ANTENNAS AND PROPAGATION FOR BODY AREA NETWORKS AT 60 GHZ by XIANYUE WU A thesis submitted to the University of Birmingham for the degree of Doctor of Philosophy School of Electronic, Electrical & Computer Engineering College of Engineering and Physical Sciences University of Birmingham September 2013 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract The advent of wireless body area networks (WBANs) and their use in a wide range of applications from consumer electronics to military purposes, dictates the need to investi- gate to the behaviour of antennas and wave propagation on the body in depth. Although this area has been extensively studied in the past decade, some issues are still not satis- factorily solved for communication systems for WBANs at ISM bands and UWB such as compact and high efficiency antenna design, privacy and security, interference mitigation and achieving high data rates. This thesis proposed an alternative wireless solution for body area networks by adopting 60 GHz radio. On-body channels at 60 GHz have been characterised using monopole and horn antennas. Horn antennas achieve significantly improved path gain in the stable channels but are susceptible to shadowing in the mo- bile channels due to body movements. However, interference mitigation and covertness for 60 GHz WBANs at the physical layer are improved due to high attenuation of 60 GHz signals. Significant increase of carrier-to-interference ratio is observed for 60 GHz WBANs compared to 2.45 GHz. A model of estimating the maximum detection distance at a threshold probability for detecting a WBAN wearing soldier in a battlefield is pro- posed. Fixed-beam directional antennas and reconfigurable antennas are designed for 60 GHz WBANs and channel measurements using these antennas are conducted. Results show beam-reconfigurability of the antenna improves the link performance compared to fixed-beam antennas at 60 GHz. To My Parents Acknowledgements My first debt of gratitude must go to my supervisors Professor Peter S. Hall and Dr. Costas Constantinou. They patiently provided the vision, encouragement and advice necessary for me to proceed through the doctoral program and complete my thesis. I want to thank them for their unflagging encouragement and serving as role models to me as a junior member of academia. I had a great opportunity to visit the University of Virginia as a part of my PhD. The whole experience was unique and I would like to acknowledge Professor John Lach for his great advice. I would like to thank examiners of my thesis, Professor William Scanlon and Dr. Alexan- dros Feresidis, for their time and feedback on my work. I would also like to express my deep gratitude to my colleague, Dr. Yuriy I. Nechayev, who has been very supportive and generous in sharing his knowledge. I am very greatful to Mr. Alan Yates for providing all the technical support. Special thanks to my other brilliant colleagues and very nice friends, Dr. Zhengpeng Wang, Dr. Lida Akhoonzadeh- Asl, Dr. Mohammad Hmaid, Dr. Zhenhua Hu, Mr. Xiao Li, Mr. Philip Asare from the University of Virginia and Dr. Nacer Chahat from the University of Renne 1 for their kind help and friendship. I also want to thank Engineering and Physical Sciences Research Council for providing me the opportunity and partial funding to pursue my PhD degree. Last but not least, I would like to thank my beloved parents, for their endless support, love and understanding. Acronyms AFD Average Fade Duration BAN Body Area Network BSN Body Sensor Network CDF Cumulative Distribution Function CIR Carrier to Interference Ratio DOA Direction Of Arrival DRA Dielectric Resonator Antenna DSSS Direct Sequence Spread Spectrum EBG Electromagnetic Band Gap ECG Electrocardiography EEG Electroencephalography EMG Electromyography FCC Federal Communications Commission FDA Food and Drug Administration FDTD Finite Difference Time Domain FHSS Frequency-Hopping Spread Spectrum ISM Industrial Scientific and Medical LCR Level Crossing Rate LOS Line Of Sight LTCC Low Temperature Co-fired Ceramic MBAN Medical Body Area Network MEMS Microelectromechanical System MICS Medical Implant Communication Service NBI Narrowband Interference NLOS Non Line Of Sight OMT Orthomode Transducer PCB Printed Circuit Board pdf Probability Density Function PDP Power Delay Profile PIFA Planar Inverted-F Antenna ROC Receiver Operating Characteristic RSSI Received Signal Strength Indicator RMS Root Mean Square SAR Radiation Absorption Rate SINR Signal to Interference plus Noise Ratio SIW Substrate Integrated Waveguide SNR Signal to Noise Ratio UWB Ultra-wide Band VNA Vector Network Analyser WBAN Wireless Body Area Network WLAN Wireless Local Area Network Contents 1 Introduction 1 1.1 Introduction to Body Area Networks . . . . . . . . . . . . . . . . . . . . . 1 1.2 Technological Issues on Body Area Networks . . . . . . . . . . . . . . . . . 4 1.3 Why Study Antennas and Propagation? . . . . . . . . . . . . . . . . . . . 6 1.4 Summary of the Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.5 Layout of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 Overview of Antennas and Propagation for WBANs 10 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Basic Concepts and Theories . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.1 Cumulative Distribution Function . . . . . . . . . . . . . . . . . . . 11 2.2.2 Level Crossing Rate and Average Fade Duration . . . . . . . . . . . 11 2.2.3 Two-port Network and S-Parameters . . . . . . . . . . . . . . . . . 13 2.2.4 Path Loss and Path Gain . . . . . . . . . . . . . . . . . . . . . . . 14 2.3 Radio Channel Characterisation for WBANs . . . . . . . . . . . . . . . . . 15 2.3.1 Channel measurements and empirical models . . . . . . . . . . . . . 16 2.3.2 Simulations and human phantoms . . . . . . . . . . . . . . . . . . . 21 2.3.3 Characterisation of Dynamic Body Effects . . . . . . . . . . . . . . 23 2.4 Wearable Antenna Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.4.1 On-body conventional antennas . . . . . . . . . . . . . . . . . . . . 25 2.4.2 Textile antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.5 Interference and Covertness for WBANs . . . . . . . . . . . . . . . . . . . 29 2.5.1 Narrowband interference . . . . . . . . . . . . . . . . . . . . . . . . 30 2.5.2 UWB interference . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3 Introduction to 60 GHz Wireless Body Area Networks 35 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3.2 Benefits and challenges for 60 GHz WBANs . . . . . . . . . . . . . . . . . 37 3.3 60 GHz Wireless Communications . . . . . . . . . . . . . . . . . . . . . . . 38 3.4 Review of 60 GHz Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4 Measurement Methods 43 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43