Wireless Positioning and Tracking for Internet of Things in GPS-denied Environments

Wireless positioning and tracking have long been a critical technology for various applications such as indoor/outdoor navigation, surveillance, tracking of assets and employees, and guided tours, among others. Proliferation of Internet of Things (IoT) devices, the evolution of smart cities, and vulnerabilities of traditional localization technologies to cyber-attacks such as jamming and spoofing of GPS necessitate development of novel radio frequency (RF) localization and tracking technologies that are accurate, energy-efficient, robust, scalable, non-invasive and secure. The main challenges that are considered in this research work are obtaining fundamental limits of localization accuracy using received signal strength (RSS) information with directional antennas, and use of burst and intermittent measurements for localization. In this dissertation, we consider various RSS-based techniques that rely on existing wireless infrastructures to obtain location information of corresponding IoT devices. In the first approach, we present a detailed study on localization accuracy of UHF RF IDentification (RFID) systems considering realistic radiation pattern of directional antennas. Radiation patterns of antennas and antenna arrays may significantly affect RSS in wireless networks. The sensitivity of tag antennas and receiver antennas play a crucial role. In this research, we obtain the fundamental limits of localization accuracy considering radiation patterns and sensitivity of the antennas by deriving Cramer-Rao Lower Bounds (CRLBs) using estimation theory techniques. In the second approach, we consider a millimeter Wave (mmWave) system with linear antenna array using beamforming radiation patterns to localize user equipment in an indoor environment. In the third approach, we introduce a tracking and occupancy monitoring system that uses ambient, bursty, and intermittent WiFi probe requests radiated from mobile devices. Burst and intermittent signals are prominent characteristics of IoT devices; using these features, we propose a tracking technique that uses interacting multiple models (IMM) with Kalman filtering. Finally, we tackle the problem of indoor UAV navigation to a wireless source using its Rayleigh fading RSS measurements. We propose a UAV navigation technique based on Q-learning that is a model-free reinforcement learning technique to tackle the variation in the RSS caused by Rayleigh fading

Wireless Localization Systems: Statistical Modeling and Algorithm Design

Wireless localization systems are essential for emerging applications that rely on context-awareness, especially in civil, logistic, and security sectors. Accurate localization in indoor environments is still a challenge and triggers a fervent research activity worldwide. The performance of such systems relies on the quality of range measurements gathered by processing wireless signals within the sensors composing the localization system. Such range estimates serve as observations for the target position inference. The quality of range estimates depends on the network intrinsic properties and signal processing techniques. Therefore, the system design and analysis call for the statistical modeling of range information and the algorithm design for ranging, localization and tracking. The main objectives of this thesis are: (i) the derivation of statistical models and (ii) the design of algorithms for different wire- less localization systems, with particular regard to passive and semi-passive systems (i.e., active radar systems, passive radar systems, and radio frequency identification systems). Statistical models for the range information are derived, low-complexity algorithms with soft-decision and hard-decision are proposed, and several wideband localization systems have been analyzed. The research activity has been conducted also within the framework of different projects in collaboration with companies and other universities, and within a one-year-long research period at Massachusetts Institute of Technology, Cambridge, MA, USA. The analysis of system performance, the derived models, and the proposed algorithms are validated considering different case studies in realistic scenarios and also using the results obtained under the aforementioned projects

Sistemas eficientes de transmissão de energia sem-fios e identificação por radiofrequência

Doutoramento em Engenharia EletrotécnicaIn the IoT context, where billions of connected objects are expected to be ubiquitously deployed worldwide, the frequent battery maintenance of ubiquitous wireless nodes is undesirable or even impossible. In these scenarios, passive-backscatter radios will certainly play a crucial role due to their low cost, low complexity and battery-free operation. However, as passive-backscatter devices are chiefly limited by the WPT link, its efficiency optimization has been a major research concern over the years, gaining even more emphasis in the IoT context. Wireless power transfer has traditionally been carried out using CW signals, and the efficiency improvement has commonly been achieved through circuit design optimization. This thesis explores a fundamentally different approach, in which the optimization is focused on the powering waveforms, rather than the circuits. It is demonstrated through theoretical analysis, simulations and measurements that, given their greater ability to overcome the built-in voltage of rectifying devices, high PAPR multi-sine (MS) signals are capable of more efficiently exciting energy harvesting circuits when compared to CWs. By using optimal MS signals to excite rectifying devices, remarkable RF-DC conversion efficiency gains of up to 15 dB with respect to CW signals were obtained. In order to show the effectiveness of this approach to improve the communication range of passive-backscatter systems, a MS front-end was integrated in a commercial RFID reader and a significant range extension of 25% was observed. Furthermore, a software-defined radio RFID reader, compliant with ISO18000-6C standard and with MS capability, was constructed from scratch. By interrogating passive RFID transponders with MS waveforms, a transponder sensitivity improvement higher than 3 dB was obtained for optimal MS signals. Since the amplification and transmission of high PAPR signals is critical, this work also proposes efficient MS transmitting architectures based on space power combining techniques. This thesis also addresses other not less important issues, namely self-jamming in passive RFID readers, which is the second limiting factor of passive-backscatter systems. A suitable self-jamming suppression scheme was first used for CW signals and then extended to MS signals, yielding a CW isolation up to 50 dB and a MS isolation up 60 dB. Finally, a battery-less remote control system was developed and integrated in a commercial TV device with the purpose of demonstrating a practical application of wireless power transfer and passive-backscatter concepts. This allowed battery-free control of four basic functionalities of the TV (CH+,CH-,VOL+,VOL-).No contexto da internet das coisas (IoT), onde são esperados bilhões de objetos conectados espalhados pelo planeta de forma ubíqua, torna-se impraticável uma frequente manutenção e troca de baterias dos dispositivos sem fios ubíquos. Nestes cenários, os sistemas radio backscatter passivos terão um papel preponderante dado o seu baixo custo, baixa complexidade e não necessidade de baterias nos nós móveis. Uma vez que a transmissão de energia sem fios é o principal aspeto limitativo nestes sistemas, a sua otimização tem sido um tema central de investigação, ganhando ainda mais ênfase no contexto IoT. Tradicionalmente, a transferência de energia sem-fios é feita através de sinais CW e a maximização da eficiência é conseguida através da otimização dos circuitos recetores. Neste trabalho explora-se uma abordagem fundamentalmente diferente, em que a otimização foca-se nas formas de onda em vez dos circuitos. Demonstra-se, teoricamente e através de simulações e medidas que, devido à sua maior capacidade em superar a barreira de potencial intrínseca dos dispositivos retificadores, os sinais multi-seno (MS) de elevado PAPR são capazes de excitar os circuitos de colheita de energia de forma mais eficiente quando comparados com o sinal CW tradicional. Usando sinais MS ótimos em circuitos retificadores, foram verificadas experimentalmente melhorias de eficiência de conversão RF-DC notáveis de até 15 dB relativamente ao sinal CW. A fim de mostrar a eficácia desta abordagem na melhoria da distância de comunicação de sistemas backscatter passivos, integrou-se um front-end MS num leitor RFID comercial e observou-se um aumento significativo de 25% na distância de leitura. Além disso, desenvolveu-se de raiz um leitor RFID baseado em software rádio, compatível com o protocolo ISO18000-6C e capaz de gerar sinais MS, com os quais interrogou-se transponders passivos, obtendo-se ganhos de sensibilidade dos transponders maiores que 3 dB. Uma vez que a amplificação de sinais de elevado PAPR é uma operação crítica, propôs-se também novas arquiteturas eficientes de transmissão baseadas na combinação de sinais em espaço livre. Esta tese aborda também outros aspetos não menos importantes, como o self-jamming em leitores RFID passivos, tido como o segundo fator limitativo neste tipo de sistemas. Estudou-se técnicas de cancelamento de self-jamming CW e estendeu-se o conceito a sinais MS, tendo-se obtido isolamentos entre o transmissor e o recetor de até 50 dB no primeiro caso e de até 60 dB no segundo. Finalmente, com o objetivo de demonstrar uma aplicação prática dos conceitos de transmissão de energia sem fios e comunicação backscatter, desenvolveu-se um sistema de controlo remoto sem pilhas, cujo protótipo foi integrado num televisor comercial a fim de controlar quatro funcionalidades básicas (CH+,CH-,VOL+,VOL-)

Digital Beamforming Techniques for Passive UHF RFID Tag Localization

Radio-frequency identification (RFID) technology is on the way to substitute traditional bar codes in many fields of application. Especially the availability of passive ultra-high frequency (UHF) RFID transponders (or tags) in the frequency band between 860 MHz and 960 MHz has fostered the global application in supply chain management. However, the full potential of these systems will only be exploited if the identification of objects is complemented by accurate and robust localization. Passive UHF RFID tags are cost-effective, very small, extremely lightweight, maintenancefree, rugged and can be produced as adhesive labels that can be attached to almost any object. Worldwide standards and frequency regulations have been established and a wide infrastructure of identification systems is operated today. However, the passive nature of the technology requires a simple communication protocol which results in two major limitations with respect to its use for localization purposes: the small signal bandwidth and the small allocated frequency bandwidth. In the presence of multipath reflections, these limitations reduce the achievable localization accuracy and reliability. Thus, new methods have to be found to realize passive UHF RFID localization systems which provide sufficient performance in typical multipath situations. In this thesis, an enhanced transmission channel model for passive UHF RFID localization systems has been proposed which allows an accurate estimation of the channel behaviour to multipath. It has been used to design a novel simulation environment and to identify three solutions to minimize multipath interference: a) by varying the channel interface parameters, b) by applying diversity techniques, c) by installation of UHF absorbers. Based on the enhanced channel model, a new method for tag readability prediction with high reliability has been introduced. Furthermore, a novel way to rate the magnitude of multipath interference has been proposed. A digital receiver beamforming localization method has been presented which uses the Root MUSIC algorithm for angulation of a target tag and multipath reducing techniques for an optimum localization performance. A new multiangulation algorithm has been proposed to enable the application of diversity techniques. A novel transmitter beamforming localization approach has been presented which exploits the precisely defined response threshold of passive tags in order to achieve high robustness against multipath. The basic technique has been improved significantly with respect to angular accuracy and processing times. Novel experimental testbeds for receiver and transmitter beamforming have been designed, built and used for verification of the localization performance in real-world measurements. All the improvements achieved contribute to an enhancement of the accuracy and especially the robustness of passive UHF RFID localization systems in multipath environments which is the main focus of this researc

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Real-time localization using received signal strength

Locating and tracking assets in an indoor environment is a fundamental requirement for several applications which include for instance network enabled manufacturing. However, translating time of flight-based GPS technique for indoor solutions has proven very costly and inaccurate primarily due to the need for high resolution clocks and the non-availability of reliable line of sight condition between the transmitter and receiver. In this dissertation, localization and tracking of wireless devices using radio signal strength (RSS) measurements in an indoor environment is undertaken. This dissertation is presented in the form of five papers. The first two papers deal with localization and placement of receivers using a range-based method where the Friis transmission equation is used to relate the variation of the power with radial distance separation between the transmitter and receiver. The third paper introduces the cross correlation based localization methodology. Additionally, this paper also presents localization of passive RFID tags operating at 13.56MHz frequency or less by measuring the cross-correlation in multipath noise from the backscattered signals. The fourth paper extends the cross-correlation based localization algorithm to wireless devices operating at 2.4GHz by exploiting shadow fading cross-correlation. The final paper explores the placement of receivers in the target environment to ensure certain level of localization accuracy under cross-correlation based method. The effectiveness of our localization methodology is demonstrated experimentally by using IEEE 802.15.4 radios operating in fading noise rich environment such as an indoor mall and in a laboratory facility of Missouri University of Science and Technology. Analytical performance guarantees are also included for these methods in the dissertation --Abstract, page iv

Sensors and Systems for Indoor Positioning

This reprint is a reprint of the articles that appeared in Sensors' (MDPI) Special Issue on “Sensors and Systems for Indoor Positioning". The published original contributions focused on systems and technologies to enable indoor applications