COMPLEX PULSE FORMING TEACHNIQUE USING AM DETECTOR TYPE CIRCUITRY AND THE APPLICATION OF CDMA TO RFID FOR THE SIMULTANEOUS READING OF MULTIPLE TAGS

A novel complex ultra wideband RF pulse forming technique has been implemented in this research, using the coefficients derived from discrete Fourier transform of a virtual pulse train. Incorporated in this technique is a multiple frequency communication systems designed such that transmitter receiver proximity and the fading effect of the individual frequencies make part of a corresponding modulation technique. A code division multiple access (CDMA) application to RFID to greatly reduce read time, while at the same time eliminating inter tag interference, has been investigated with the analysis of a typical cart aisle scenario. With the current rate of growth of inventory world wide there is a tremendous need for more efficient method of data gathering, data storage, and data retrieval. In this dissertation, the application of the CDMA RFID technology has been analyzed to demonstrate the potentials of integrating the RFID technology to the EPC global numbering system

Anti-collision techniques for RFID systems.

Chiang Kong Wa.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (leaves 74-79).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 2 --- Technology Overview --- p.4Chapter 2.1 --- Components of RFID Systems --- p.5Chapter 2.1.1 --- Tag --- p.6Chapter 2.1.2 --- Reader --- p.9Chapter 2.1.3 --- Software systems --- p.10Chapter 2.1.4 --- Communication infrastructure --- p.11Chapter 2.2 --- Frequency Regulations and Standards --- p.11Chapter 2.2.1 --- RFID frequency bands --- p.11Chapter 2.2.2 --- Standards --- p.12Chapter 2.3 --- Advantages and Limitations of RFID Technology --- p.14Chapter 2.4 --- Applications --- p.17Chapter 3 --- Background of Research --- p.20Chapter 3.1 --- Anti-collision methods for RFID systems --- p.22Chapter 3.1.1 --- Stochastic Anti-collision Protocols --- p.25Chapter 3.1.2 --- Deterministic Anti-collision Protocols --- p.27Chapter 4 --- Even-Odd Binary Tree Protocol --- p.30Chapter 4.1 --- Protocol Description --- p.31Chapter 4.2 --- Time Complexity Analysis --- p.34Chapter 4.3 --- Performance Evaluation --- p.37Chapter 4.4 --- Summary --- p.41Chapter 5 --- Prefix-Randomized Query-Tree Protocol --- p.44Chapter 5.1 --- Tag Identification - Known Tag Set Size --- p.45Chapter 5.1.1 --- Protocol Description --- p.45Chapter 5.1.2 --- Time Complexity Analysis --- p.47Chapter 5.1.3 --- Optimal Initial Prefix Length --- p.50Chapter 5.1.4 --- Optimal Number of Level-1 Nodes --- p.52Chapter 5.2 --- Tag Identification - Unknown Tag Set Size --- p.53Chapter 5.2.1 --- Initial Prefix Length Adaptation Algorithm --- p.54Chapter 5.2.2 --- Computing r*Δ(l) --- p.55Chapter 5.2.3 --- Optimal Choice of Step Size Δ --- p.56Chapter 5.3 --- Performance Evaluation --- p.59Chapter 5.4 --- Summary --- p.64Chapter 6 --- Conclusion and Future Work --- p.68Chapter 6.1 --- Conclusion --- p.68Chapter 6.2 --- Future Work --- p.70Bibliography --- p.7

Contributions to the development of active RFID systems at the 433 MHz band

Donat el potencial de la tecnologia RFID activa, aquesta tesi contribueix al seu desenvolupament centrant-se en les capes més baixes de la pila de protocols, és a dir, la capa física i la capa d'enllaç de dades. Aquestes capes determinen l'abast de la comunicació entre l'interrogador i les etiquetes, el nombre d'etiquetes que un interrogador pot llegir per segon i el consum d'energia que utilitzen les etiquetes en el procés, que en són els paràmetres de rendiment clau. A la capa física la tesi avalua els aspectes de propagació de la banda 433 MHz en diferents entorns i els compara amb la banda 2.4 GHz. Els resultats demostren que, per a la mateixa potència de transmissió, els sistemes RFID actius que funcionen a la banda 433 MHz aconsegueixen un millor abast de comunicació gràcies a unes millors característiques de propagació. A la capa d'enllaç de dades la tesi proposa LPDQ (Low-Power Distributed Queuing), un nou protocol d'accés al medi, i el compara amb FSA (Frame Slotted ALOHA). LPDQ combina LPL (Low-Power Listening) per a la sincronització de xarxa i DQ (Distributed Queuing) per a la transmissió de dades. En comparació amb el cas òptim de FSA, LPDQ aconsegueix un rendiment proper al màxim teòric (99.5%) independentment del nombre d'etiquetes i redueix el consum d'energia de les etiquetes en més d'un 10%.Dado el potencial de la tecnología RFID activa, esta tesis contribuye a su desarrollo centrándose en las capas más bajas de la pila de protocolos, es decir, la capa física y la capa de enlace de datos. Estas capas determinan el alcance de la comunicación entre el interrogador y las etiquetas, el número de etiquetas que un interrogador puede leer por segundo y el consumo de energía que utilizan las etiquetas en el proceso, que son los parámetros de rendimiento clave. En la capa física la tesis evalúa los aspectos de propagación de la banda 433 MHz en diferentes entornos y los compara con la banda 2.4 GHz. Los resultados demuestran que, para la misma potencia de transmisión, los sistemas RFID activos que funcionan en la banda 433 MHz consiguen un mejor alcance de comunicación gracias a unas mejores características de propagación. En la capa de enlace de datos la tesis propone LPDQ (Low-Power Distributed Queuing), un nuevo protocolo de acceso al medio, y lo compara con FSA (Frame Slotted ALOHA). LPDQ combina LPL (Low-Power Listening) para la sincronización de red y DQ (Distributed Queuing) para la transmisión de datos. En comparación con el caso óptimo de FSA, LPDQ consigue un rendimiento cercano al máximo teórico (99.5%) independientemente del número de etiquetas y reduce el consumo de energía de las etiquetas en más de un 10%.Given the potential of active RFID technology, this thesis contributes to its development by focusing on the lowest layers of the stack, that is, the physical and data-link layers. These layers determine the tag communication range, packet throughput and energy consumption, which are key performance parameters. At the physical layer, the thesis studies propagation aspects of the 433 MHz band in different environments and compares it to the 2.4 GHz band, which is also used in active RFID systems. The results demonstrate that active RFID systems operating at the 433 MHz band can achieve a better communication range at the same transmit power due to better propagation characteristics. At the data-link layer, the thesis proposes LPDQ (Low-Power Distributed Queuing), a new MAC (media access control) protocol, and compares it to FSA (Frame Slotted ALOHA). LPDQ combines LPL (Low-Power Listening) for network synchronization and DQ (Distributed Queuing) for data transmission. Compared to the optimal FSA case, LPDQ can achieve a performance close to the theoretical maximum (99.5%), regardless of the number of tags, and reduces tag energy consumption by more than 10%

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

Reliable Communication in Wireless Networks

Wireless communication systems are increasingly being used in industries and infrastructures since they offer significant advantages such as cost effectiveness and scalability with respect to wired communication system. However, the broadcast feature and the unreliable links in the wireless communication system may cause more communication collisions and redundant transmissions. Consequently, guaranteeing reliable and efficient transmission in wireless communication systems has become a big challenging issue. In particular, analysis and evaluation of reliable transmission protocols in wireless sensor networks (WSNs) and radio frequency identification system (RFID) are strongly required. This thesis proposes to model, analyze and evaluate self-configuration algorithms in wireless communication systems. The objective is to propose innovative solutions for communication protocols in WSNs and RFID systems, aiming at optimizing the performance of the algorithms in terms of throughput, reliability and power consumption. The first activity focuses on communication protocols in WSNs, which have been investigated, evaluated and optimized, in order to ensure fast and reliable data transmission between sensor nodes. The second research topic addresses the interference problem in RFID systems. The target is to evaluate and develop precise models for accurately describing the interference among readers. Based on these models, new solutions for reducing collision in RFID systems have been investigated

Realistic chipless RFID: protocol, encoding and system latency

Chiplose Identifikation über Funkfrequenzen, RFID (engl., Radio Frequency IDentification) ist eine vielversprechende Technology, der man die Fähigkeit zuschreibt, in naher Zukunft den optischen Barcode zu ersetzen. Letztgenannter hat Einschränkungen durch i) RFID Tags sind bei nicht vorhandener Sichtverbindung (engl. Non-Line-Of-Sight, NLOS) auch nicht lesbar; ii) das Scannen der Barcodes benötigt in den meisten Fällen manuelles Eingreifen; iii) es ist unmöglich mehrere Barcodes gleichzeitig auszulesen; iv) und als Folge davon entsprechende Verzögerungen beim Auslesen größerer Mengen von Barcodes, da alle einzeln gescannt werden müssen. Die Beiträge der vorliegenden Dissertation konzentrieren sich auf drei Schwerpunkte von frequenzcodierten (engl. frequency coded, FC) chiplosen RFID Systemen. Der erste Schwerpunkt ist die gleichzeitige Identifikation von mehreren RFID Tags und kümmert sich um den Fall, dass sich mehrere RFID Tags in der Lesezone des RFID Lesegerätes befinden. Der zweite Aspekt betrifft die Verzögerung des Systems, die Zeit, das Lesegerät zum Identifizieren der RFID Tags benötigt. Und drittens die Coding Kapazität des Systems, sie ist verantwortlich für die zu erreichende Bittiefe des RFID Systems. Ein real umsetzbares RFID System erfordert Lösungen in allen drei Aspekten. Da chiplose RFID Tags keine integrierten Schaltungen (ICs) und somit auch keine Speicherbausteine besitzen, ist die Anzahl der auf dem RFID Tag speicherbaren Bits begrenzt. Und als Folge davon sind die Standards und Protokolle, die für die herkömmlichen chipbehafteten RFID Systeme entwickelt worden, nicht auf chiplose RFID Systeme übertragbar. Das wesentliche Ziel des ersten Beitrages ist die Einführung eines neuen Multi-Tag Antikollisionsprotokolls, das auf der Modulation der Notchposition (engl. Notch Position Modulation, NPM) und Tabellen (engl. Look-Up-Table, LUT) zur Bestimmung der Netzwerk- und MAC- Layer des chiplosen RFID Systems basiert. Die erste Generation der vorgeschlagenen Protokolls (Gen-1) baut auf einer Zweiteilung des zur Verfügung stehenden Spektrums auf. Im unteren Frequenzbereich, als Präambel Bandbreite bezeichnet, wird jedem RFID Tag seine individuelle Frequenzverschiebung übermittelt und im zweiten Bereich, der sogenannten Frame Bandbreite, ist die Identifikationsnummer (ID) des RFID Tags hinterlegt. Mit dieser Anordnung lässt sich jegliche Interferenz zwischen den verschiedenen RFID Tags unterbinden, da sich die Antworten der RFID Tags nicht gegenseitig überlagern. Die zweite Generation dieses Protokolls bringt eine Verbesserung sowohl bei der Coding Kapazität als auch bei der Nutzung des zur Verfügung stehenden Frequenzspektrums. Dies wird dadurch erreicht, dass die ID des RFID in einer Tabelle im Lesegerät gespeichert wird. Die individuelle Frequenzverschiebung dient dabei als Adresse für die gespeicherten IDs. Dieser Schritt vereinfacht die Komplexität der Struktur des RFID Tags signifikant, während gleichzeitig die Erkennungswahrscheinlichkeit erhöht wird. Des Weiteren werden die Key Performance Indikatoren untersucht um die Leistungsfähigkeit der Protokolle zu beweisen. Beide Protokollversionen werden modelliert und in einer Umgebung mit 10 chiplosen RFID Tags simuliert, um die Randbedingungen für die Entwicklung der RFID Tags und des RFID Lesegerätes zu ermitteln. Außerdem wird eine neuartige Testumgebung für ein MultiTag Ultra Breitband (engl. ultra wideband UWB) RFID System unter realen Testbedingungen basierend auf einem Software Defined Radio (SDR) Ansatz entwickelt. In dieser Testumgebung werden sowohl die gesendeten Signal als auch Detektierungstechniken, Leerraum Kalibrierung zur Reduzierung der Streustrahlung und die Identifikationsprotokolle untersucht. Als zweiter Schwerpunkt dieser Arbeit werden neue Techniken zur Reduzierung der Systemlaufzeit (engl. System Latency) eingeführt. Das Ziel dabei ist, die Zeit, die das RFID Lesegerät zum Erkennen aller in Lesereichweite befindlichen chiplosen FC RFID Tags braucht, zu verkürzen. Der Großteil der Systemlaufzeit wird durch das gewählte Frequenzscanverfahren, durch die Anzahl der Mittelungen zur Eliminierung der umgebenden Streustrahlung und durch die Dauer eines Frequenzsprungs bestimmt. In dieser werden dazu ein adaptives Frequenzsprungverfahren (engl. adaptive frequency hopping, AFH) sowie ein Verfahren Mittels adaptiver gleitender Fensterung (engl. adaptive sliding window, ASW) eingeführt. Das ASW Verfahren ist dabei im Hinblick auf die Identifizierung der RFID Tags nach dem Gen-1 Protokoll entwickelt, da es ein gleitendes Fenster zur Detektierung der Notches mit einer variablen Breite zum Auslesen der ID erfordert. Im Gegensatz dazu wird das Auffinden der im Gen-2 Protokoll verwendeten Notchpattern durch das AFH Verfahren verbessert. Dies wird über variable Frequenzsprünge, die auf die jeweiligen Notchpattern optimiert werden, erreicht. Beide Verfahren haben sich als effektiv sowohl im Hinblick auf die Systemlaufzeit als auch auf die Genauigkeit erwiesen. Das ASW und das AFH Verfahren wurden dazu in der oben erwähnten Testumgebung implementiert und mit dem klassischen Frequenzsprungverfahren, feste feingraduierte Frequenzschritte, verglichen. Die Experimente haben gezeigt, dass das vorgeschlagene AFH Verfahren in Kombination mit ASW zu einer beachtlichen Reduzierung der Systemlaufzeit von 58% führen. Das Ziel des dritten Schwerpunkts dieser Arbeit ist die Einführung einer neuartigen Technik zur Erhöhung der Informationsdichte (engl. Coding capacity) in einem chiplosen FC RFID Systems. Die hierfür vorgeschlagene Modulation der Notchbreite (engl. notch width modulation, NWM) ermöglicht die Kodierung von 4 Bits (16 Zuständen) pro Resonator in dem die Notchbreite und die dazugehörige Frequenzlage ausgenutzt werden. Für jeden Notch werden 150MHz Bandbreite reserviert, innerhalb derer das Codebit durch eine bestimmte Bandbreiten an unterschiedlichen Frequenzen bestimmt wird Cj ( fk,Bl). Das bedeutet, bei einer Arbeitsfrequenz im Bereich von 2–5 GHz können so 80 Bits realisiert werden. Des Weiteren wurde eine smarte Singulärwertzerlegung (engl. smart singular value decomposition, SSVD) Technik entwickelt, um die Notchbreite zu ermitteln und eine geringe Fehlerwahrscheinlichkeit zu garantieren. Die Nutzung von Blockcodes zur Behebung von Fehlern wurde untersucht, um den größtmöglichen Nutzen aus der so gewonnene Bittiefe zu erzielen. Als Folge konnte eine große Bittiefe mit einer hohen Lesegenauigkeit bei vereinfachtem Aufbau des Lesegeräts erzielt werden. Außerdem wurde eine neuartige RFID Tag Struktur entworfen, die bei einer Größe von 4× 5 cm2 eine Codedichte von 4 Bits/cm2 erreicht. Verschiedene RFID Tag Konfigurationen wurden erstellt und das neu eingeführte Codierungsverfahren mit Hilfe von elektromagnetischen (EM) Simulation und der bereits erwähnten Testplattform überprüft. Die erzielten Ergebnisse ermöglichen ein widerstandsfähiges RFID System in einer realen Umgebung. Alle vorgeschlagenen Beiträge sind durch analytische Modelle, Simulationen und Messungen auf mögliche Probleme und die Grenzen einer Realisierung unter realistischen Bedingungen geprüft worden.Chipless Radio Frequency IDentification (RFID) is a promising technology predicted to replace the optical barcode in the near future. This is due to several problematic issues i) the barcode cannot read Non-Line-Of-Sight (NLOS) tags; ii) each barcode needs human assistance to be read; iii) it is impossible to identify multiple tags at the same time; and iv) the considerable time delay in case of massive queues because different types of objects need to be serially scanned. The contributions included in this dissertation concentrate on three main aspects of the Frequency Coded (FC) chipless RFID system. The first one is the multi-tag identification, which deals with the existence of multiple tags in the reader’s interrogation region. The second aspect is the system latency that describes the time the reader needs to identify the tags. Finally, there is the coding capacity that is responsible for designing a chipless tag with larger information bits. The aim of these aspects is to realize a chipless RFID system. Since the chipless tags are memoryless as they do not include Integrated Circuits (ICs), the number of bits to be stored in the chipless tag is limited. Consequently, the current RFID standards and protocols designed for the chipped RFID systems are not applicable to the chipless systems. The main objective of the first contribution is to introduce novel multi-tag anti-collision protocols based on Notch Position Modulation (NPM) and Look-Up-Table (LUT) schemes determining the network and MAC layers of the chipless RFID systems. The first generation of the proposed protocol (Gen-1) relies on dividing the spectrum into two parts; the first one is the preamble bandwidth that includes a unique frequency shift for each tag. The second part is the frame bandwidth which represents the tag ID. The tag ID is obtained based on the predefined frequency positions, making use of the unique frequency shift. Consequently, the interference is avoided as there will not be any overlap between the tags’ responses. The second generation of the protocol (Gen-2) introduces an improvement in the spectrum utilization and coding capacity. This is realized by transferring the tag-ID to be stored in a table in the main memory of the reader (look-up-table). The unique shift of each tag represents the address of the tag’s ID. Therefore, the complexity of the tag structure will be significantly reduced with an enhanced probability of detection. Furthermore, the key performance indicators for the chipless RFID system are explored to validate the protocol’s performance. Both protocols are modeled and simulated to identify 10-chipless tags in order to set the regulations of the tag and reader design. Moreover, a novel real-world testbed for a multi-tag Ultra Wideband (UWB) chipless RFID system based on Software Defined Radio (SDR) is introduced. In this testbed, all the signaling schemes related to the transmitted signal, the detection techniques, the empty room calibration for the clutter removal process, and the identification protocols are applied. The aim of the second aspect is to introduce novel techniques that reduce the time required by the reader to identify the FC chipless RFID tags existent in the reader’s interrogation region. This time delay is called system latency. The main parameters that significantly affect the overall system latency are the frequency scanning methodology, the number of spectrum scanning iterations for the clutter removal process, and the hop duration. Therefore, the Adaptive Frequency Hopping (AFH) and the Adaptive Sliding Window (ASW) methodologies are proposed to meet the requirements of the FC chipless RFID tags. Regarding the ASW technique, it is suitable to identify the tags using the Gen-1 protocol which utilizes a sliding window (for detecting the notch) with an adaptive size to extract the tag’s-ID. The second adaptive methodology, AFH, can identify the tags with the Gen-2 protocol by using a variable frequency step that fits the corresponding notch patterns. These techniques are proven to be efficient for the chipless RFID systems with regard to latency and accuracy. Likewise, the designed AFH and ASW technique’s performance is compared to the classical Fixed Frequency Hopping (FFH) methodology with a fine frequency step to validate the accuracy of the proposed techniques. A real-world SDR based testbed is designed and the proposed adaptive algorithms as well as the classical FFH methodology are implemented. The experiments show that the proposed AFH combined with the ASW algorithms significantly reduce the system latency by 58%. The goal of the third aspect is to introduce a novel technique that increases the coding capacity of the FC chipless RFID system. The proposed Notch Width Modulation (NWM) scheme encodes 4 bits (16-combinations) per single resonator exploiting the notch bandwidth and its corresponding frequency position. Furthermore, each notch can reserve a window with a bandwidth of 150 MHz and inside this window the notch can obtain a certain bandwidth with a specific resonant frequency constructing the coding pairs Cj ( fk,Bl). Hence, 80-bits could be achieved at the operating frequency 2–5 GHz, preserving the operating frequency bandwidth. Also, a Smart Singular Value Decomposition (SSVD) technique is designed to estimate the notch bandwidth and to ensure a low probability of error. In addition, the utilization of a linear block code as an error correcting code is explored to make the best use of the obtained coding gain. Consequently, a high encoding efficiency and an accurate detection can be achieved in addition to a simplified reader design. Moreover, a novel 4× 5 cm2 tag structure is designed to meet the requirements of the NWM coding technique achieving a coding density of 4 bits/cm2. Different tag configurations are manufactured and validated by measurements using the SDR platform. The introduced coding methodology is conclusively validated using Electromagnetic (EM) simulations and real-world testbed measurements. The considered achievements for the proposed aspects offer a robust chipless RFID system that can be considered in real scenarios. Furthermore, all the proposed contributions are validated using analytical modeling, simulation and measurements in order to list their difficulties and limitations

Towards zero-power wireless machine-to-machine networks

This thesis aims at contributing to overcome two of the main challenges for the deployment of M2M networks in data collection scenarios for the Internet of Things: the management of massive numbers of end-devices that attempt to get access to the channel; and the need to extend the network lifetime. In order to solve these challenges, two complementary strategies are considered. Firstly, the thesis focuses on the design, analysis and performance evaluation of MAC protocols that can handle abrupt transitions in the traffic load and minimize the energy consumption devoted to communications. And secondly, the use of energy harvesting (EH) is considered in order to provide the network with unlimited lifetime. To this end, the second part of the thesis focuses on the design and analysis of EH-aware MAC protocols. While the Frame Slotted-ALOHA (FSA) protocol has been traditionally adopted in star topology networks for data collection, results show that FSA-based protocols lack of scalability and present synchronization problems as the network density increases. Indeed, the frame length of FSA must be adjusted to the number of contenders, which may be complex to attain in dense networks with large and dynamic number of end-devices. In order to overcome these issues, a tree splitting-based random access protocol, referred to as Low Power Contention Tree-based Access (LP-CTA), is proposed in the first part of this thesis. In LP-CTA, the frame length can be very short and fixed, which facilitates synchronization and provides better network scalability than FSA. While LP-CTA uses data slots for contention, it is possible to use short access requests in minislots, where collisions are resolved using tree splitting, and avoid the contention in data. Since these minislots can be much shorter than the duration of a data packet, the performance can be improved. The Low Power Distributed Queuing (LP-DQ) protocol proposed in this thesis is based on this idea. LP-DQ combines tree splitting with the logic of two distributed queues that manage the contention resolution and the collision-free data transmission. Results show that LP-DQ outperforms LP-CTA and FSA in terms of delay and energy efficiency, and it relaxes the need to know the size of the network and adapts smoothly to any change in the number of end-devices. The approach of LP-DQ is convenient when the messages transmitted by each end-device fit in one single slot, however, if the end-devices generate long messages that have to be fragmented, it is better to add a reservation mechanism in order to boost the performance. In this sense, the LPR-DQ protocol is proposed as an extension of LP-DQ where the concept of reservation is integrated to allow the end-devices reserve as many collision-free slots as needed. The second part of the thesis is devoted to the integration of the MAC layer with the use of energy harvesting. The variability and fluctuations of the harvested energy is considered for the design of EH-aware MAC protocols and three performance metrics are proposed: the probability of delivery, the data delivery ratio and the time efficiency. Previous works on data collection networks with EH focus on DFSA. In this thesis, the EH-CTA protocol is proposed as an adaptation of LP-CTA that takes the energy harvesting process into account. Results show that EH-CTA outperforms DFSA if the energy threshold for an end-device to become active is properly configured. In addition, while DFSA needs to adapt the frame length dynamically, EH-CTA uses a fixed frame length, thus facilitating scalability and synchronization. Finally, the EH-RDFSA and EH-DQ protocols are proposed for scenarios where data must be fragmented. EH-RDFSA is a combination of RFSA and DFSA, and EH-DQ is an extension of LPR-DQ.Esta tesis contribuye a resolver dos de los retos para el despliegue de redes M2M en escenarios de recolección de datos para el Internet de las Cosas: la gestión del acceso al canal de un número masivo de dispositivos; y la necesidad de extender la vida de la red. Para resolverlos se consideran dos estrategias complementarias. En primer lugar, se centra en el diseño, el análisis y la evaluación de protocolos MAC que pueden manejar transiciones abruptas de tráfico y reducen el consumo de energía. Y en segundo lugar, se considera el uso de mecanismos de captura de energía (Energy Harvesters, EH) para ofrecer un tiempo de vida ilimitado de la red. Con este fin, la segunda parte de la tesis se centra en el diseño y el análisis de protocolos MAC de tipo "EH-aware". Mientras que Frame Slotted-ALOHA (FSA) ha sido tradicionalmente adoptado en aplicaciones de recolección de datos, los resultados muestran que FSA presenta problemas de escalabilidad y sincronización cuando aumenta la densidad de la red. De hecho, la longitud de trama de FSA se debe ajustar según sea el número de dispositivos, lo cual puede ser difícil de estimar en redes con un número elevado y dinámico de dispositivos. Para superar estos problemas, en esta tesis se propone un protocolo de acceso aleatorio basado en "tree-splitting" denominado Low Power Contention Tree-based Access (LP-CTA). En LP-CTA, la longitud de trama puede ser corta y constante, lo cual facilita la sincronización y proporciona mejor escalabilidad. Mientras que LP-CTA utiliza paquetes de datos para la contienda, es posible utilizar solicitudes de acceso en mini-slots, donde las colisiones se resuelven utilizando "tree-splitting", y evitar la contención en los datos. Dado que estos mini-slots pueden ser mucho más cortos que la duración de un slot de datos, el rendimiento de LP-CTA puede ser mejorado. El protocolo Low Power Distributed Queuing (LP-DQ) propuesto en esta tesis se basa en esta idea. LP-DQ combina "tree-splitting" con la lógica de dos colas distribuidas que gestionan la resolución de la contienda en la solicitud de acceso y la transmisión de datos libre de colisiones. Los resultados demuestran que LP-DQ mejora LP-CTA y FSA en términos de retardo y eficiencia energética, LP-DQ no requiere conocer el tamaño de la red y se adapta sin problemas a cualquier cambio en el número de dispositivos. LP-DQ es conveniente cuando los mensajes transmitidos por cada dispositivo caben en un único slot de datos, sin embargo, si los dispositivos generan mensajes largos que requieren fragmentación, es mejor añadir un mecanismo de reserva para aumentar el rendimiento. En este sentido, el protocolo LPR-DQ se propone como una extensión de LP-DQ que incluye un mecanismo de reserva para permitir que cada dispositivo reserve el número de slots de datos según sea el número de fragmentos por mensaje. La segunda parte de la tesis está dedicada a la integración de la capa MAC con el uso de "Energy Harvesters". La variabilidad y las fluctuaciones de la energía capturada se consideran para el diseño de protocolos MAC de tipo "EH-aware" y se proponen tres métricas de rendimiento: la probabilidad de entrega, el "Data Delivery Ratio" y la eficiencia temporal. Los trabajos previos en redes de recolección de datos con EH se centran principalmente en DFSA. En esta tesis, el protocolo EH-CTA se propone como una adaptación de LP-CTA que tiene en cuenta el proceso de captura de energía. Los resultados muestran que EH-CTA supera DFSA si el umbral de energía para que un dispositivo se active está configurado correctamente. Además, mientras que en DFSA se necesita adaptar la longitud de trama de forma dinámica, EH-CTA utiliza una longitud de trama fija, facilitando así la escalabilidad y la sincronización. Por último, se proponen los protocolos EH-RDFSA y EH-DQ para escenarios en los que los datos deben ser fragmentados. EH-RDFSA es una combinación de RFSA y DFSA, y EH-DQ es una extensión de LPR-DQ.Aquesta tesi contribueix a resoldre dos dels reptes per al desplegament de xarxes M2M en escenaris de recol·lecció de dades per a l'Internet de les Coses: la gestió de l'accés al canal d'un nombre massiu de dispositius; i la necessitat d'extendre la vida de la xarxa. Per resoldre'ls es consideren dues estratègies complementàries. En primer lloc, es centra en el disseny, l'anàlisi i l'avaluació de protocols MAC que poden manegar transicions abruptes de trànsit i redueixen el consum d'energia. I en segon lloc, es considera l'ús de mecanismes de captura d'energia (Energy Harvesters, EH) per a oferir un temps de vida il·limitat de la xarxa. Amb aquesta finalitat, la segona part de la tesi es centra en el disseny i l'anàlisi de protocols MAC de tipus "EH-aware".Mentre que Frame Slotted-ALOHA (FSA) ha estat tradicionalment adoptat en aplicacions de recol·lecció de dades, els resultats mostren que FSA presenta problemes d'escalabilitat i sincronització quan augmenta la densitat de la xarxa. De fet, la longitud de trama de FSA s'ha d'ajustar segons sigui el nombre de dispositius, la qual cosa pot ser difícil d'estimar en xarxes amb un nombre elevat i dinàmic de dispositius. Per superar aquests problemes, en aquesta tesi es proposa un protocol d'accés aleatori basat en "tree-splitting" denominat Low Power Contention Tree-based Access (LP-CTA). En LP-CTA, la longitud de trama pot ser curta i constant, la qual cosa facilita la sincronització i proporciona millor escalabilitat.Mentre que LP-CTA utilitza paquets de dades per a la contenció, és possible utilitzar sol·licituds d'accés a mini-slots, on les col·lisions es resolen utilitzant "tree-splitting", i evitar la contenció a les dades. Atès que aquests mini-slots poden ser molt més curts que la durada d'un slot de dades, el rendiment de LP-CTA pot ser millorat. El protocol Low Power Distributed Queuing (LP-DQ) proposat en aquesta tesi es basa en aquesta idea. LP-DQ combina "tree-splitting" amb la lògica de dues cues distribuïdes que gestionen la resolució de la contenció en la sol·licitud d'accés i la transmissió de dades lliure de col·lisions. Els resultats demostren que LP-DQ millora LP-CTA i FSA en termes de retard i eficiència energètica, LP-DQ no requereix conèixer la mida de la xarxa i s'adapta sense problemes a qualsevol canvi en el nombre de dispositius.LP-DQ és convenient quan els missatges transmesos per cada dispositiu caben en un únic slot de dades, però, si els dispositius generen missatges llargs que requereixen fragmentació, és millor afegir un mecanisme de reserva per augmentar el rendiment. En aquest sentit, el protocol LPR-DQ es proposa com una extensió de LP-DQ que inclou un mecanisme de reserva per a permetre que cada dispositiu reservi el nombre de slots de dades segons sigui el nombre de fragments per missatge.La segona part de la tesi està dedicada a la integració de la capa MAC amb l'ús de "Energy Harvesters". La variabilitat i les fluctuacions de l'energia capturada es consideren per al disseny de protocols MAC de tipus "EH-aware" i es proposen tres mètriques de rendiment: la probabilitat d'entrega, el "Data Delivery Ratio" i l'eficiència temporal.Els treballs previs en xarxes de recol·lecció de dades amb EH se centren principalment en DFSA. En aquesta tesi, el protocol EH-CTA es proposa com una adaptació de LP-CTA que té en compte el procés de captura d'energia. Els resultats mostren que EH-CTA supera DFSA si el llindar d'energia perquè un dispositiu s'activi s'ajusta correctament. A més, mentre que a DFSA es necessita adaptar la longitud de trama de forma dinàmica, EH-CTA utilitza una longitud de trama fixa, facilitant així l'escalabilitat i la sincronització. Finalment, es proposen els protocols EH-RDFSA i EH-DQ per a escenaris en els quals les dades han de ser fragmentades. EH-RDFSA és una combinació de RFSA i DFSA, i EH-DQ és una extensió de LPR-DQ.Postprint (published version

Towards end-to-end security in internet of things based healthcare

Healthcare IoT systems are distinguished in that they are designed to serve human beings, which primarily raises the requirements of security, privacy, and reliability. Such systems have to provide real-time notifications and responses concerning the status of patients. Physicians, patients, and other caregivers demand a reliable system in which the results are accurate and timely, and the service is reliable and secure. To guarantee these requirements, the smart components in the system require a secure and efficient end-to-end communication method between the end-points (e.g., patients, caregivers, and medical sensors) of a healthcare IoT system. The main challenge faced by the existing security solutions is a lack of secure end-to-end communication. This thesis addresses this challenge by presenting a novel end-to-end security solution enabling end-points to securely and efficiently communicate with each other. The proposed solution meets the security requirements of a wide range of healthcare IoT systems while minimizing the overall hardware overhead of end-to-end communication. End-to-end communication is enabled by the holistic integration of the following contributions. The first contribution is the implementation of two architectures for remote monitoring of bio-signals. The first architecture is based on a low power IEEE 802.15.4 protocol known as ZigBee. It consists of a set of sensor nodes to read data from various medical sensors, process the data, and send them wirelessly over ZigBee to a server node. The second architecture implements on an IP-based wireless sensor network, using IEEE 802.11 Wireless Local Area Network (WLAN). The system consists of a IEEE 802.11 based sensor module to access bio-signals from patients and send them over to a remote server. In both architectures, the server node collects the health data from several client nodes and updates a remote database. The remote webserver accesses the database and updates the webpage in real-time, which can be accessed remotely. The second contribution is a novel secure mutual authentication scheme for Radio Frequency Identification (RFID) implant systems. The proposed scheme relies on the elliptic curve cryptography and the D-Quark lightweight hash design. The scheme consists of three main phases: (1) reader authentication and verification, (2) tag identification, and (3) tag verification. We show that among the existing public-key crypto-systems, elliptic curve is the optimal choice due to its small key size as well as its efficiency in computations. The D-Quark lightweight hash design has been tailored for resource-constrained devices. The third contribution is proposing a low-latency and secure cryptographic keys generation approach based on Electrocardiogram (ECG) features. This is performed by taking advantage of the uniqueness and randomness properties of ECG's main features comprising of PR, RR, PP, QT, and ST intervals. This approach achieves low latency due to its reliance on reference-free ECG's main features that can be acquired in a short time. The approach is called Several ECG Features (SEF)-based cryptographic key generation. The fourth contribution is devising a novel secure and efficient end-to-end security scheme for mobility enabled healthcare IoT. The proposed scheme consists of: (1) a secure and efficient end-user authentication and authorization architecture based on the certificate based Datagram Transport Layer Security (DTLS) handshake protocol, (2) a secure end-to-end communication method based on DTLS session resumption, and (3) support for robust mobility based on interconnected smart gateways in the fog layer. Finally, the fifth and the last contribution is the analysis of the performance of the state-of-the-art end-to-end security solutions in healthcare IoT systems including our end-to-end security solution. In this regard, we first identify and present the essential requirements of robust security solutions for healthcare IoT systems. We then analyze the performance of the state-of-the-art end-to-end security solutions (including our scheme) by developing a prototype healthcare IoT system

Advances in analytical models and applications for RFID, WSN and AmI systems

Experimentos llevados a cabo con el equipo de división de honor UCAM Volleyball Murcia.[SPA] Internet de las cosas (IoT) integra distintos elementos que actúan tanto como fuentes, como sumideros de información, a diferencia de la percepción que se ha tenido hasta ahora de Internet, centrado en las personas. Los avances en IoT engloban un amplio número de áreas y tecnologías, desde la adquisición de información hasta el desarrollo de nuevos protocolos y aplicaciones. Un concepto clave que subyace en el concepto de IoT, es el procesamiento de forma inteligente y autónoma de los flujos de información que se dispone. En este trabajo, estudiamos tres aspectos diferentes de IoT. En primer lugar, nos centraremos en la infraestructura de obtención de datos. Entre las diferentes tecnologías de obtención de datos disponibles en los sistemas IoT, la Identificación por Radio Frecuencia (RFID) es considerada como una de las tecnologías predominantes. RFID es la tecnología detrás de aplicaciones tales como control de acceso, seguimiento y rastreo de contenedores, gestión de archivos, clasificación de equipaje o localización de equipos. Con el auge de la tecnología RFID, muchas instalaciones empiezan a requerir la presencia de múltiples lectores RFID que operan próximos entre sí y conjuntamente. A estos escenarios se les conoce como dense reader environments (DREs). La coexistencia de varios lectores operando simultáneamente puede causar graves problemas de interferencias en el proceso de identificación. Uno de los aspectos claves a resolver en los RFID DREs consiste en lograr la coordinación entre los lectores. Estos problemas de coordinación son tratados en detalle en esta tesis doctoral. Además, dentro del área de obtención de datos relativa a IoT, las Redes de Sensores Inalámbricas (WSNs) desempeñan un papel fundamental. Durante la última década, las WSNs han sido estudiadas ampliamente de forma teórica, y la mayoría de problemas relacionados con la comunicación en este tipo de redes se han conseguido resolver de forma favorable. Sin embargo, con la implementación de WSNs en proyectos reales, han surgido nuevos problemas, siendo uno de ellos el desarrollo de estrategias realistas para desplegar las WSN. En este trabajo se estudian diferentes métodos que resuelven este problema, centrándonos en distintos criterios de optimización, y analizando las diferentes ventajas e inconvenientes que se producen al buscar una solución equilibrada. Por último, la Inteligencia Ambiental (AmI) forma parte del desarrollo de aplicaciones inteligentes en IoT. Hasta ahora, han sido las personas quienes han tenido que adaptarse al entorno, en cambio, AmI persigue crear entornos de obtención de datos capaces de anticipar y apoyar las acciones de las personas. AmI se está introduciendo progresivamente en diversos entornos reales tales como el sector de la educación y la salud, en viviendas, etc. En esta tesis se introduce un sistema AmI orientado al deporte que busca mejorar el entrenamiento de los atletas, siendo el objetivo prioritario el desarrollo de un asistente capaz de proporcionar órdenes de entrenamiento, basadas tanto en el entorno como en el rendimiento de los atletas. [ENG] Internet of Things (IoT) is being built upon many different elements acting as sources and sinks of information, rather than the previous human-centric Internet conception. Developments in IoT include a vast set of fields ranging from data sensing, to development of new protocols and applications. Indeed, a key concept underlying in the conception of IoT is the smart and autonomous processing of the new huge data flows available. In this work, we aim to study three different aspects within IoT. First, we will focus on the sensing infrastructure. Among the different kind of sensing technologies available to IoT systems, Radio Frequency Identification (RFID) is widely considered one of the leading technologies. RFID is the enabling technology behind applications such as access control, tracking and tracing of containers, file management, baggage sorting or equipment location. With the grow up of RFID, many facilities require multiple RFID readers usually operating close to each other. These are known as Dense Reader Environments (DREs). The co-existence of several readers operating concurrently is known to cause severe interferences on the identification process. One of the key aspects to solve in RFID DREs is achieving proper coordination among readers. This is the focus of the first part of this doctoral thesis. Unlike previous works based on heuristics, we address this problem through an optimization-based approach. The goal is identifying the maximum mean number of tags while network constraints are met. To be able to formulate these optimization problems, we have obtained analytically the mean number of identifications in a bounded -discrete or continuous- time period, an additional novel contribution of our work. Results show that our approach is overwhelmingly better than previous known methods. Along sensing technologies of IoT, Wireless Sensor Networks (WSNs) plays a fundamental role. WSNs have been largely and theoretically studied in the past decade, and many of their initial problems related to communication aspects have been successfully solved. However, with the adoption of WSNs in real-life projects, new issues have arisen, being one of them the development of realistic strategies to deploy WSNs. We have studied different ways of solving this aspect by focusing on different optimality criteria and evaluating the different trade-offs that occur when a balanced solution must be selected. On the one hand, deterministic placements subject to conflicting goals have been addressed. Results can be obtained in the form of Pareto-frontiers, allowing proper solution selection. On the other hand, a number of situations correspond to deployments were the nodes¿ position is inherently random. We have analyzed these situations leading first to a theoretical model, which later has been particularized to a Moon WSN survey. Our work is the first considering a full model with realistic properties such as 3D topography, propellant consumptions or network lifetime and mass limitations. Furthermore, development of smart applications within IoT is the focus of the Ambient Intelligence (AmI) field. Rather than having people adapting to the surrounding environment, AmI pursues the development of sensitive environments able to anticipate support in people¿s actions. AmI is progressively being introduced in many real-life environments like education, homes, health and so forth. In this thesis we develop a sport-oriented AmI system designed to improve athletes training. The goal is developing an assistant able to provide real-time training orders based on both environment and athletes¿ biometry, which is aimed to control the aerobic and the technical-tactical training. Validation experiments with the honor league UCAM Volleyball Murcia team have shown the suitability of this approach.[ENG] Internet of Things (IoT) is being built upon many different elements acting as sources and sinks of information, rather than the previous human-centric Internet conception. Developments in IoT include a vast set of fields ranging from data sensing, to development of new protocols and applications. Indeed, a key concept underlying in the conception of IoT is the smart and autonomous processing of the new huge data flows available. In this work, we aim to study three different aspects within IoT. First, we will focus on the sensing infrastructure. Among the different kind of sensing technologies available to IoT systems, Radio Frequency Identification (RFID) is widely considered one of the leading technologies. RFID is the enabling technology behind applications such as access control, tracking and tracing of containers, file management, baggage sorting or equipment location. With the grow up of RFID, many facilities require multiple RFID readers usually operating close to each other. These are known as Dense Reader Environments (DREs). The co-existence of several readers operating concurrently is known to cause severe interferences on the identification process. One of the key aspects to solve in RFID DREs is achieving proper coordination among readers. This is the focus of the first part of this doctoral thesis. Unlike previous works based on heuristics, we address this problem through an optimization-based approach. The goal is identifying the maximum mean number of tags while network constraints are met. To be able to formulate these optimization problems, we have obtained analytically the mean number of identifications in a bounded -discrete or continuous- time period, an additional novel contribution of our work. Results show that our approach is overwhelmingly better than previous known methods. Along sensing technologies of IoT, Wireless Sensor Networks (WSNs) plays a fundamental role. WSNs have been largely and theoretically studied in the past decade, and many of their initial problems related to communication aspects have been successfully solved. However, with the adoption of WSNs in real-life projects, new issues have arisen, being one of them the development of realistic strategies to deploy WSNs. We have studied different ways of solving this aspect by focusing on different optimality criteria and evaluating the different trade-offs that occur when a balanced solution must be selected. On the one hand, deterministic placements subject to conflicting goals have been addressed. Results can be obtained in the form of Pareto-frontiers, allowing proper solution selection. On the other hand, a number of situations correspond to deployments were the nodes¿ position is inherently random. We have analyzed these situations leading first to a theoretical model, which later has been particularized to a Moon WSN survey. Our work is the first considering a full model with realistic properties such as 3D topography, propellant consumptions or network lifetime and mass limitations. Furthermore, development of smart applications within IoT is the focus of the Ambient Intelligence (AmI) field. Rather than having people adapting to the surrounding environment, AmI pursues the development of sensitive environments able to anticipate support in people¿s actions. AmI is progressively being introduced in many real-life environments like education, homes, health and so forth. In this thesis we develop a sport-oriented AmI system designed to improve athletes training. The goal is developing an assistant able to provide real-time training orders based on both environment and athletes¿ biometry, which is aimed to control the aerobic and the technical-tactical training. Validation experiments with the honor league UCAM Volleyball Murcia team have shown the suitability of this approach.Universidad Politécnica de CartagenaPrograma de doctorado en Tecnología de la Información y de las Comunicacione