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

Location estimation in a 3D environment using radio frequency identification tags

RFID tag location estimation in a 3D environment is investigated. The location of the tag with unknown coordinates can be estimated with certain accuracy. However, accuracy can be improved using the knowledge based on measurement of additional reference tags with known location. This thesis studies the mathematical formulation and practical realization of location sensing using RFID tags. Deviating from the standard use of RFID technology which employs one tag reader to identify the presence of tag, here multiple tag readers with known location are used to estimate the physical location of an individual tag, with/without the help of few reference tags with known locations. Mathematical model of this concept has been developed based on distance variations in terms of signal strength. Experimental approach with limited range passive tags has been carried out. Since the range of the RFID system was limited only to a few inches, signal strength variations were insignificant. Instead, time domain measurements with the help of an external antenna were conducted. The composite signal width including of the wake up signal of the interrogator, travel time between the interrogator and tag, and the tag\u27s response was measured and quantified. It was observed that the width of the signal was proportional to the distance between the tag reader and the tag. It was noticed that the use of four RFID tag readers yielded fairly accurate results to identify the location the tag based on the mathematical formulation developed here. Additionally, concept of trilateration has also been extended for tracking the tag of unknown location without the use of reference tags. Archival data set corresponding to all tag location due to four different tag readers was compiled. The unknown tag was probed with four tag readers and matching the data to the archival data set yielded unique and accurate results for its unknown location. It was demonstrated that both approaches were proved to be cost-effective techniques and estimation of the location of a specific tag has been achieved with sufficient accuracy

Building efficient wireless infrastructures for pervasive computing environments

Pervasive computing is an emerging concept that thoroughly brings computing devices and the consequent technology into people\u27s daily life and activities. Most of these computing devices are very small, sometimes even invisible , and often embedded into the objects surrounding people. In addition, these devices usually are not isolated, but networked with each other through wireless channels so that people can easily control and access them. In the architecture of pervasive computing systems, these small and networked computing devices form a wireless infrastructure layer to support various functionalities in the upper application layer.;In practical applications, the wireless infrastructure often plays a role of data provider in a query/reply model, i.e., applications issue a query requesting certain data and the underlying wireless infrastructure is responsible for replying to the query. This dissertation has focused on the most critical issue of efficiency in designing such a wireless infrastructure. In particular, our problem resides in two domains depending on different definitions of efficiency. The first definition is time efficiency, i.e., how quickly a query can be replied. Many applications, especially real-time applications, require prompt response to a query as the consequent operations may be affected by the prior delay. The second definition is energy efficiency which is extremely important for the pervasive computing devices powered by batteries. Above all, our design goal is to reply to a query from applications quickly and with low energy cost.;This dissertation has investigated two representative wireless infrastructures, sensor networks and RFID systems, both of which can serve applications with useful information about the environments. We have comprehensively explored various important and representative problems from both algorithmic and experimental perspectives including efficient network architecture design and efficient protocols for basic queries and complicated data mining queries. The major design challenges of achieving efficiency are the massive amount of data involved in a query and the extremely limited resources and capability each small device possesses. We have proposed novel and efficient solutions with intensive evaluation. Compared to the prior work, this dissertation has identified a few important new problems and the proposed solutions significantly improve the performance in terms of time efficiency and energy efficiency. Our work also provides referrable insights and appropriate methodology to other similar problems in the research community

DISTRIBUTED PHASED ARRAY ANTENNAS IN WIDE AREA RFID

Ultra High Frequency (UHF) Radio Frequency Identification (RFID) has gained importance over the past two decades in many applications such as stock management, asset tracking and access control. For wide area applications, Distributed Antenna Systems (DAS) have been used to obtain good coverage with few antennas by making use of multiple spatially distributed antennas and phase dithering. This implements a far-field beamforming that maximises the instantaneous power at a tag. Separately, phased array antennas have also been used to increase the read range by increasing the effective field of view of an antenna and overcoming multipath fading through beam steering. This dissertation explores a combination of both approaches to improve RFID read ranges in wide interrogation zones. Distributed antenna arrays are explored in the context of delivering high tag detection probabilities in a multi-cell RFID system, while maximising inter-antenna separations. A Distributed Antenna Array System (DAAS) is designed and shown to be capable of providing comparable performance to a fixed DAS system with fewer antennas. The properties of the system are further studied and its upper performance limit is explored by modelling a hypothetical perfectly steerable antenna array. The concept of using perfectly steerable arrays is further explored to propose a cell-less RFID system, in which cell allocation in wide area RFID is replaced with a tag location-based interrogation requiring the global reader antenna population to be used for interrogation of all tags, leading to significant potential increases in inter-antenna separation, and consequently good coverage with fewer antennas. It is also argued that this system leads to the avoidance of complex reader anti-collision policies, since only a single central reader is now required. Finally, the design of a wide-scan-angle antenna array is presented as a compromise solution for perfectly steerable antennas, whist still keeping the desired property of being flat panel. A 3D RFID multi-antenna model is presented and used for simulating and analysing the various described systems and for system planning

On a wildlife tracking and telemetry system : a wireless network approach

Includes abstract.Includes bibliographical references (p. 239-261).Motivated by the diversity of animals, a hybrid wildlife tracking system, EcoLocate, is proposed, with lightweight VHF-like tags and high performance GPS enabled tags, bound by a common wireless network design. Tags transfer information amongst one another in a multi-hop store-and-forward fashion, and can also monitor the presence of one another, enabling social behaviour studies to be conducted. Information can be gathered from any sensor variable of interest (such as temperature, water level, activity and so on) and forwarded through the network, thus leading to more effective game reserve monitoring. Six classes of tracking tags are presented, varying in weight and functionality, but derived from a common set of code, which facilitates modular tag design and deployment. The link between the tags means that tags can dynamically choose their class based on their remaining energy, prolonging lifetime in the network at the cost of a reduction in function. Lightweight, low functionality tags (that can be placed on small animals) use the capabilities of heavier, high functionality devices (placed on larger animals) to transfer their information. EcoLocate is a modular approach to animal tracking and sensing and it is shown how the same common technology can be used for diverse studies, from simple VHF-like activity research to full social and behavioural research using wireless networks to relay data to the end user. The network is not restricted to only tracking animals – environmental variables, people and vehicles can all be monitored, allowing for rich wildlife tracking studies

Developing Biosensor Technology to Monitor Biofilm Formation on Voice Prosthesis in Throat Cancer Patients Following Total Laryngectomy

Voice prostheses (used to replace an excised larynx in laryngectomy patients) are often colonised by the yeast Candida albicans, yet no monitoring technology for C. albicans biofilm growth until these devices fail. With the current interest in smart technology, understanding the electrical properties of C. albicans biofilm formation is necessary. There has been great interest in Passive Radio Frequency Identification (RFID) for use with implantable devices as they provide a cost-effective approach for sensing. The main drawback of RFID sensors is the need to overcome capacitive loading of human tissue and, thus, low efficiency to produce a high read range sensor design. This is further complicated by the size restriction on any RFID design to be implemented within a voice prosthesis as this medical device is limited to less than 3 cm in overall size. In order to develop such a voice prosthesis sensor, we looked at three separate aspects of C. albicans colonisation on medical devices within human tissue. To understand if it is possible to detect changes within a moist environment (such as the mouth), we developed a sensor capable of detecting minute dielectric changes (accuracy of ± 0.83 relative permittivity and ± 0.05 S·m-1 conductivity) within a closed system. Once we understood that detection of dielectric changes within a liquid solution were possible, to overcome human tissue capacitive loading of RFID sensors. Adjusting backing thickness or adding a capacitive shunt into the design could limit this tissue effect and even negate the variability seen between human tissues. Without developing these methods, implementation of any RFID device would be difficult as human tissue variability would not be compensated for properly. Finally, biofilm growth in terms electrical properties. As C. albicans biofilm matures, there is a loss in capacitance (the biofilm becomes increasingly hydrophobic) prior to 24 hours after which the biofilm thickness shifts the resonance leading to a slow gain in capacitance. Understanding all of these aspects allowed us to develop two final voice prosthesis sensors producing read ranges above 60 cm and 10 cm within a tissue phantom. Ultimately, this showed the possibility of developing cost-effective passive RFID sensor technology for monitoring microbial biofilm formation within human tissue, leading to more effective real-time clinical care