Time Synchronization in Multimodal Wireless Cyber-Physical Systems: A Wearable Biopotential Acquisition and Collaborative Brain-Computer Interface Paradigm

Die Forschung zu Brain-Computer Interface (BCI) hat in den letzten drei Jahren riesige Fortschritte gemacht, nicht nur im Bereich der menschlich gesteuerten Roboter, der Steuerung von Prothesen, des Interpretierens von Wörtern, der Kommunikation in einer Virtual Reality Umgebung oder der Computerspiele, sondern auch in der kognitiven Neurologie. Patienten, die unter enormen motorischen Dysfunktionen leiden (letztes Stadium Amyotrophe Lateralsklerose) könnten solch ein BCI System als alternatives Medium zur Kommunikation durch die eigene Gehirnaktivität nutzen. Neuste Studien zeigen, dass die Verwendung dieses BCI Systems in einem Gruppenexperiment helfen kann die menschliche Entscheidungstreffung deutlich zu verbessern. Dies ist ein neues Feld des BCI, nämlich das Collaborative BCI. Einerseits erfordert die Durchführung solch eines Gruppenexperiments drahtlose Hochleistungs-EEG Systeme, basierend auf BCI, welches kostengünstig und tragbar sein sollte und Langzeit-Monitoring hochwertiger EEG Daten sicherstellt. Andererseits ist es erforderlich, eine Zeitsynchronisierung zwischen den einzelnen BCI Systemen einzusetzen, damit diese für ein Gruppenexperiment zum Einsatz kommen können. Diese Herausforderungen setzten die Grundlage dieser Doktorarbeit. In dieser Arbeit wurde ein neuartiges, nicht invasives, modulares, biopotentiales Messsystem entwickelt: Dieses kann Breitband (0.5 Hz–150 Hz) Biopotentiale ableiten, bestehend aus Elektromyographie (EMG), Elektrokardiografie (EKG), Elektroencephalografie (EEG), wurde insgesamt bezeichnet als ExG bzw. das Messsystem als ExG-System benannt. Die Modularität des ExG-Systems erlaubt 8 bis hin zu 256 Kanäle zu konfigurieren, je nach Anforderung, ob in einen textilen Schlauch eingekapselt zur Erfassung von EMG Signalen, in eine textilen Weste zur Erfassung von ECG Signalen oder in eine textilen Kappe zur Erfassung von EEG Signalen. Der Einbau des ExG-Systems in eine Kappe wurde ebenfalls im Rahmen der Arbeit entwickelt. Der letzte Schritt des ExG-Systems zeigt niedriges Eingangsrauschen von 7 µVvon-Spitze-zu-Spitze und benötigt 41 mW/Kanal der Datenaufnahme im aktiven Zustand. Ein WiFi-Modul wurde für eine drahtlose Datenübertragung an einen ferngesteuerten PC in das ExG-System eingebaut. Um mit dem entwickelte System BCI Anwendungen zu ermöglichen, wurde ein akustisch und visuell evozierter Potenzialstimulator (SSVEP/AEP Stimulator) entwickelt. In eben diesem wurde ein Rasperry Pi als Zentralrechner benutzt und ein Bash basiertes Player-Skript iii einprogrammiert, das Mediadaten (Video, Audio, Ton) aus der Angabe einer Lookup Tabelle (LUT) in ihr Linux Betriebssystem spielt. Im Rahmen der Arbeit wurde eine Zeitsynchronisierung an einigen dieser ExG-Systeme mit Hilfe von einer eingebetteten Hardware/Softwarelösung durchgeführt. Die Hardwareteile bestehen aus einigen Leiterplatten, nämlich Sync Modulen mit einem Quarzoszillator, einem Mikrocontroller und einem Funkmodul (Hierbei Bluetooth 4.0). Eines von diesen ist das Sync-Addon, das mit jedem Messsystem (z.B. ExG-System) das zu synchronisieren ist, angeschlossen wird. Das andere bezeichnet man als Sync-Center, das an die Datenverarbeitungsrechner angehängt wird. Das Softwareteil übernimmt den Zeitsynchronisierungsmechanismus mit Hilfe eines funkbasierten Protokolls. Im Rahmen der Arbeit wurde ein neues energieeffizientes pairwise broadcast Zeitsynchronisationsprotokoll (PBS), welches nur theoretisch vorgestellt wurde, experimentell verifiziert. Außerdem wurde es mit anderen bestehenden Zeitsynchronisationsprotokollen auf dem aktuellen Stand der Technik evaluiert, basierend auf den Ergebnissen der gleichen Hardwareebene. In der letzten Iteration der Sync-Module wurde ein durchschnittlicher Synchronisationsfehler von 2 ms, den Konfidenzintervall von 95% berücksichtigend, erlangt. Da für Collaborative BCI, P300, ein Ereignis bezogenes Potenzial mit dem Auslöseimpuls, der 300−500 ms nach dem Vorgang eintritt, eingestellt wurde, ist die erreichte Synchronisationsgenauigkeit genügend, um solch ein Experiment durchzuführen.Brain-computer interface (BCI) has experienced the last three decades tremendous technological advances not only in the field of human controller robotics, or in controlling prosthesis, or in spelling words, or in interacting with a virtual reality environment, or in gaming but also in cognitive neuroscience. Patients suffering from severe motoric dysfunction (e.g. late stage of Amyotrophic Lateral Sclerosis) may utilise such a BCI system as an alternative medium of communication by mental activity. Recently studies have shown that usage of such BCI in a group experiment can help to improve human decision making. This is a new field of BCI, namely collaborative BCI. On one hand, performing such group experiments require wireless, high density EEG system based BCI which should be low-cost, wearable and provide long time monitoring of good quality EEG data. On the other hand time synchronization is required to be established among a group of BCI systems if they are employed for such a group experiments. These drawbacks set the foundation of this thesis work. In this work a novel non-invasive modular biopotential measurement system which can acquire wideband (0.15 Hz–200 Hz) biopotential signals consisting Electromyography (EMG), Electrocardiography (ECG), Electroencephalography (EEG) together called ExG, following ExG-system was designed. The modularity of the ExG-system allows it to be configured from 8 up to 256 channels according to the requirement if it’s to be encapsulated in a textile sleeve for recording of EMG signals, or in a textile vest for recording of ECG signals, or in a textile cap for recording of EEG signals. The assembly of the ExG-system in cap was also developed during the scope of the work. The final iteration of the ExG-system exhibits low input noise of 7 µVpeak-to-peak and require 41 mW/channel of data recording in active state. A WiFi module was embedded into the ExG-system for wireless data transmission to a remote PC. To enable the developed system for BCI applications a steady-state visually/auditory evoked potential stimulator (SSVEP/AEP stimulator) incorporating a Raspberry Pi as a main computer and a bash based player script which plays media data (video, pictures, sound) as defined in a lookup table in the Linux operating system of it. Within the scope of the work time synchronization among a group of such ExG-systems was further realized with the help of an embedded hardware/software solution. The hardware part consists of two different PCB sync modules that are incorporated with a crystal oscillator a microcontroller, a radio module (in this case Bluetooth 4.0). One of them is called the v sync-addon which is to be attached to each of the measurement systems (e.g. ExG-system) that are to be synchronized and the sync-center which is to be attached to the remote PC. On the software part, a wireless time synchronization protocol exchanging timing information among the sync-center and sync-addons must establish tight time synchronization between the ExG-system. Within the framework of this work, a novel time synchronization protocol energy efficient pairwise broadcast synchronization protocol (PBS) that was only theoretically proposed before but not evaluated on real hardware was experimentally evaluated with the developed sync modules. Moreover a benchmarking with other state-of-the-art existing time synchronization protocols based on the results from same hardware platform were drawn. In the final iteration of sync modules an average synchronization error of 2 ms was achieved considering the 95% of confidence interval. Since for collaborative BCI, P300, an event related potential was triggered with the stimuli that occur 300−500 ms after the event, the achieved synchronization accuracy is sufficient to conduct such experiments

Energy Efficiency in Communications and Networks

The topic of "Energy Efficiency in Communications and Networks" attracts growing attention due to economical and environmental reasons. The amount of power consumed by information and communication technologies (ICT) is rapidly increasing, as well as the energy bill of service providers. According to a number of studies, ICT alone is responsible for a percentage which varies from 2% to 10% of the world power consumption. Thus, driving rising cost and sustainability concerns about the energy footprint of the IT infrastructure. Energy-efficiency is an aspect that until recently was only considered for battery driven devices. Today we see energy-efficiency becoming a pervasive issue that will need to be considered in all technology areas from device technology to systems management. This book is seeking to provide a compilation of novel research contributions on hardware design, architectures, protocols and algorithms that will improve the energy efficiency of communication devices and networks and lead to a more energy proportional technology infrastructure

Dependability of Wireless Sensor Networks

As wireless sensor networks (WSNs) are becoming ever more prevalent, the runtime characteristics of these networks are becoming an increasing issue. Commonly, external sources of interference make WSNs behave in a different manner to that expected from within simplistic simulations, resulting in the need to use additional systems which monitor the state of the network. Despite dependability of WSNs being an increasingly important issue, there are still only a limited number of works within this specific field, with the majority of works focusing on ensuring that specific devices are operational, not the application as a whole. This work instead aims to look at the dependability of WSNs from an application-centric view, taking into account the possible ways in which the application may fail and using the application's requirements to focus on assuring dependability

Recent Trends in Communication Networks

In recent years there has been many developments in communication technology. This has greatly enhanced the computing power of small handheld resource-constrained mobile devices. Different generations of communication technology have evolved. This had led to new research for communication of large volumes of data in different transmission media and the design of different communication protocols. Another direction of research concerns the secure and error-free communication between the sender and receiver despite the risk of the presence of an eavesdropper. For the communication requirement of a huge amount of multimedia streaming data, a lot of research has been carried out in the design of proper overlay networks. The book addresses new research techniques that have evolved to handle these challenges

An automated framework for power-efficient detection in embedded sensor systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 191-200).The availability of miniature low-cost sensors has allowed for the capture of rich, multimodal data streams in compact embedded sensor nodes. These devices have the capacity to radically improve the quality and amount of data available in such diverse applications as detecting degenerative diseases, monitoring remote regions, and tracking the state of smart assets as they traverse the supply chain. However, current implementations of these applications suffer from short lifespans due to high sensor energy use and limited battery size. By concentrating our design efforts on the sensors themselves, it is possible to construct embedded systems that achieve their goal(s) while drawing significantly less power. This will increase their lifespan, allowing many more applications to make the transition from laboratory to marketplace and thereby benefit a much wider population. This dissertation presents an automated framework for power-efficient detection in embedded sensor systems. The core of this framework is a decision tree classifier that dynamically orders the activation and adjusts the sampling rate of the sensors, such that only the data necessary to determine the system state is collected at any given time.(cont.) This classifier can be tuned to trade-off accuracy and power in a structured fashion. Use of a sensor set which measures the phenomena of interest in multiple modalities and at various rates further improves the power savings by increasing the information available to the classification process. An application based on a wearable gait monitor provides quantitative support for this framework. It is shown that the decision tree classifiers designed achieve roughly identical detection accuracies to those obtained using support vector machines while drawing three to nine times less power. A simulation of the real-time operation of the classifiers demonstrates that our multi-tiered classifier determines states as accurately as a single-trigger (binary) wakeup system while drawing half as much power, with only a negligible increase in latency.by Ari Yosef Benbasat.Ph.D

Low power digital baseband core for wireless Micro-Neural-Interface using CMOS sub/near-threshold circuit

This thesis presents the work on designing and implementing a low power digital baseband core with custom-tailored protocol for wirelessly powered Micro-Neural-Interface (MNI) System-on-Chip (SoC) to be implanted within the skull to record cortical neural activities. The core, on the tag end of distributed sensors, is designed to control the operation of individual MNI and communicate and control MNI devices implanted across the brain using received downlink commands from external base station and store/dump targeted neural data uplink in an energy efficient manner. The application specific protocol defines three modes (Time Stamp Mode, Streaming Mode and Snippet Mode) to extract neural signals with on-chip signal conditioning and discrimination. In Time Stamp Mode, Streaming Mode and Snippet Mode, the core executes basic on-chip spike discrimination and compression, real-time monitoring and segment capturing of neural signals so single spike timing as well as inter-spike timing can be retrieved with high temporal and spatial resolution. To implement the core control logic using sub/near-threshold logic, a novel digital design methodology is proposed which considers INWE (Inverse-Narrow-Width-Effect), RSCE (Reverse-Short-Channel-Effect) and variation comprehensively to size the transistor width and length accordingly to achieve close-to-optimum digital circuits. Ultra-low-power cell library containing 67 cells including physical cells and decoupling capacitor cells using the optimum fingers is designed, laid-out, characterized, and abstracted. A robust on-chip sense-amp-less SRAM memory (8X32 size) for storing neural data is implemented using 8T topology and LVT fingers. The design is validated with silicon tapeout and measurement shows the digital baseband core works at 400mV and 1.28 MHz system clock with an average power consumption of 2.2 μW, resulting in highest reported communication power efficiency of 290Kbps/μW to date

Intelligent Sensor Networks

In the last decade, wireless or wired sensor networks have attracted much attention. However, most designs target general sensor network issues including protocol stack (routing, MAC, etc.) and security issues. This book focuses on the close integration of sensing, networking, and smart signal processing via machine learning. Based on their world-class research, the authors present the fundamentals of intelligent sensor networks. They cover sensing and sampling, distributed signal processing, and intelligent signal learning. In addition, they present cutting-edge research results from leading experts

A Novel Long-Range Passive UHF RFID System over Twisted-pair Cable

Radio Frequency Identification (RFID) is one of the most representative, rapidly growing, and highly extendable technologies, which uses electromagnetic waves in accordance with specific communications standards and regulations to identify, track, or even localise desired objects. However, due to its high cost, limited read range, and uncertain reliability, its adoption still lags, especially in large-scale organisations. Even though an RFID distributed antenna system (DAS) can greatly improve the detection range and read rate of a single reader when system uses different combinations of antenna states with frequency and phase hopping, the lossy and heavy coaxial cables between reader and antennas still limits the system coverage and design flexibility for wide-area passive UHF RFID applications. In order to develop a cost-efficient and flexibly-installed passive RFID DAS, a novel large-range passive UHF RFID system over twisted-pair cable is proposed in this dissertation. This new system consists of one baseband central controller and one antenna subsystem, connected by a commonly used twisted-pair cable. It is shown that transmitting/receiving low frequency baseband signals over a twisted-pair cable can significantly reduce cable attenuation and extend the communication distance. A simulation is conducted to demonstrate that frequency and phase hopping can also be remotely controlled to fit this system structure by slightly varying the frequency or phase of the input reference signal of the frequency synthesis system. The features of twisted-pair cable in terms of its low cost, light weight, and bend radius greatly improve the design and installation flexibility of an RFID system. The implemented system is designed based on the ISO 18000-6C and EPC Class 1 Generation 2 standards, and can operate according to FCC (902-928 MHz) and ETSI (865-868MHz) regulations. The results of the measurement show the reader can achieve a sensitivity of - 94.5 dBm over 30 m Cat5e cable, and its sensitivity can still remain at around -94.2 dBm over 150 m Cat5e cable. The experimental results of tag detection show that the passive tags can be successfully detected over a 6 m wireless range following a 300 m of twisted-pair cable between the central controller and antenna. This detection range cannot be achieved by existing commercial RFID systems. Since the transmission and reception in a RFID system are simultaneous, finite isolation of the circulator/directional coupler and environmentally dependent reflection ratio of the antenna lead to serious leakage problems. Leakage can directly cause sensitivity degradation due to saturation of the RF components. A fast leakage suppression block is developed in efforts to solve this problem. Measurements show that this new canceller can deliver an average suppression of 36.9 dB, and this excellent performance remains when the system uses frequency hopping. With help of an improved scanning algorithm, this canceller can find its optimal status within 38 ms, and this settling time is short enough for most commercial RFID readers. By reducing the number of voltage samples taken, the convergence time can be further improved. To fully investigate this new passive UHF RFID system value, a comparison study between the new system and a commercial system is conducted. This new automatic passive UHF RFID system is confirmed to deliver high performance long-range passive tag detection. Particular advantages are shown in the fast tag read rate and capability of uplink SNR improvement. This novel system is also superior to conventional RFID systems in terms of link distance, link cost, and installation flexibility