Signal (Stream) synchronization with White noise sources, in biomedical applications

Abstract

When multiple acquisition systems are used to simultaneously acquire signals, synchronization issues may arise potentially causing errors in the determination of acquisition starting points and continuous clock offsets and shifts on each device. This paper introduces a processing method to efficiently synchronize these signals in the presence of white noise sources without the requirement of clock sharing or any other digital line exchange. The use of a signal source, such as white noise with a very wide frequency band, is of great interest for synchronization purposes, due to its aperiodic nature. This high bandwidth signal is simultaneously acquired by all the acquisition channels, on distinct systems, and, synchronized afterwards using cross-correlation methods. Two different correlation methods were tested; a global method, used when clock system frequencies are exactly known, and a local method, used when independent clocks evidence shifts over time that cumulatively account for long term acquisition errors in the synchronization process. In a computational simulation with known clock frequencies the results show a synchronization error of ≈1/10 of the time resolution, for both methods. For unknown clock frequencies, the global method achieved an error of 24/10 the time resolution, indicating a much poorer performance. In the experimental setup , only the local method was tested. The best result shows a synchronization error of 4/10 of the time resolution. All the signal conditioning and acquisition parameters were chosen taking into account potential biomedical applications.

Timing errors and temporal uncertainty in clinical databases—A narrative review

“…This method of synchronization requires artifacts or features from multiple time points throughout the signals to ensure that clock drift is properly accounted for ( 85 ). Another interesting approach to signal synchronization involves simultaneous introduction of white noise to both signals while they are being recorded ( 217 ). White noise has rich frequency characteristics that facilitate signal alignment yet is also random enough that it doesn't interfere with the information content of the signals.…”

IBSync: Intra-body synchronization and implicit contextualization of wearable devices using artificial ECG landmarks

“…These achieved typical synchronization errors ranging from 250 ms down to 46 ms. Beyond that, Vaz et al (2015) proposed the correlation and alignment of physiological signal channels by means of the inherently present white noise. The achieved sub-ms accuracy is, however, bought dearly through high sampling rates of 2 and 20 kHz.…”

IBSync: Intra-body Synchronization of Wearable Devices Using Artificial ECG Landmarks

“…In recent years, more advanced methods using motion patterns [8,9,30,50] or cough events [1] have been proposed. Even the white noise inherently present in physiological signals was proposed for the correlation and alignment of signal channels [49]. The "naturally synchronized" heartbeat has also been used in a time division multiple access (TDMA) protocol for medium-access control (MAC) [29].…”