Wireless time synchronization of a collaborative brain-computer-interface using bluetooth low energy

A wireless EEG-system with high channel density (up to 256) was developed for bio-potential data recording. In order to use this system for a collaborative brain-computer-interface (BCI) multiple EEG sub-systems with a common visually and auditory evoked potential (VEP/AEP) stimulator, a video camera and a PC, all connected to a WLAN, are required. Since each of the components has its own software clock typically based on a quartz crystal, a difference in skew and offset between all system components is induced after a few seconds from their cold start; this is due to the quartz instability of ±50 ppm. To evaluate evoked potentials of different test subjects synchronous in time in a group experiment scenario, it is necessary to implement a common time reference among the entire system. To achieve time synchronization without modifying the existing hardware/software a novel synchronization add-on, and a synchronization center based on Bluetooth were implemented and experimentally evaluated.