Communication Apparatus Asymmetrical Delay Compensation
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Solution Overview
Problem
Time synchronization becomes indefinite in transmission systems with asymmetrical delay characteristics, where transmission delay times differ based on the direction of transmission, leading to instability and the need for expensive frequency sources to maintain synchronization.
Innovation Solution
A communication apparatus and method that store difference information between time information received from a synchronization source and time information from a separate origin, allowing for time synchronization using this stored difference information when the secondary time information is unavailable, thereby maintaining synchronization accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GNSS is used for time synchronization, then time synchronization accuracy is improved, but fault-tolerance deteriorates due to susceptibility to signal blockage and interference
Solution Approach 1:
The patent introduces a packet network as an intermediary time synchronization system that works alongside GNSS. When GNSS signals are blocked or interfered with, the packet network serves as a backup synchronization path, maintaining fault-tolerance while preserving time synchronization accuracy through dual-path redundancy
2Stability of the object's composition
If expensive frequency sources like OCXO or atomic oscillators are used to maintain time synchronization during Holdover situation, then time synchronization stability is improved, but cost deteriorates
Solution Approach 1:
The patent performs preliminary calibration of transmission delay characteristics during normal GNSS operation. The delay difference information is stored in advance in a storage unit, so when Holdover situation occurs and GNSS signal is lost, the pre-stored calibration data can be immediately applied without requiring expensive frequency sources, thus maintaining stability while reducing cost
3Ease of manufacture
If IEEE 1588 system is superimposed on transmission system for time synchronization, then cost is reduced, but time synchronization accuracy deteriorates due to asymmetrical delay characteristics
Solution Approach 1:
The patent applies local quality by specifically addressing the asymmetrical delay characteristic of the transmission path. Instead of treating all transmission delays uniformly, the system measures and compensates for the specific delay difference between forward and reverse directions in the transmission path, thereby maintaining IEEE 1588 cost-effectiveness while improving synchronization accuracy
4Reliability
If average arrival time or shortest arrival time is used to correct delay fluctuation, then some delay variation is reduced, but time synchronization accuracy deteriorates when bi-directional delays are different
Solution Approach 1:
The patent performs preliminary measurement and storage of the delay difference between forward and reverse transmission directions during normal operation. This pre-calibrated asymmetry information is stored and later used to correct synchronization calculations, allowing the system to maintain both fluctuation resistance and accuracy by compensating for known asymmetrical delays
Data Source
AI summary
A communication apparatus (13) according to the present invention is provided with: a storage unit (131) that stored in advance difference information (1311), which is the difference between first time information (t1) and second time information (t2), said first time information (t1) being received from a synchronization source communication apparatus (11) as a time synchronization source connected to a transmission system (12) wherein transmission delay time is different depending on the direction of transmission, and said second time information (t2) obtained from a time synchronization origin (14) other than the transmission system (12); and a time synchronization means (132) that carries out, when the second time information (t2) cannot be obtained from the time synchronization origin (14), time synchronization with the synchronization source communication apparatus (11) using the difference information (1311) read out from the storage unit (131).