Andreas Loeffler

Realization of a CDMA-based RFID System Using a Semi-active UHF Transponder

RFID systems may increase the efficiency of logistic systems, e.g., inventory of stocks. Unfortunately, present existing systems come fast to their limits if a great amount of RFID transponder must be inventoried in very short time, as the channel access method of current RFID systems is Time Division Multiple Access. To shorten the inventory process, this work shows a first realization of an RFID-based semi-active UHF transponder using a Code Division Multiple Access method. The work concentrates on the uplink channel (tag to reader) that covers the transponders backscattered signals. This channel access method enables simultaneous transfer of data, meaning that all transponder in the field may respond at the same time within the same frequency band. The data transfer realized for the uplink channel, uses a certain set of orthogonal spreading sequences (modified Gold codes) being different for every transponder. The RFID reader used in this work despreads the backscattered signals and decodes the data of the different transponder. Briefly, this work shows, in principle, the opportunity for a simultaneous data transfer on the uplink channel in RFID systems, which in turn may shorten very much the time for a complete inventory round.

A multi-purpose RFID reader supporting indoor navigation systems

In this paper we introduce an UHF-RFID reader system built to serve as a multi-purpose reader for UHF-RFID applications. The structure of the reader itself is highly flexible to be able to include several standards. The intended use of the reader, however, consists in the support of navigation systems for the indoor environment. Assuming that arbitrarily distributed RFID tags, containing their exact positions given in latitude, longitude and elevation, are read out by the reader, the system is able to achieve the tags positions. In that case, the reader is able to evaluate and forward the readout positions in order to notify a superior navigation system of the estimated position, obtained from the RFID tags. This will lead to a more robust navigation system being able to navigate even in a high-grade multipath environment. Anyway, this paper concentrates more on technical terms concerning the reader system, including signal and spectrum analysis.

Using RFID-capable cell phones for creating an extended navigation assistance

This paper offers an RFID-based indoor navigation application which utilizes cell phones with an RFID extension and distributed RFID tags fixed to interior equipment. This combination creates a special navigation environment which helps pedestrians to orient oneself in new respectively unknown environments. Therefore, each RFID tag contains information about the current position, location or an unknown environment. Thus, the current position can be determined, which is the basic for navigation. A further advantage of this application is the availability of additional graphical data stored on the RFID tags. This additional graphical data contains global information about the indoor environment and also local graphical information about the near environment of the RFID tag. This yields to an RFID-based navigation system, that not only shows the current position but also the near environment surrounding that specific location. Therefore, this systems grants navigation assistance by leading the user step-by-step or rather tag-by-tag to the final destination.

Localizing with Passive UHF RFID Tags Using Wideband Signals

Localization of positions and detection of objects is a key aspect in today’s applications and, although the topic exists a while ago, it is still under ongoing research. The introduction of global navigation satellite systems (GNSS), particularly GPS [1], and its improvements with accuracies down to a few meters, was a huge step towards ubiquitous localization [2, 3]. This is almost valid for outdoor environments, whereas indoor localization is still a challenging issue [4, 5]. The reason for that is the demanding, dynamic indoor environment, causing severe multipath fading, leading to hard predictable propagation models thus influencing time, power and phase measurements. However, in the past, much effort has been put into designing high accurate indoor localization systems, including technologies like ultrasonic sound, infrared light, Wi-Fi, Bluetooth, ZigBee, cellular mobile communication (GSM, UMTS), ultrawideband and RFID just to mention a few of them. Despite all the effort, there is no outstanding technology comprising all indoor localization contingencies as every technology in use has its advantages and disadvantages regarding accuracy, availability, complexity and costs.

Localizing passive UHF RFID tags with wideband signals

Applications using localization of passive UHF RFID tags include, among others, indoor and assistant navigation (e.g., together with GPS), logistics, etc. This work shows a method to determine the distance between a tag and a reader by using passive UHF RFID tags and low power wideband signals. The passive UHF RFID tag is emulated through an antenna with varying load impedances. The work shown in this paper presents some first experimental results of such a ranging system.

An UHF RFID reader for cell phones

This paper presents a mobile, cell phone-based UHF RFID reader. The UHF reader is based on a single chip solution with few external components, currently working as USB client at the cell phones USB host connection. Therefore, our work describes a fully functional UHF RFID reader connected to the cell phone, providing power and communication capabilities.