Václav Navrátil

Czech Technical University in Prague

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Co-Authors

Josef Krška

Czech Technical University in Prague

F. Vejražka

Czech Technical University in Prague

Marco Leone

Otto-von-Guericke University Magdeburg

Zoltán Koppányi

The Ohio State University

Graeme E. Smith

Johns Hopkins University Applied Physics Laboratory

Charles Toth

The Ohio State University

J. Landon Garry

Johns Hopkins University Applied Physics Laboratory

Dorota A. Grejner‐Brzezinska

The Ohio State University

Andrew O’Brien

Indiana University – Purdue University Indianapolis

Haowei Xu

Massachusetts Institute of Technology

Cooperative Institutions

Czech Technical University in Prague

The Ohio State University

Brno University of Technology

Johns Hopkins University Applied Physics Laboratory

California Institute of Technology

Ohio University

Universidade Federal do Paraná

VSB - Technical University of Ostrava

University of Defence

Technical museum in Brno

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Improving UWB Positioning Accuracy by Fusion With Pedestrian Dead-Reckoning

Josef Krška Václav Navrátil

Ultra-wide Band (UWB) positioning systems are a system of choice for indoor positioning. Though UWB is more resilient against multipath propagation, the positioning accuracy can still be hindered in its presence. The positioning accuracy and availability can be improved by combination with other sensors, typically inertial ones. In the case of pedestrian positioning the use of a dead-reckoning system, which uses the inertial data from a smartphone, may be advantageous. In this paper we propose the use of Extended Kalman filtering for the data fusion of UWB and STEP system, which detects the user making steps and estimate the step-length from the vertical acceleration of the user. For the fusion we assume two models: fusion of UWB and step-length with heading and fusion of UWB and step-length. The performance is evaluated on real data and it is shown that the UWB positioning error of 0.59 m is improved to 0.22 m and 0.36 m when fusion with both the step-length and heading or with only the step-length is used, respectively.

Dead reckoning

Sensor Fusion

10.1109/radioelektronika61599.2024.10524089

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Demonstration of space-time adaptive processing for DSI suppression in a passive radar

Václav Navrátil Andrew O’Brien J. Landon Garry Graeme E. Smith

Passive radar uses illuminators of opportunity instead of a dedicated radar transmitter. A number of already transmitted signals can be used, however, their nature is mostly continuous and their utilization is a complicated task. One of the key limiting factors of passive radar is the strong direct signal interference (DSI), even though many physical and signal processing countermeasures have already been developed. In the case of using terrestrial signals for airborne target detection, elimination of a certain elevation angle of arrival is a possible solution. As the real-world environment is non-stationary, adaptive methods are expected to give better results. The paper shows and compares two space-time adaptive vertical antenna array processing methods for DSI mitigation, applied in terrestrial navigation signal based radar. In addition, both methods are verified by processing signals captured under real-world conditions. Both methods offer more than 10 dB DSI suppression.

Space-Time Adaptive Processing

Passive Radar

Fire-control radar

SIGNAL (programming language)

Radar lock-on

Radar signal processing

Man-portable radar

10.23919/irs.2017.8008146

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Citations (7)

Concurrent Bidirectional TDoA Positioning in UWB Network With Free-Running Clocks

IEEE Transactions on Aerospace and Electronic Systems (2022)

Václav Navrátil Josef Krška F. Vejražka

This article proposes an approach of time-difference-of-arrival (TDoA) positioning in ultrawideband networks, where user tags localize themselves by means of the exploitation of the broadcasted synchronization messages of the anchor network. Such an approach promises an unlimited number of localized devices; moreover, the position is available directly at the user terminal. The key challenge of this method is to eliminate the errors caused by tag clock drifts, which render the TDoA measurements useless when left uncorrected. Our method employs extended Kalman filtering for the estimation of position and the elimination of the drift-induced errors. It is shown that the system performance is similar to that of the more common TDoA method, where the tags transmit blinks received by the anchors. However, the anchors are still able to receive the blink messages and estimate the position of those tags, since the synchronization messages are exploited. Therefore, it is possible to use both the directions of TDoA positioning concurrently; a limited number of tags is tracked by the infrastructure and all tags may compute their positions. The TDoA solutions have achieved a root-mean-square horizontal accuracy of 25.9 and 33.6 cm, respectively.

Position (finance)

FDOA

10.1109/taes.2022.3161895

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Citations (18)

Analysis and Measurement of IM3 Anomalies in Single- and Double-Band Low-Noise Amplifiers

Josef Dobec Jan Míchal Václav Navrátil Zdeněk Kolka

In the paper, a theoretical background of the unexpected third-order intermodulation power decrease at some levels of input power is discussed first. This anomaly can be partially explained by various physical phenomena, RF stress, e.g., as shown in the state-of-the-art review in the paper. Then a simulation of the IM3 dependency is performed, including a comparison between the computed and measured IP3 points. Finally the single- and double-band low-noise amplifiers designed by multi-objective optimization are measured from this point of view, and a frequency dependence of the IM3 anomalies is demonstrated. An improved optimization method is defined too.

Anomaly (physics)

10.1109/rfm50841.2020.9344764

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Pseudorange-Based IR-UWB Localization

Proceedings of the Satellite Division's International Technical Meeting (Online)/Proceedings of the Satellite Division's International Technical Meeting (CD-ROM) (2023)

Václav Navrátil Josef Krška

The application of the impulse-radio ultra-wide band technology is already established in indoor localization. Usually, two-way ranging (TWR) or time-difference of arrival (TDoA) approaches are utilized. In this paper it is shown that it is possible to perform time of arrival (ToA) positioning with accuracy similar to the TDoA. The ToA method estimates the bias between the clocks of the anchors (fixed infrastructure nodes) and the tag (localized user equipment). As a direct consequence, any timestamps taken by the tag may be converted to the common system timescale with accuracy of several nanoseconds. The approach is verified by real measurements. We demonstrate that the positioning solution can be obtained by least-squares optimization on epoch-by-epoch basis. We also show that the extended Kalman filter can be used to estimate tag position along with the bias and drift of its clock.

Pseudorange

Time of arrival

Ranging

Epoch (astronomy)

Angle of arrival

Position (finance)

10.33012/2023.19203

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Electronic Textbook of Electromagnetic Waves

D. Cernohorsky T. Urbanec V. Michalek S. Gona Václav Navrátil

Teaching university courses, which deal with the phenomena of the electromagnetic (EM) substantiality and their applications, is rather difficult due to their abstract nature. Therefore, teaching has to be accompanied by clear explanations and by simulations illustrating the exa- mined topics. This is why an electronic textbook (ET) of EM waves and applications was developed. The ET presents theoretical descriptions of selected EM phenomena on two levels - on a bachelor's one and a mas- ter's one. Descriptive parts of the ET are completed by computer programs, which enable the reader to simulate the studied phenomena. Moreover, the ET explains the practical implementation of simulation routines in MAT- LAB, which helps students to understand a relationship between rather complicated mathematics and a relatively simple source code of its software implementation. Since the ET is freely accessible on the web, students can use it whenever as a classical textbook, a handbook or a software package. This fact positively influences the stu- dents' knowledge and understanding as proven by our ex- perience.

Bachelor

Code (set theory)

Source

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Utilization of terrestrial navigation signals for passive radar

2022 IEEE Radar Conference (RadarConf22) (2017)

Václav Navrátil J. Landon Garry Andrew O’Brien Graeme E. Smith

Passive radars use transmissions from signals of opportunity in order to locate targets. The absence of a dedicated transmitter reduce the cost, complexity and detectability of the radar as compared to active radar systems. This paper investigates - for the first time - the use of signals of a metropolitan-wide terrestrial positioning system for passive radar. We present simple theoretical analysis predicts the efficacy of these terrestrial navigation signals for this application. Additionally, we demonstrate that aircraft can be observed in a passive radar system exploiting a terrestrial positioning transmission at 10 km bistatic range.

Passive Radar

Radar lock-on

Man-portable radar

3D radar

Fire-control radar

10.1109/radar.2017.7944317

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Citations (5)

Algoritmy určování polohy a fúze dat pro radionavigační systémy

Václav Navrátil

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Utilization of Carrier-Frequency Offset Measurements in UWB TDoA Positioning with Receiving Tag

Sensors (2023)

Josef Krška Václav Navrátil

High-capacity impulse-radio ultra-wideband (IR-UWB) indoor localization systems are typically based on the time difference of arrival (TDoA) principle. When the fixed and synchronized localization infrastructure, the anchors, transmit precisely timestamped messages, a virtually unlimited number of user receivers (tags) are able to estimate their position based on differences in the time of arrival of those messages. However, the drift of the tag clock causes systematic errors at a sufficiently high magnitude to effectively deny the positioning, if left uncorrected. Previously, the extended Kalman filter (EKF) has been used to track and compensate for the clock drift. In this article, the utilization of a carrier frequency offset (CFO) measurement for suppressing the clock-drift related error in anchor-to-tag positioning is presented and compared to the filtered solution. The CFO is readily available in the coherent UWB transceivers, such as Decawave DW1000. It is inherently related to the clock drift, since both carrier and timestamping frequencies are derived from the identical reference oscillator. The experimental evaluation shows that the CFO-aided solution performs worse than the EKF-based solution in terms of accuracy. Nonetheless, with CFO-aiding it is possible to obtain a solution based on measurements from a single epoch, which is favorable especially for power-constrained applications.

Carrier frequency offset

Time of arrival

Transceiver

10.3390/s23052595

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Citations (10)

Exploiting Terrestrial Positioning Signals to Enable a Low-Cost Passive Radar

IEEE Transactions on Aerospace and Electronic Systems (2018)

Václav Navrátil J. Landon Garry Andrew O’Brien Graeme E. Smith

This paper presents results from experiments that utilize Global-Positioning-System-like terrestrial positioning signals in a passive radar system to track aircraft over a metropolitan area. Unlike communication signals, these positioning signals offer unique properties that are advantageous for a passive radar. Exploitation of these properties provides an opportunity to reduce hardware complexity and to enable passive radar systems with a lower cost. This paper provides a detailed description of the signal processing in the context of low-cost hardware.

Man-portable radar

Passive Radar

Fire-control radar

Radar lock-on

3D radar

10.1109/taes.2018.2812458

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Citations (4)