Device synchronisation over a network

What is this patent about?

’761 is related to the field of synchronizing real-time clocks across separate devices in a distributed network. It specifically addresses the challenges of maintaining temporal alignment in multimedia applications, such as surround sound systems or video playback, where audio and video streams must be perfectly coordinated despite being processed by different hardware components. The background context highlights the difficulty of achieving this synchronicity when communication latencies are unknown or variable, particularly in wireless environments.

The underlying idea behind ’761 is the clever reuse of an existing low-level network heartbeat to calibrate high-level application clocks. Instead of attempting to transmit a real-time clock value directly—which would be rendered inaccurate by unpredictable transmission delays—the system anchors a specific real-time value to a specific, identifiable beat of a common time reference already used for network maintenance. By mapping a wall-clock time to a specific network slot or frame index, the receiver can reconstruct the correct time regardless of when the message actually arrives.

The claims of ’761 focus on a transceiver architecture and associated methods that utilize a shared time reference with distinguishable instances to synchronize clocks. The independent claims cover the mechanism of reading a real-time clock at a specific network instance and transmitting both that value and the identity of the instance. Conversely, they cover a receiver that uses this paired information to calculate a current real-time value by accounting for the elapsed intervals of the common reference between the identified instance and the present moment.

In a practical implementation, such as a Bluetooth piconet, the invention leverages the Link Level Synchronisation used for fast frequency hopping as the common time reference. The controller identifies a specific Bluetooth clock slot or frame number and associates it with the value of a separate Real Time Clock. Because the master and slave devices are already synchronized at the bit level to the frequency hopping sequence, they share a precise understanding of when each slot occurs, providing a sub-microsecond accurate framework for time distribution.

This approach differs from prior methods by decoupling the transmission latency from the synchronization accuracy. Traditional methods often suffer from jitter caused by protocol stack delays; however, by using distinguishable instances of a shared heartbeat, the ’761 invention ensures that the receiver can accurately 'back-date' or 'forward-date' the received time stamp to the correct network beat. This effectively eliminates the impact of variable network traffic or processing overhead, allowing distributed wireless speakers or displays to maintain perfect phase alignment.