BLE Reference Clock Synchronization With Drift Compensation
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Solution Overview
Problem
The Bluetooth Low Energy (BLE) protocol lacks a stable, long-term time synchronization mechanism due to unknown travel times of data packets and internal clock inaccuracies, leading to uncertainties in timestamping and data integrity across wireless networks.
Innovation Solution
A method involving initial synchronization with a central device reference clock, followed by periodic callback messages to adjust for clock drift, allowing precise calculation of travel times and synchronization of peripheral devices with the central device clock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency hopping and retry mechanisms are applied to avoid congestion and ensure reliable transmission, then transmission reliability is improved, but travel time uncertainty increases
Solution Approach 1:
The patent applies preliminary action by establishing an initial time synchronization between peripheral and central devices before actual data transmission occurs. This initial synchronization prepares the system with known timing relationships, enabling subsequent calculation of travel times even when frequency hopping and retries introduce delays. The synchronization happens in advance, creating a reference framework that persists through the unreliable transmission process.
2Use of energy by moving object
If connection intervals with transmission windows are used to manage bandwidth, then energy consumption is reduced, but long-term time synchronization stability deteriorates
Solution Approach 1:
The patent implements feedback by having the peripheral device calculate the actual travel time of callback messages based on the initial synchronization reference and the known connection interval timing. This calculated travel time information is fed back into the system to compensate for clock drift between devices. The feedback mechanism continuously corrects the time synchronization, maintaining stability despite the intermittent connection intervals that save energy.
3Measurement precision
If initial time synchronization is performed based on established connection, then initial synchronization accuracy is improved, but long-term drift compensation capability deteriorates
Solution Approach 1:
The patent applies periodic action by utilizing the regular connection intervals inherent in BLE communication to periodically exchange callback messages between central and peripheral devices. Each callback message provides an opportunity to measure and compensate for time drift. This periodic reinforcement of the synchronization, occurring at each connection interval, extends the effective duration of accurate time synchronization far beyond what a single initial synchronization could achieve alone.
Data Source
AI summary
Reference clock time synchronization in a wireless network via a connection time synchronization based on an established connection to a central device, a callback message for time synchronization from the central device at a start and/or an end of a connection interval, where the callback message includes a central device reference time, calculating connection intervals elapsed between sending the callback message by the central device and receiving the callback message by the peripheral device represented by a recorded local peripheral device reference time, determining a current time drift between the received central device reference time and the recorded local peripheral device reference time based on the calculated number of connection intervals, and adjusting the peripheral device reference time based on a time offset according to the connection time synchronization and based on the determined time drift to synchronize with the central device local reference clock.