Modelling and characterisation of antennas and propagation for body-centric wireless communication

PhDBody-Centric Wireless Communication (BCWC) is a central point in the development of fourth generation mobile communications. The continuous miniaturisation of sensors, in addition to the advancement in wearable electronics, embedded software, digital signal processing and biomedical technologies, have led to a new concept of usercentric networks, where devices can be carried in the user’s pockets, attached to the user’s body or even implanted. Body-centric wireless networks take their place within the personal area networks, body area networks and body sensor networks which are all emerging technologies that have a broad range of applications such as healthcare and personal entertainment. The major difference between BCWC and conventional wireless systems is the radio channel over which the communication takes place. The human body is a hostile environment from radio propagation perspective and it is therefore important to understand and characterise the effect of the human body on the antenna elements, the radio channel parameters and hence the system performance. This is presented and highlighted in the thesis through a combination of experimental and electromagnetic numerical investigations, with a particular emphasis to the numerical analysis based on the finite-difference time-domain technique. The presented research work encapsulates the characteristics of the narrowband (2.4 GHz) and ultra wide-band (3-10 GHz) on-body radio channels with respect to different digital phantoms, body postures, and antenna types hence highlighting the effect of subject-specific modelling, static and dynamic environments and antenna performance on the overall body-centric network. The investigations covered extend further to include in-body communications where the radio channel for telemetry with medical implants is also analysed by considering the effect of different digital phantoms on the radio channel characteristics. The study supports the significance of developing powerful and reliable numerical modelling to be used in conjunction with measurement campaigns for a comprehensive understanding of the radio channel in body-centric wireless communication. It also emphasises the importance of considering subject-specific electromagnetic modelling to provide a reliable prediction of the network performance

On Application of Wireless Sensor Networks for Healthcare Monitoring

With the recent advances in embedded systems and very low power ,wireless tech­ nologies, there has been a great interest in the development and application of a new class of distributed Wireless body area network for health monitoring. The first part of the thesis presents a remote patient monitoring system within the scope of Body Area Network standardization. In this regime, wireless sensor networks are used to continuously acquire the patient’s Electrocardiogram signs and transmit data to the base station via IEEE.802.15. The personal Server (PS) which is responsible to provide real-time displaying, storing, and analyzing the patient’s vital signs is developed in MATLAB. It also transfers ECG streams in real-time to a remote client such as a physician or medical center through internet. The PS has the potential to be integrated with home or hospital computer systems. A prototype of this system has been developed and implemented. Tlie developed system takes advantage of two important features for healthcare monitoring: (i) ECG data acqui­ sition using wearable sensors and (ii) real-time data remote through internet. The fact that our system is interacting with sensor network nodes using MATLAB makes it distinct from other previous works. The second part is devoted to the study of indoor body-area channel model for 2.4 GHz narrowband communications. To un­ derstand the narrowband radio propagation near the body, several measurements are carried out in two separate environments for different on body locations. On the basis of these measurements, we have characterized the fading statistics on body links and we have provided a physical interpretation of our results

On Research Challenges in Hybrid Medium Access Control Protocols for IEEE 802.15.6 WBANs

IEEE 802.15.6 is a Wireless Body Area Network (WBAN) standard proposed to facilitate the exponentially growing interest in the field of health monitoring. This standard is flexible and outlines multiple basic Medium Access Control (MAC) protocols that are contention based and collision free to meet the WBAN Quality of Service (QoS) challenges. Typically, current research trends in WBAN MAC focus on designing a hybrid MAC that is a combination of basic MAC protocols. In this paper, we provide a first detailed survey of existing hybrid MAC protocols based on IEEE 802.15.6 which would be useful for the related research community. Firstly, the paper lists the design challenges of a WBAN MAC. Secondly, it highlights the significance of hybrid MAC protocols in meeting the design challenges while comparing them to standard MAC protocols. Thirdly, a critical and thorough comparison of existing hybrid MAC protocols is presented in terms of network QoS and WBAN specific parameters. Lastly, we identify key open research areas that are often neglected in hybrid MAC design and further propose some possible directions for future research

Fault tolerance in WBAN applications

One of the most promising applications of IoT is Wireless Body Area Net-works (WBANs) in medical applications. They allow physiological signals monitoring of patients without the presence of nearby medical personnel. Furthermore, WBANs enable feedback action to be taken either periodically or event-based following the Networked Control Systems (NCSs) techniques. This thesis first presents the architecture of a fault tolerant WBAN. Sensors data are sent over two redundant paths to be processed, analyzed and monitored. The two main communication protocols utilized in this system are Low power Wi-Fi (IEEE 802.11n) and Long Term Evolution (LTE). Riverbed Modeler is used to study the system’s behavior. Simulation results are collected with 95% confidence analysis on 33 runs on different initial seeds. It is proven that the system is fully operational. It is then shown that the system can withstand interference and system’s performance is quantified. Results indicate that the system succeeds in meeting all required control criteria in the presence of two different interference models. The second contribution of this thesis is the design of an FPGA-based smart band for health monitoring applications in WBANs. This FPGA-based smart band has a softcore processor and its allocated SRAM block as well as auxiliary modules. A novel scheme for full initial configuration and Dynamic Partial Reconfiguration through the WLAN network is integrated into this design. Fault tolerance techniques are used to mitigate transient faults such as Single Event Upsets (SEUs) and Multiple Event Upsets (MEUs). The system is studied in a normal environment as well as in a harsh environment. System availability is then obtained using Markov Models and a case study is presented

Antenna de-­embedding for on­-body communications with wearables and implants

The particular challenge for modeling wearable and implantable wireless systems for on-body communications lies in the near-field coupling of the antenna and the dissipative tissue. Hence, so far, the antennas could not be considered separately from the propagation channel in the system description. Therefore, methods for the systematic antenna design of on-body applications are developed, whereas the antennas are characterized de-embedded. First, a method for characterizing on-body antennas is developed based on physical modeling of the propagation along the tissue. Furthermore, on-body antenna parameters are derived, representing an adapted form of the standard free-space antenna parameters. Secondly, a method for modeling on-body links based on spherical wave functions (SWF) is developed. It enables obtaining separate models of the antennas and the channel at a higher level of abstraction. Since the developed on-body antenna parameters are defined closely to the standard free-space definitions, an intuitive characterization of on-body antennas is possible. Furthermore, an antenna test range is developed for assessing the defined on-body antenna parameters for physical prototypes. As shown by the examples evaluated, the on-body antenna parameters and the determined transmission equation, analogous to the Friis equation in free-space, can also be used to model the entire wireless system. However, the difficulty lies in determining the directional channel model, which is costly and not universally possible for any application. The developed method based on SWF complements the characterization methods, as channels of any complexity can be modeled since the method could be implemented numerically. Beyond the characterization of on-body antennas and channels, the design of optimized antennas for these applications presents a substantial challenge. Based on the derived on-body transmission equation, antenna optimization can be done directly by maximizing the on-body antenna gain in the direction of the main propagation path. For more complex channels, antenna optimization based on SWF modeling is also developed. With this, optimal characteristics of the antenna can be calculated based on many different possible channel models. To also obtain a possibility for validation with measurements here, both developed methods are linked with each other so that a determination of the on-body antenna parameters is also possible based on the optimal SWF coefficients. With several application examples, it has been validated that the developed methods enable efficient de-embedded modeling and educated design of wearable and implanted antennas for on-body communications.Die besondere Herausforderung bei der Modellierung von am Körper getragenen und implantierbaren drahtlosen Systemen liegt in der Nahfeldkopplung der Antenne und des dissipativen Gewebes. Daher konnten bisher die Antennen nicht getrennt vom Ausbreitungskanal in der Systembeschreibung berücksichtigt werden. Aus diesem Grund werden Methoden für die systematische Antennenentwicklung von On-Body-Anwendungen entwickelt, wobei die Antennen separat (de-embedded) charakterisiert werden können. Zunächst wird eine Methode zur Charakterisierung von On-Body-Antennen entwickelt, die auf der physikalischen Modellierung der Ausbreitung entlang des Gewebes basiert. Darüber hinaus wurden On-Body-Antennenparameter abgeleitet, die eine angepasste Form der Standardantennenparameter für den freien Raum darstellen. Desweiteren wird eine Methode zur Modellierung von On-Body-Verbindungen auf Grundlage von sphärischen Wellenfunktionen entwickelt. Diese ermöglicht es, getrennte Modelle der Antennen und des Kanals auf einer höheren Abstraktionsebene zu erhalten. Da die entwickelten On-Body-Antennenparameter in enger Anlehnung an die Standarddefinitionen für den freien Raum definiert sind, ist eine intuitive Charakterisierung von On-Body-Antennen möglich. Weiterhin wird ein Antennenmesssystem entwickelt, um die definierten Antennenparameter für physische Prototypen auswerten zu können. Wie die untersuchten Beispiele zeigen, können die On-Body-Antennenparameter und die ermittelte Übertragungsgleichung, analog zur Friis-Gleichung im Freiraum, auch zur Modellierung des gesamten Funksystems verwendet werden. Die Schwierigkeit liegt hier jedoch in der Bestimmung des Kanalmodells, die aufwändig und nicht für jede Anwendung universell möglich ist. Die entwickelte Methode auf Basis sphärischer Wellenfunktionen (SWF) ergänzt die Charakterisierungsmethoden, da aufgrund der numerischen Implementierung hiermit Kanäle beliebiger Komplexität modelliert werden können. Neben der Charakterisierung von On-Body-Antennen und -Kanälen stellt der Entwurf von optimierten Antennen für diese Anwendungen eine große Herausforderung dar. Mithilfe der abgeleiteten Übertragungsgleichung für On-Body Antennen kann die Antennenoptimierung direkt basierend auf den On-Body Antennenparametern erfolgen, indem der Gewinn der On-Body Antenne in Richtung des Hauptausbreitungspfads maximiert wird. Für komplexere Kanäle wird auch eine Antennenoptimierung auf der Grundlage der SWF-Modellierung entwickelt. Auf diese Weise können die optimalen Eigenschaften der Antenne auf Grundlage vieler verschiedener möglicher Kanalmodelle berechnet werden. Um auch hier eine Möglichkeit zur messtechnischen Validierung zu erhalten, werden beide entwickelten Methoden miteinander verknüpft, sodass eine Bestimmung der On-Body Antennenparameter auch auf Basis der SWF-Koeffizienten möglich ist. Anhand mehrerer Anwendungsbeispiele konnte validiert werden, dass die entwickelten Methoden eine effiziente Modellierung sowie ein fundiertes Design von tragbaren und implantierten Antennen für die On-Body-Kommunikation ermöglichen

Human exposure to electromagnetic fields from WLANs and WBANs in the 2.4 GHz band

226 p.En los últimos años, el masivo crecimiento de las comunicaciones inalámbricas ha incrementado la preocupación acerca de la exposición humana a los campos electromagnéticos debido a los posibles efectos sobre la salud. Esta tesis surge de la necesidad de proporcionar información acerca de este tipo de exposición desde un punto de vista técnico. Por una parte, se han estudiado los niveles de exposición causados por señales WiFi, para lo cual ha sido necesario establecer un procedimiento de medida adecuado para tomar muestras de estas emisiones. Además, se han llevado a cabo campañas de medida para evaluar la exposición a señales WiFi y su variabilidad en el interior de un entorno público. Por otra parte, se ha analizado la potencia absorbida por el cuerpo humano a causa de los novedosos dispositivos wearables. Se han implementado dos antenas de este tipo, apropiadas para dispositivos wearables, se ha analizado detalladamente la exposición debida a estos aparatos y finalmente se han comparado los niveles de exposición producidos por estas antenas y por las señales WiFi