Wireless Station Clock Synchronization for Accurate Media Playback
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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, especially in applications requiring high accuracy like left/right stereo channel synchronization.
Innovation Solution
Utilizing the physical layer clock in wireless stations, synchronized with the access point's timing beacon, to correct the station's free-running clock, combined with NTP for precise time synchronization, ensuring all stations are accurately aligned.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NTP protocol is used for time synchronization in wireless networks, then time synchronization can be achieved, but accuracy deteriorates due to asymmetric receive and transmit paths
Solution Approach 1:
The patent introduces a timestamp mechanism as an intermediary to measure and compensate for the asymmetric path delays. By recording timestamps at both transmit and receive ends and calculating the difference, the system can identify and correct for the asymmetric delays that NTP alone cannot handle, thereby improving both accuracy and reliability of time synchronization.
Solution Approach 2:
The patent replaces the purely software-based NTP time synchronization mechanism with a hybrid approach that incorporates hardware-level timestamping at the physical layer. This substitution of mechanical/hardware timing mechanisms provides more precise and reliable time measurements, overcoming the limitations of software-based NTP in wireless asymmetric environments.
2Device complexity
If free running clocks are used in each station, then device complexity is reduced, but time synchronization precision deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where stations exchange timestamp information and calculate clock drift based on the difference between their free running clock and the received timestamps. This feedback loop allows each station to adjust its clock offset dynamically, achieving high precision time synchronization while maintaining the simplicity of free running clocks without requiring complex synchronized clock circuits.
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.