MAC Unit Time Synchronization via Weighted Normalization
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Solution Overview
Problem
Existing wireless LAN time synchronization techniques face challenges in maintaining synchronization among STAs when AP failures occur or beacon packets are not received reliably, due to variations in time stamps from different APs and unstable links.
Innovation Solution
A wireless communication apparatus that includes a MAC unit capable of extracting and normalizing time information from multiple APs, weighting the normalized time information based on reception quality statistics to calculate a time correction value, and using this value to correct the local clock, ensuring stable time synchronization even during AP failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time synchronization is performed using beacon packets from multiple APs, then time synchronization accuracy is improved, but the system becomes vulnerable to AP failures and link instability
Solution Approach 1:
The patent changes the parameter of time stamp normalization by applying offset compensation to align time stamps from different APs to a common reference time. This allows multiple APs to contribute to synchronization without the harmful effect of absolute time differences, resolving the contradiction between using multiple APs for accuracy and vulnerability to failures.
Solution Approach 2:
The patent prepares compensation values for AP failures in advance by calculating offset values between the reference AP and other APs before failures occur. When an AP fails or becomes unstable, the STA can switch to using other APs with pre-calculated offset compensation, ensuring continuous reliable synchronization without being vulnerable to the failure.
2Stability of the object's composition
If the average value of time stamps from multiple APs is used for time synchronization, then time synchronization is maintained, but the absolute time variation among different APs causes inaccurate synchronization
Solution Approach 1:
Instead of using the raw average of time stamps, the patent transforms the parameter by normalizing each time stamp with its corresponding offset value before averaging. This parameter transformation eliminates the harmful absolute time variation among APs while preserving the beneficial continuity of synchronization.
3Quantity of substance
If beacon packets are received from unstable links, then more time information is available for synchronization, but the link instability reduces the reliability of received time stamps
Solution Approach 1:
The patent applies parameter transformation by normalizing time stamps from APs with different link qualities using their respective offset values. This allows time information from unstable links to be incorporated into synchronization while compensating for the reliability issues through the normalization process.
Solution Approach 2:
The system uses feedback from link quality measurements to dynamically adjust which APs are used for synchronization and how their time stamps are weighted. When links become unstable, the system can reduce reliance on those APs while still utilizing their time information with appropriate offset compensation.
Data Source
AI summary
According to an embodiment, a wireless communication unit includes a media access control (MAC) unit. The MAC unit includes a clock unit, an acquisition unit and a calculation unit. The clock unit includes a register which stores periodically counted-up first time information. The acquisition unit acquires a statistic for reception quality information on the received packet. The calculation unit normalizes the second time information, weights the normalized second time information using a time weight based on the statistic, and calculates a time correction value for correcting the first time information, using the weighted and normalized second time information. The time weight increases with increasing link stability indicated by the statistic.