Papers by Antonis Dimitriou
Hyperbolic Positioning and Tracking of Moving UHF-RFID Tags by Exploiting Neural Networks
2022 16th European Conference on Antennas and Propagation (EuCAP), Mar 27, 2022
Phase ReLock - Localization of RFID Tags by a Moving Robot
European Conference on Antennas and Propagation, Mar 1, 2019
In this work, we propose a prototype method for the localization of RFID tags, by deploying RFID ... more In this work, we propose a prototype method for the localization of RFID tags, by deploying RFID equipment on a robotic platform. The constructed robot is capable to perform Simultaneous Localization (of its own position) and Mapping of the environment and then locate the RFID tags around its path. The proposed method is based on properly treating the measured phase of the backscattered signal by each tag at the reader’s antenna, located on top of the robot. More specifically, the measured phase samples are reconstructed, such that the 2π discontinuities are eliminated. This allows for the formation of an optimization problem, which can be solved rapidly by standard methods. The proposed method is experimentally compared against the most accurate reported method in prior-art and the same accuracy is preserved. However, the problem is solved more than one order of magnitude faster, allowing for the applicability of the method in real-time inventorying and localization.
This work studies frequency allocation in 802.11s mesh wireless networks, employing muti-radio te... more This work studies frequency allocation in 802.11s mesh wireless networks, employing muti-radio terminals and directive antennas. The network targets city-wide deployment and connects critical water tanks, storage reservoirs and pumping stations. The objective is to offer frequency planning with minimum remaining interference between the network terminals, under stringent and practical constraints, including a) long distances, on the order of 4 − 5 kilometers, b) radio terminals with broad beamwidths that serve multiple destinations, c) need for different frequency channels among different radio interfaces at the same terminal and d) limited number of frequency channels and transmission power. Practical centralized algorithms are provided for connectivity, conflict graph and frequency channel assignment, considering all constraints. It is shown that frequency planning under such stringent constraints is feasible.
Robotics Meets RFID for Simultaneous Localization (of Robots and Objects) and Mapping ( SLAM ) – A Joined Problem
Design, Analysis, and Performance Evaluation of a UHF RFID Forward-Link Repeater
IEEE journal of radio frequency identification, Jun 1, 2020
IEEE Transactions on Antennas and Propagation, Mar 1, 2007
A new propagation prediction model, suitable for an antenna placed below rooftop level in an urba... more A new propagation prediction model, suitable for an antenna placed below rooftop level in an urban environment is presented. It is shown that the contribution of various arriving rays at a specific location can be well approximated by a set of geometric progressions. Each progression is associated with a source. Then, estimation is delivered as soon as the leading term and the ratio have been computed. The ratio reflects the significance of secondary ray-paths. It depends on the geometry and the electromagnetic properties of the materials within the "street canyon." In contrast to typical semi-deterministic approaches, detailed information on the power, the time of arrival and the angle of arrival of all significant components is delivered. Consequently, wideband characterization of the environment is accomplished at short running-time. High accuracy is experimentally verified in a typical urban configuration.
Target Localization by Mobile Handheld UHF RFID Reader and IMU
IEEE journal of radio frequency identification, 2022
Device-free Human Tracking Exploiting Phase Disturbances and Particle Filters
Designing Limited-EIRP, Long-distance Links for Water Management Networks Using Polarization Diversity and Redundant Routing Paths
Journal of Intelligent and Robotic Systems, Sep 15, 2020
Robot localisation is predominantly resolved via parametric or non-parametric probabilistic metho... more Robot localisation is predominantly resolved via parametric or non-parametric probabilistic methods. The particle filter, the most common non-parametric approach, is a Monte Carlo Localisation (MCL) method that is extensively used in robot localisation, as it can represent arbitrary probabilistic distributions, in contrast to Kalman filters, which is the standard parametric representation. In particle filters, a weight is internally assigned to each particle, and this weight serves as an indicator of a particle's estimation certainty. Their output, the tracked object's pose estimate, is implicitly assumed to be the weighted average pose of all particles; however, we argue that disregarding low-weight particles from this averaging process may yield an increase in accuracy. Furthermore, we argue that scan-matching, treated as a prosthesis of (or, put differently, fit in tandem with) a particle filter, can also lead to better accuracy. Moreover, we study the effect of feeding back this improved estimate to MCL, and introduce a feedback method that outperforms current state-of-the-art feedback approaches in accuracy and robustness, while alleviating their drawbacks. In the process of formulating these hypotheses we construct a localisation pipeline that admits configurations that are a superset of state-of-the-art configurations of tandem combinations of particle filters with scan-matching. The above hypotheses are tested in two simulated environments and results support our argumentation.
Trajectory Planning of a Moving Robot Empowers 3D Localization of RFID Tags With a Single Antenna
IEEE journal of radio frequency identification, Dec 1, 2020
In this work, we present a method for 3D localization of RFID tags by a reader-equipped robot wit... more In this work, we present a method for 3D localization of RFID tags by a reader-equipped robot with a single antenna. The robot carries a set of sensors, which enable it to create a map of the environment and locate itself in it (Simultaneous Localization and Mapping - SLAM). Then we exploit the collected phase measurements to localize large tag populations in real-time. We show that by forcing the robot to move along non-straight trajectories, thus creating non-linear synthetic apertures, the circular ambiguity of the possible tag’s locations is eliminated and 3D localization is accomplished. A reliability metric is introduced, suitable for real-time assessment of the localization error. We investigate how the curvature of the robot’s trajectory affects the accuracy under varying multipath conditions. It is found that increasing the trajectory’s slope and number of turns improves the accuracy of the method. We introduce a phase model that accounts for the effects of multipath and derive the closed form expression of the resultant’s phase probability density function. Finally, the proposed method is extended when multiple antennas are available. Experimental results in a “multipath-rich” indoor environment demonstrate a mean 3D error of 35cm, achieved in a few seconds.
IEEE journal of radio frequency identification, Dec 1, 2019
In this paper, we propose a new method for the localization of RFID tags, by deploying off-the-sh... more In this paper, we propose a new method for the localization of RFID tags, by deploying off-the-shelf RFID equipment on a robotic platform. The constructed robot is capable to perform Simultaneous Localization (of its own position) and Mapping (SLAM) of the environment and then locate the RFID tags around its path. The proposed method is based on properly treating the measured phase of the backscattered signal by each tag at the reader's antenna, located on top of the robot. More specifically, the measured phase samples are reconstructed, such that the 2π discontinuities are eliminated (phase-unwrapping). This allows for the formation of an optimization problem, which can be solved rapidly by standard methods. The proposed method is experimentally compared against the SAR/imaging methods, which represent the accuracy benchmark in prior-art, deploying off-the-shelf equipment. It is shown that the proposed method solves exactly the same problem as holographic-imaging methods, overcoming the grid-density constraints of the latter. Furthermore, the problem, being calculations-grid-independent, is solved orders of magnitude faster, allowing for the applicability of the method in real-time inventorying and localization. It is also shown that the state-of-the-art SLAM method, which is used for the estimation of the trace of the robot, also suffers from errors, which directly affect the accuracy of the RFID localization method. Deployment of reference RFID tags at known positions, seems to significantly reduce such errors.
Passive UHF-RFID Hyperbolic Positioning of Moving Tags by Exploiting Neural Networks
IEEE journal of radio frequency identification, 2022
In this paper a maximum likelihood estimator of the locations of passive RFID tags is presented, ... more In this paper a maximum likelihood estimator of the locations of passive RFID tags is presented, exploiting the Received Signal Strength Information (RSSI) collected at the reader. The reader-antenna is fixed on a moving cart and collects RFID data in the area of interest. Locations of the reader-antenna and of the target-objects are obtained by the RSSI of "reference" tags placed at known positions. The proposed method can be applied using commercial RFID equipment. Measurements were conducted in an office environment; mean error of 25cm with standard deviation equal to 12,4cm is recorded. Localization accuracy can be further improved by increasing the density of the "reference" tags and the number of reader antennas.
Lane Keeping through RFID
Localization, Tracking and Following a Moving Target by an RFID Equipped Robot
In this paper, we present a prototype algorithm for tracking and following a moving target throug... more In this paper, we present a prototype algorithm for tracking and following a moving target through RFID technology by a robot. The robot is equipped with two front facing antennas, which collect phase measurements of the tag’s modulated signal. We consider a direction-finding algorithm, based on particle filter theory, which exploits the phase-measurements to assign weights to the particles. The proposed track-and-follow robot is successfully tested in a laboratory environment and will be deployed inside a museum.
Tag Localization by Handheld UHF RFID Reader and Optical Markers
Industrial Gen2 RFID tags are limited by the tag's RF energy harvesting sensitivity, requiring re... more Industrial Gen2 RFID tags are limited by the tag's RF energy harvesting sensitivity, requiring relatively strong signals that impinge on the tag's antenna. Prior art has proposed dense reader antenna networks, that effectively bring the illuminating antenna closer to the tag, using either networks of RF cables, multiplexers and RF amplifiers or custom RF front-ends, wired to a baseband processor or even custom wireless RF front ends with proprietary protocols. This work distributes Gen2 operation and proposes multistatic networks of commodity, low-cost, software defined radios (SDR), connected over the (nowadays omnipresent) Ethernet. Thus, this work puts forth distributed reception of Gen2 RFID with potentially reduced (installation) cost. Bit error rate (BER)-optimal coherent and near-optimal noncoherent, linear complexity Miller sequence detection are tested, adhering to real time processing constraints. Experimental results demonstrate that under real time carrier frequency offset estimation with phased-lock loop (PLL), Gen2 RFID tags can be detected reliably, without rate-limiting preamble pilot bits, while more than one distributed SDR transmitters can boost area coverage. Multistatic setups allow for higher probability the tag antenna will be found closer to sufficiently strong illuminating field, overcoming the limitations of existing RF energy harvesting technology. Hopefully, this work will spark interest towards the convergence of Gen2 RFID with (current) Ethernet or (future) cellular telephony industry.
Real-Time Global Localization of a Mobile Robot by Exploiting RFID Technology
IEEE journal of radio frequency identification, 2023
Design and Fabrication of a Compact, Low-Cost UHF-RFID Repeater, Exploiting Circular Cross-Polarization
IEEE journal of radio frequency identification, Mar 1, 2021
In this article we aim to increase the range of commercial passive UHF RFID technology. We propos... more In this article we aim to increase the range of commercial passive UHF RFID technology. We propose a prototype forward-link repeater, which consists of a pair of antennas, a band pass filter, an RF power limiter and a low-noise amplifier (LNA). Initially, we focus on the design of the two antennas with inverse direction of circular polarization (CP), so that sufficient decoupling is ensured, while adhering to the following constraints: <italic>i</italic>) the input antenna is circularly polarized to maximize the gain towards the reader’s antenna, <italic>ii</italic>) the output antenna is circularly polarized to improve the probability of successful tag reception, given the expected randomness in the tag’s orientation, <italic>iii</italic>) the volume of the entire structure is kept small. Then, we present the achieved range improvement of the proposed repeater in two applications: <inline-formula> <tex-math notation="LaTeX">${a}$ </tex-math></inline-formula>) a fixed installation, where the reader successfully identified passive RFID tags from 60m and <inline-formula> <tex-math notation="LaTeX">${b}$ </tex-math></inline-formula>) by placing the repeater on top of an autonomous robot, to provide power in distant battery-less RFID tags, while the robot randomly moves inside a large area. The robotic-repeater prototype achieved remarkable performance, inventorying distant passive RFID tags, under Non-Line-Of-Sight (NLOS) conditions with the reader, exploiting the robot’s mobility for fading-mitigation, combined with increased incident power from the repeater.
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Papers by Antonis Dimitriou