Reading ranges are being extended in the wake of recent advances in UHF radio frequency identification (RFID) systems, and with the advent of larger reading ranges, tag localization has moved into the spotlight. Recently, we introduced a new UHF RFID tag localization technique. The proposed method is based on phase measurements taken along a synthetic aperture. A holographic image is calculated based on the scanned phase values. The image represents the spatial probability density function for the actual tag location. This paper presents this innovative method in detail. Simulations that illustrate the effect of the given trajectory are included. Extensive measurements obtained in a reflective lab environment are presented. We discuss the method's effectiveness with respect to measurement errors, antenna phase center distortions, and the available phase information. The results show the potential practical applications for the method in moving reader antennas, such as handheld readers or readers mounted on vehicles like forklifts or mobile robotic systems.

In this paper a method for holographic localization of passive UHF-RFID transponders is presented. It is shown how persons or devices that are equipped with a RFID reader and that are moving along a trajectory can be enabled to locate tagged objects reliably. The localization method is based on phase values sampled from a synthetic aperture by a RFID reader. The calculated holographic image is a spatial probability density function that reveals the actual RFID tag position. Experimental results are presented which show that the holographically measured positions are in good agreement with the real position of the tag. Additional simulations have been carried out to investigate the positioning accuracy of the proposed method depending on different distortion parameters and measuring conditions. The effect of antenna phase center displacement is briefly discussed and measurements are shown that quantify the influence on the phase measurement.

In this paper, a closed-form expression for the ranging uncertainty of a primary frequency-modulated continuous-wave (FMCW) radar is introduced. In addition to basic system parameters also the phase noise profile of the transceiver serves as an input for this novel approach. On the signal processing side, phase noise range correlation effects are taken into account and an estimate for the ranging uncertainty is deduced. Thus, the influence of phase noise on the system performance in terms of precision can be directly predicted. For support of the theory, Monte-Carlo simulations were conducted. Measurement results acquired with a 77 GHz radar system are in good agreement with the theory.

Radiofrequency identification (RFID) has penetrated logistics, manufacturing, production, ticketing, access control, baggage tagging and various other areas of our daily life [1]. RFID technology has experienced tremendous growth and development since its humble beginnings back in the 1940s [2]. These remarkable technical advances have resulted in enhanced performance and novel application areas, which in turn stimulate new needs and spawn exciting new research initiatives. A current hot research topic in the RFID field is RFID localization.

This paper presents an inverse synthetic aperture radar approach for localizing standard UHF RFID transponders. The proposed method is a powerful option to estimate the positions of tags that pass RFID gates or read points. A priori information about the relative transponder trajectory, such as the speed of a conveyor belt or a trajectory created by a robotic arm or rotary table, is used to generate an inverse synthetic aperture. Sampled phase data from RFID signals which are backscattered to single or multiple antennas combined with the information on the relative RFID tag trajectory are used to reconstruct the tag's absolute trajectory. The paper describes basic properties of synthetic apertures in RFID systems and methods of evaluating beam patterns based on array beam steering theory. Simulations of a conveyor belt scenario and test data acquired from an industrial rotary table transporting tagged objects are described. The experimental results prove that our novel method enables robust localization of moving RFID tags even in a severe multipath environment.

We present a frequency-modulated continuous-wave secondary radar concept to estimate the offset in time and in frequency of two wireless units and to measure their distance relative to each other. By evaluating the Doppler frequency shift of the radar signals, the relative velocity of the mobile units is measured as well. The distance can be measured with a standard deviation as low as 1 cm. However, especially in indoor environments, the accuracy of the system can be degraded by multipath transmissions. Therefore, we show an extension of the algorithm to cope with multipath propagation. We also present the hardware setup of the measurement system. The system is tested in various environments. The results prove the excellent performance and outstanding reliability of the algorithms presented.