Fabian Kirsch

UHF RFID Localization Based on Synthetic Apertures

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 methods 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.

A novel method for UHF RFID tag tracking based on acceleration data

Options for RFID tag tracking and localization are an essential asset for future high performance RFID reader systems. A reader with long reading range, high reading rate and multi-tag capability should be able to assist the user to find / retrieve tags, to create spatial object maps and to restrict the reading range to specific regions of interest. In this paper we introduce a novel method for RFID tag tracking with a moving - for example handheld - reader. An inertial measurement unit (IMU) is used to characterize the handheld trajectory. Contrary to approaches where IMU locations are reconstructed via double integration of the acceleration data, our novel technique only uses acceleration data without knowledge of the actual antenna locations. Inexpensive, standard inertial sensors can be used in this approach, and the usual drift and offset issues associated with IMU-based positioning are avoided. Parallel to the IMU acceleration data, the phase of the backscattered RFID signal is input. Double differentiation of the signal phase yields a second acceleration data set. By comparing the IMU and the RFID signal phase acceleration data, the direction of arrival of the RFID signal is estimated using a quasi-spatial optimal filter. This paper introduces the novel RFID tracking approach and illustrates its capability with numerical simulations and experimental results. This novel approach is a simple, yet promising, solution which can be implemented in any handheld reader and will improve its functionality considerably.

Hybrid RFID system-based pedestrian localization: A case study

Localization systems using RFID - especially passive RFID - are coming increasingly under the spotlight. Passive RFID has a relatively small sensing range compared to other radio-frequency-based localization techniques. Therefore in practice the deployed tags may not cover the whole scene of interest. Additionally, in the area of pedestrian localization, the unpredictable movement of pedestrians makes a complete RFID tag coverage extremely difficult. This paper introduces a hybrid RFID localization system used for indoor pedestrians to overcome the coverage shortfall associated with passive RFID tags. Two extra sources are used to assist the RFID system: local INS sensors and ZigBee nodes. A particle filter serves as a fusion framework. A test scenario was built with 220 RFID tags and 8 ZigBee nodes deployed in a museum. Different algorithms were evaluated in this deployment. The results show that the hybrid approach produces robust localization even with a low number of tags.

Phase based multi carrier ranging for UHF RFID

The different methods to process phase measurement data of a MFCW ranging system with their characteristics are well suited to be used for UHF RFID ranging. Our measurements show that ranging ISO 18000-6C UHF RFID tags under FCC regulations is possible in outdoor conditions despite the limited bandwidth. Our next steps will be to further compare the robustness of the algorithms and to conduct measurements in multipath environments. Additionally we will combine this approach with other localization techniques. Using multiple antennas or synthetic apertures, this approach can help to increase the radial resolution significantly.

Precise local-positioning for autonomous situation awareness in the Internet of Things

This paper reviews different wireless local positioning principles and explains the interaction between local positioning and the Internet of Things (IOT). The principle, performance and use of recent local positioning systems in the context of the IOT are shown in detail for typical applications. The first application is the accurate real-time localization of transportation vehicles using local positioning radar. The second application is the loading state characterization of goods in the proximity of a forklift enabling fully automated warehouse management. The third application is the dynamic localization of UHF-RFID tags with a handheld reader, which provides helpful augmented reality for logistics personnel. The final application is the real-time localization of tools for production monitoring. The developed ultrawideband (UWB) locating system is based on a pulsed frequency modulated continuous wave (FMCW) radar principle. By using assisting inertial sensors and advanced fusion algorithms, highly accurate 3D localization was achieved even in complex industrial environments with dense multipath channels and shadowing.

A wireless crane to vessel locating system for sea swell compensation

Sea swell causes significant risk in transferring people and material to offshore constructions and oftentimes hamper the accessibility completely. The weather window where a construction is accessible can be enlarged notably if a crane is equipped with a sea swell compensation system. For a crane to vessel swell compensation system it is required to measure the 3D position of the crane load handling device relative to the deck of ship precisely, reliably and in real-time. In this paper a novel wireless crane to vessel locating system is introduced. Several secondary radar units that are mounted on the ship deck are measuring the distance to a responder unit attached to the crane boom. The 3D localization is based on a fusion of secondary radar distance measurements and the data from an inertial sensor platform. The fusion is done by a quaternion based extended Kalman filter which implements both multilateration and strapdown inertial navigation techniques. Real measurement data acquired with the inertial platform on a ship and radar data measured with the realized local positioning radar onshore are fed in a PC based simulation of the complete system. The real data simulations prove that the developed real time locating system provides the required position information precisely and reliably. By this it is shown that the novel wireless locating system is well suited for sea swell compensation equipment.

Optimization of fusion algorithm for hybrid pedestrian localization and navigation

Hybrid pedestrian localization based on multiple data sources is becoming more and more popular. Nevertheless, accurate and reliable pedestrian localization is still a challenge due mainly to their unpredictable movement. For some applications such as interactive museum guidance unpredictable pedestrian movement is a major obstacle to accurate localization. In this paper we introduce a novel fusion algorithm using best-neighbor rating. The algorithm reduces the accumulated error originating from unreliable sensor measurements and increases the efficiency by only evaluating the nearby cells of the last estimated position. Experimental results show that a mean error of less than 1.5 M is achievable in real-world scenarios.

Analytical study about the impact of multipath propagation on UHF-RFID ranging techniques

Given the narrow bandwidth of UHF-RFID it is not possible to separate the different signal paths apart. In this paper the SNR was derived, necessary for any nonlinear super-resolution algorithms. As long as these SNR levels are not met, any evaluation method will give a weighted mean of all the individual paths that exist in the perceived channel. Evaluation methods that use only one of “RSSI” and “phase” will even be worse. In order to open the possibilities of multipath resistant single-antenna ranging to the field of UHF-RFID applications new regulations or technologies with greater bandwidths are unavoidable.

Application of the Principal Component Analysis for acceleration based UHF RFID tag tracking

An algorithm for AoA estimation of UHF RFID tags, based on an acceleration defined synthetic aperture is derived with the aid of the Principal Component Analysis. It gives an analytical solution for the tag direction and requires significantly less computational effort than comparable algorithms while performing nearly as good as the benchmark algorithm. Handheld tracking systems using the proposed algorithm could therefore be implemented with significantly higher cost and power efficiency.