Wearable Clock Synchronization Using Cardiac Activity Signals
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Solution Overview
Problem
Existing methods for synchronizing accelerometer-based metrics from wrist-worn wearables, such as those used for monitoring atopic dermatitis, face challenges due to clock drift between devices and the complexity of direct device pairing, which is not suitable for precise synchronization of scratching behavior measurements.
Innovation Solution
Utilizing cardiac activity measured by optical heart rate sensors on both devices to synchronize recordings, aligning clocks based on interbeat intervals and applying clock-time correction to ensure synchronization within a threshold duration, allowing separate pairing and communication through a hub device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If clock-time correction is implemented by equipping both wearable devices with communication means to synchronize at the start or periodically, then synchronization precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent introduces a hub device as an intermediary that performs clock-time correction for multiple wearable devices. Instead of each wearable device having direct communication capability to synchronize with others, the hub device receives data from all wearables and applies correction algorithms, eliminating the need for complex peer-to-peer communication protocols between wearables while maintaining synchronization precision.
Solution Approach 2:
The patent enables wearables to self-synchronize by having them independently transmit their data to the hub device, which then automatically applies clock correction based on reference clocks. The wearables themselves don't need active synchronization capabilities - they simply need to send their measurements, and the hub handles the complex timing alignment autonomously.
2Measurement precision
If clock-time correction is implemented through direct pairing between wearable devices, then synchronization precision is improved, but software complexity increases
Solution Approach 1:
The hub device serves as a central intermediary that manages all synchronization logic. Instead of implementing complex pairing protocols between each pair of wearable devices, the system uses the hub as a single point of coordination that applies reference clock corrections to all devices' data uniformly, dramatically simplifying the software architecture.
Solution Approach 2:
The hub device performs multiple functions including data collection from all wearables, clock-time correction using reference clocks, and data processing. This universal approach eliminates the need for each wearable to have specialized synchronization software, as the hub's multi-functional correction system handles all timing alignment needs.
3Device complexity
If a posteriori synchronization based on body movements is used, then device complexity is reduced, but measurement precision deteriorates for scratching behavior monitoring
Solution Approach 1:
The hub device acts as an intermediary that introduces reference clocks as a stable timing reference. Instead of relying on imperfect body-movement-based synchronization, the hub uses these reference clocks to provide accurate time stamps for all wearable data, enabling precise measurement of scratching behavior while keeping the wearable devices themselves simple.
Solution Approach 2:
The patent replaces the mechanical/body-movement-based synchronization approach with an electronic reference clock system. Rather than using physical body movements (which are inherently variable and unreliable for synchronization) to align timestamps, the system uses stable electronic reference clocks provided by the hub device to achieve precise temporal alignment.
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
Ensures accurate synchronization of accelerometer-based metrics by correcting clock drift, enabling precise monitoring of scratching behavior and providing effective feedback to healthcare providers.
Implementation Method 1
which can be measured with a reflective photoplethysmography sensor
Data Source
Figure 1
Figure 2(A)~2(D)
Figure 3
AI summary
A method for synchronizing recordings of two wearable devices (12,14) worn by a user (16) in a specific use case is designed to measure a characteristic behaviour of the user over a period of time. The method comprises acquiring first recordings via a first wearable device (12) operable via a first clock, and acquiring concurrent second recordings via a second wearable device (14) operable via a second clock, wherein each clock has a clock drift and offset. The first and second wearable devices are synced with a hub executable app (18) executed on a hub device (20). A clock-time correction (62) is implemented via the hub executable app before processing (64) the respective recordings for the specific use case. The clock-time correction ensures that respective recordings have been corrected in time so that a difference between clocks, or clock drift, of the two wearable devices is no more than a threshold duration of a shortest event specific to the characteristic behaviour being measured.