Synchronization of Wearable Sensor Data for Vital Sign Monitoring

Wearables are increasingly popular and are being accepted in healthcare applications, such as monitoring activity and heart rate. Like other wireless sensors, time synchronization is an important issue to ensure the credibility of data. While studies in this area are not uncommon, most methods try to synchronize the clock on individual devices and require access to the hardware and modification to the firmware. We consider a case for consumer wearables, where there is zero access to both firmware and hardware of the devices, except listening to the streaming data passively, and all synchronization can only be done on the receiving end. We present a two-part approach to synchronize streaming data received from wearable sensors. First, the fixed time offset due to device processing time is corrected by a one-time calibration. Second, the random time offset due to wireless communication is corrected by finetuning the sampling rate. Instead of adjusting the time on separate devices, the method attempts to align data from different devices to the accuracy of one sample time. The synchronization method also considers situations of data loss, congested Bluetooth channels, and multiple receiving hubs. With further interpolation on the received data, a synchronization accuracy of 1 ms is achieved. Unlike existing methods that rely on embedded timestamps, synchronized start events, or firmware modifications, our technique operates entirely on the receiver side, achieving single sample accuracy even under packet loss and clock drift.