Clock Offset and Skew Estimation via Linear Programming
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Solution Overview
Problem
Existing methods for time synchronization in small cell networks, particularly those using IEEE 1588 PTP, face challenges in accurately accounting for transmission rate asymmetry and communication path asymmetries, leading to errors in clock recovery due to dissimilar forward and reverse path delays, which are exacerbated by the inherent asymmetries in DSL and GPON technologies.
Innovation Solution
A slave device connected to a master device over a network, equipped with a processor that exchanges timing messages, records timestamps, and formulates a linear programming problem to estimate the skew and offset of the slave clock relative to the master clock, taking into account the relationship between forward and reverse transmission speeds, thereby synchronizing the slave clock to the master clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional time synchronization methods (IEEE 1588 PTP) are used in small cell networks, then clock synchronization can be achieved, but transmission rate asymmetry and communication path asymmetries cause errors in clock recovery
Solution Approach 1:
The patent applies asymmetry by formulating a linear programming problem that explicitly accounts for asymmetric transmission rates and communication path delays between master and slave devices. Instead of assuming symmetric paths, the invention models the asymmetric nature of DSL and GPON networks, using separate forward and reverse transmission speed variables to accurately represent the asymmetric conditions and achieve precise clock recovery despite the asymmetry
Solution Approach 2:
The invention changes parameters by introducing variables representing the relationship between forward and reverse transmission speeds into the synchronization calculation. The linear programming formulation dynamically adjusts for transmission rate asymmetry by treating transmission speeds as variables to be estimated rather than fixed symmetric values, thereby adapting the synchronization process to the actual asymmetric network conditions
2Measurement precision
If GPS receivers and antennas are installed at every small cell base station, then accurate time reference can be obtained, but capital expenditure and operational expenditure increase significantly
Solution Approach 1:
The patent applies copying by creating a virtual time reference at slave devices through calculation rather than physical GPS receivers. The slave device copies the master clock's time reference by exchanging timing messages and calculating offset and skew, eliminating the need for physical GPS infrastructure at each small cell while achieving equivalent synchronization accuracy
Solution Approach 2:
The invention extracts the time reference function from physical GPS receivers and implements it through software-based clock synchronization algorithms. By taking out the GPS dependency and replacing it with network-based time transfer using linear programming, the solution eliminates expensive hardware while maintaining synchronization capabilities
3Device complexity
If transmission rate asymmetry is not accounted for in time synchronization, then calculation complexity is reduced, but clock recovery accuracy deteriorates due to dissimilar forward and reverse path delays
Solution Approach 1:
The patent applies preliminary action by formulating the linear programming problem that incorporates transmission rate asymmetry before performing clock synchronization. The asymmetric transmission characteristics are modeled in advance with appropriate constraints and variables, allowing the synchronization algorithm to pre-compensate for the expected delays rather than attempting to correct them after the fact
Data Source
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.