Wireless Network Time Synchronization Using TSF Beacons
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Solution Overview
Problem
Existing time synchronization protocols like NTP in wireless networks, such as IEEE 802.11 Wi-Fi, suffer from inaccuracies due to asymmetric receive and transmit paths, leading to unsynchronized playback of media across stations, particularly in applications requiring high accuracy like left/right stereo channel synchronization.
Innovation Solution
Implement a method where each wireless station synchronizes its operating system clock using a physical layer clock at the access point, utilizing the timing beacon (TSF) to correct and align the station's free-running clock with the access point's clock, and integrate this with NTP for precise synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NTP protocol is used for time synchronization in wireless networks, then time synchronization is provided, but synchronization accuracy deteriorates due to asymmetric receive and transmit paths
Solution Approach 1:
The patent introduces a timing beacon (TSF) from the physical layer as an intermediary time reference that mediates between the asymmetric wireless paths and the NTP protocol. The TSF provides a common reference point that both stations can use to calculate their respective clock offsets, eliminating the need to rely solely on the asymmetric NTP paths for accuracy.
Solution Approach 2:
The patent segments the time synchronization function into two parts: (1) physical layer clock synchronization using timing beacons for high-precision short-term synchronization, and (2) application layer NTP for long-term timekeeping. This segmentation allows each layer to optimize for its specific requirements, with the physical layer handling the asymmetric path issues and the application layer maintaining overall time accuracy.
2Device complexity
If free running clocks are used in each station, then device complexity is reduced, but clock synchronization deteriorates due to clock drift between stations
Solution Approach 1:
The patent implements feedback by having each station continuously monitor the difference between its free-running clock and the reference station's clock via timing beacons. This feedback information is used to adjust the local clock frequency, creating a closed-loop synchronization system that maintains accuracy without requiring complex hardware.
Solution Approach 2:
The patent changes the operating parameters of the free-running clocks by dynamically adjusting their frequency based on the measured offset from the reference clock. Instead of using fixed-frequency oscillators, the system varies the clock parameters (frequency) to maintain synchronization, allowing simple hardware to achieve high precision.
Data Source
AI summary
A wireless media distribution system is provided comprising an access point (6) for broadcasting media and a plurality of stations (2) for reception and playback of media. Each station is configured for receiving and decoding a timestamp in a beacon frame transmitted repeatedly from the access point. This is used to control the output signal of a station physical layer clock (12) which is then used as a clock source for an application layer time synchronisation protocol. This application layer time synchronisation protocol can then be used in the station to control an operating system clock (8) for regulating playback of media.