using separate forward path delay (df) and reverse path delay (dr) estimates in the skew calculation formula. Instead of assuming df = dr, the invention explicitly models the asymmetry, thereby improving measurement precision while managing calculation complexity through efficient estimation algorithms
Solution Approach 2:
The patent changes the parameter representation by introducing distinct forward and reverse delay parameters (df and dr) rather than using a single average delay. This parameter change allows the system to accurately capture asymmetric path characteristics while the least squares fitting efficiently manages the increased computational requirements
Data Source
AI summary
This invention relates to methods and systems for estimating skew based on, for example, the IEEE 1588 Precision Time Protocol (PTP). These methods and systems can allow the clock skew between a master clock (server) and slave clock (client) exchanging PTP messages over a packet network to be estimated more rapidly than conventional estimation techniques and thereby improve the convergence of standard estimation algorithms. In one embodiment, the skew estimation is derived from a set of timestamps from a message exchange between the master and slave using a non-linear least square-fitting algorithm. An example of the fitting algorithm is the Levenberg-Marquardt algorithm.