Linear Programming Clock Offset Estimation for Asymmetric Networks
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Solution Overview
Problem
Existing methods for time synchronization in small cell networks, particularly those using DSL or GPON, face challenges due to transmission rate asymmetry and communication path asymmetries, which affect the accuracy of clock recovery and synchronization, especially in environments where GPS signals are inaccessible or impractical.
Innovation Solution
A slave device connected to a master device over a network uses linear programming to estimate and correct for transmission rate asymmetry and other communication path asymmetries by exchanging timing messages and solving for clock offset and skew, allowing for accurate synchronization without requiring knowledge of measurement and process noise statistics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS receivers and antennas are installed at every small cell base station, then clock synchronization accuracy is improved, but capital expenditure and operational complexity increase
Solution Approach 1:
The patent introduces an intermediary system consisting of a master clock and slave clocks that communicate through timing messages over the network. Instead of each small cell independently acquiring GPS signals, a hierarchical time distribution system is established where timing information is propagated from master to slave clocks through the existing network infrastructure, eliminating the need for GPS receivers at each small cell.
Solution Approach 2:
The patent creates a replicated time reference system where slave clocks copy and synchronize to the master clock's time signal. Multiple slave clocks can be distributed throughout the network, each maintaining a copy of the master time reference, thereby providing synchronized timing without requiring physical GPS receivers at each location.
2Measurement precision
If transmission rate asymmetry is compensated using traditional methods, then synchronization accuracy is improved, but measurement and process noise statistics must be known, increasing system complexity
Solution Approach 1:
The system performs self-characterization by having the master and slave clocks exchange timing messages and automatically measure their own transmission rates and delays. The slave clock determines the forward and reverse transmission rates by comparing timestamps from exchanged messages, and uses these self-measured parameters to compensate for asymmetry without requiring external calibration or knowledge of noise statistics.
Solution Approach 2:
The patent performs preliminary characterization of the transmission path by measuring forward and reverse transmission rates before using them for time synchronization. The system pre-calculates compensation factors based on measured asymmetry, which are then applied to correct timing offsets, thereby preparing the system in advance for accurate synchronization without requiring real-time knowledge of noise characteristics.
3Measurement precision
If linear programming is used to estimate offset and skew, then synchronization accuracy is improved, but computational processing time increases
Solution Approach 1:
The patent applies linear programming to estimate clock offset and skew from a selected subset of timing message exchanges rather than processing all available data continuously. By using partial data sets or sampling approaches, the system achieves sufficient estimation accuracy without the computational burden of processing every timestamp, thereby balancing precision with processing time requirements.
Data Source
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AI summary
This invention relates to methods and systems for estimating offset and skew using linear programming. Embodiments of the invention relate to methods and systems which apply linear programming principles to links with asymmetric transmission rates which are estimated from an exchange of timing messages (for example under IEEE 1588 PTP). Further embodiments provide for the estimation of clock offsets using linear programming techniques when the skew is known or estimated.