Wireless Media Synchronization Using Master Clock and Phase Locked Loop
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Solution Overview
Problem
Existing wireless media networks face challenges in accurately synchronizing multiple audio and visual channels due to high latency and variable network conditions, leading to unwanted artifacts and difficulties in achieving precise time synchronization.
Innovation Solution
A method and apparatus that utilize a master device with a global clock to synchronize client devices' local clocks through beacon or probe response frames, adjusting their frequencies to match the master clock, and implementing a digital phase locked loop for phase synchronization, ensuring accurate time and phase synchronization across multiple playback units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NTP protocol timestamp method is used for time error measurement, then synchronization can be implemented, but measurement precision deteriorates due to large and variable wireless network latency
Solution Approach 1:
The patent introduces a dedicated time synchronization message structure that acts as an intermediary carrier, containing precise timestamp information from the master clock. This specialized message format enables accurate time transfer by separating synchronization data from regular audio data traffic, thus achieving microsecond-level precision despite wireless network variability.
Solution Approach 2:
The system implements a feedback mechanism where the slave device measures the actual time error based on received timestamps and sends this information back to the master device. The master device then adjusts its clock output based on this feedback, creating a closed-loop synchronization system that continuously optimizes timing accuracy.
2Measurement precision
If master clock independently synchronizes each slave device, then device complexity is reduced, but synchronization precision deteriorates due to lack of interaction between slaves
Solution Approach 1:
The master device serves as an intermediary that collects timing information from all slave devices and coordinates their synchronization. By having the master device manage the synchronization process centrally, the system achieves precise multi-device synchronization without requiring complex peer-to-peer interactions between slaves.
Solution Approach 2:
The patent combines multiple synchronization functions into a single master device that handles all slave devices. This merging of synchronization responsibilities into one central coordinator simplifies the overall network configuration while maintaining precise synchronization across all devices through unified time management.
3Measurement precision
If high stability crystal oscillators are used, then time error measurement improves, but cost and device complexity increase
Solution Approach 1:
The patent replaces the need for high-stability mechanical crystal oscillators with a software-based time synchronization system. By using timestamped messages and computational algorithms to track and correct time drift, the system achieves comparable synchronization precision without requiring expensive, complex hardware oscillators in each device.
Solution Approach 2:
The master device acts as an intermediary time reference that provides timing information to all slave devices. This allows slave devices to use simpler, less stable local oscillators while still achieving accurate synchronization by continuously referencing the master device's timestamps, thereby reducing hardware complexity and cost.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution achieves synchronization with an absolute time error of 20 microseconds, ensuring accurate and synchronized playback of multi-channel audio and visual content across multiple devices in a wireless network, improving the quality of media playback.
Implementation Method 1
One embodiment includes a phase locked loop in each slave device configured to follow the phase of the master's clock
Data Source
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AI summary
A method of keeping global time in a wireless network, the method comprising the steps of: using a first 802.11 chip set to read a Time Synchronization Function (TSF) to provide an initial time base; using an interconnected clock control circuit to read the TSF time directly from the 802.11 chip set and to implement a local clock based on time values read from the TSF function.