Artikel and Buchkapitel
|||Indoor Positioning via Artificial Magnetic Fields , In IEEE Transactions on Instrumentation and Measurement, 2021. [bib] [abstract]|
Indoor positioning approaches are often based on electromagnetic wave signals with high frequency. However, signal reflections and the corresponding signal superpositions are challenging. As a result, there is still no indoor positioning technology established in commercial products, like smartphones or smartwatches. Recent publications have shown that this indoor positioning problem can be addressed by using artificial magnetic fields. However, the cubic attenuation of the magnetic field challenges technical implementations and limits the ranges. In this work, we propose an approachstriving to address these issues of magnetic indoor positioning via a simple electro-mechanical single-anchor concept in combination with a small wearable sensor circuitry. The terrestrial magnetic field together with amplitude and phase measurements resolve the position and the orientation of the tag. The proposed indoor positioning approach via artificial magnetic fields is tested in a corridor for a spacial region of approximately $100 m^2$. The mean positioning error in this experiment was calculated to be (1.0+-0.81)m$. The proposed indoor positioning approach via artificial magnetic fields and the corresponding measurement system can therefore be useful alternatives when considering applications in which simple implementation is more important than positioning precision.
|||Underwater Ultrasonic Multipath Diffraction Model for Short Range Communication and Sensing Applications , In IEEE Sensors Journal, volume 21, 2021. [bib] [pdf] [abstract]|
In acoustic underwater communication and sonar applications, obstacles inside and outside the line-of-sight (LOS) affect signal propagation. Both reflection and diffraction occur in underwater communication and measurement systems due to these obstacles. To the best of our knowledge, the influence of diffraction and reflection is neither described nor modeled for finite pulses yet. We propose and develop a multipath propagation model for spectral diffraction components and phase information of the received signal based on knife-edge diffraction together with reflections, transmission effects, and backscatter. This paper designs a short range underwater ultrasonic experimental system composed of an ultrasonic transceiver with wideband pulses and advanced spectral signal processing. We evaluate our proposed model with measurements made in a water tank with an obstacle moved between the transmitter and receiver. When the model includes all major propagation components and effects, it achieves an accuracy for localization of 97% of the results in the range of twice the obstacle diameter in our test setup.
|||MAMPI-UWB—Multipath-Assisted Device-Free Localization with Magnitude and Phase Information with UWB Transceivers , In Sensors Multidisciplinary Digital Publishing Institute, volume 20, 2020. [bib] [abstract]|
In this paper, we propose a multipath-assisted device-free localization (DFL) system that includes magnitude and phase information (MAMPI). The DFL system employs ultra-wideband (UWB) channel impulse response (CIR) measurements, enabling the extraction of several multipath components (MPCs) and thereby benefits from multipath propagation. We propose a radio propagation model that calculates the effect on the received signal based on the position of a person within a target area. Additionally, we propose a validated error model for the measurements and explain the creation of different feature vectors and extraction of the MPCs from Decawave DW1000 CIR measurements. We evaluate the system via simulations of the position error probability and a measurement setup in an indoor scenario. We compare the performance of MAMPI to a conventional DFL system based on four sensor nodes that measures radio signal strength values. The combination of the magnitude and phase differences for the feature vectors results in a position error probability that is comparable to a conventional system but requires only two sensor nodes.
|||A new localization algorithm based on neural networks , In Proceedings of the 3rd KuVS/GI Expert Talk on Localization, 2018. [bib] [pdf] [abstract]|
Indoor localization plays a major role in a wide range of applications. To determine the location of a tag, localization algorithm is required. In the past, machine learning algorithms were difficult to implement in consumer hardware, but with the advent of tensor processing units, even smartphones are capable to use artificial intelligence to solve complex problems. In this paper, we investigate a machine learning algorithm based on neural networks and compare the result to a linear least squares estimator. We design and evaluate different neural networks. Based on our observation, the neural network delivers poor performance compared to the linear least squares estimator.
|||UWB-based Single Reference Point Positioning System , In ITG-Fachbericht-Mobilkommunikation VDE VERLAG GmbH, 2017. [bib] [abstract]|
Indoor positioning enables new applications, for instance monitoring of goods in smart factories. For such applications, indoor positioning requires cost-effective solutions with high accuracy. State-of-the-art positioning systems are expensive due to high infrastructure and maintenance costs. In this paper we suggest an accurate UWB-based single reference point positioning system using multiple antennas. We compare lateration and hyperbolic lateration as positioning methods and present efficient algorithms for UWB-based single reference point positioning systems. We present theoretical limits based on the Cramer-Rao lower bound and derive an error estimation as well as evaluation results. Our measurements indicate that decimeter accuracy is possible.
|||Survey of challenges and towards a unified architecture for location systems , In Journal of Network and Computer Applications, volume 67, 2016. [bib] [pdf] [abstract]|
Abstract Localization is a key aspect of emergent applications in the medical, industrial and consumer field. In this article we survey state of the art, identify current challenges and issues for localization systems and suggest a unified layered architecture. The analysis reveals that challenges cannot be addressed in an isolated manner for example, energy consumption is tied to the choice of algorithm and employed hardware. To separate various challenges and investigate them independently, we propose the concept of position providers. Position providers in the lower layers allow abstraction of positioning methods, positioning algorithms and positioning hardware. Thereby, a position provider encapsulates methods, algorithms and hardware. Furthermore, we suggest a classification of position providers inspired by related work. We propose a unified architecture for location systems which uses positioning and integration layers as main building blocks.
|||Iterative approach for anchor configuration of positioning systems , In ICT Express, volume 2, 2016. [bib] [pdf] [abstract]|
With anchor positions and measurements of distances between an object and anchors, positioning algorithms calculate the position of an object, e.g. via lateration. Positioning systems require calibration and configuration prior to operation. In the past, approaches employed reference nodes with GPS or other reference location systems to determine anchor positions. In this article, we propose an approach to determine anchor positions without prior knowledge. We evaluate our approach with simulations and real data based on the Decawave DW1000 radio and show that the error is proportional to the mean error of the distance estimation.
|||Höhenbestimmung mittels Luftdrucksensoren und differentieller Messung für Indoor-Anwendungen , In ImpulsE, volume 17, 2013. [bib]|
|||High Precision Open Laboratory 3D Positioning System for Automated Underwater Measurements , In Global Oceans 2021: San Diego - Porto, 2021. [bib] [pdf] [abstract]|
Underwater measurements in a lab environment are challenging, with sensors or objects that need to be positioned precisely and reproducible. Existing systems are expensive, often not suited for underwater usage, and not flexible. Underwater's main challenges are determining the "exact" relative position and a positioning system that is operated reliably in a wet environment. The commercial systems available are fixed in dimensions and cannot be fitted to lab conditions. We present our open solution, which is scalable and flexible to be adapted to other applications. The solution consists of a table with readily adaptable components such as positioning components integrated into an MQTT environment with precise stepper motor units. The table is easy to adapt in size, and we take care of special placement for electrical components to not get into contact with water. The system achieves a noticeable performance and is fully automated. The speed is adaptable between 1mm/s and 30mm/s, with a resolution of 0.1mm.
|||Flexible Arbitrary Signal Generation and Acquisition System for Compact Underwater Measurement Systems and Data Fusion , In Global Oceans 2021: San Diego - Porto, 2021. [bib] [pdf] [abstract]|
For the implementation of compact underwater measurement systems, much time is spent integrating various sensor and processing components and their control and synchronization. Especially for multi-sensor applications, proprietary solutions do not scale easily and are not designed for use in a distributed measurement system. We propose a well-established protocol Message Queuing Telemetry Transport (MQTT) for integration of sensors with a broker as a central data hub as a key system component. We implemented a flexible, distributed multi-sensor measurement system, by using open-source libraries. The multi-sensor system was successfully tested and operated with five underwater sensor devices and user data rates up to 2.73 MB/s.
|||Comparison of I/Q- and Magnitude-based UWB Channel Impulse Responses for Device-free Localization , In International Conference on Localization and GNSS, 2021. [bib] [abstract]|
Ultra-wideband (UWB) channel impulse response (CIR) measurements contain information about the presence and location of a person in proximity of sensors. Typically, parts of the CIR, such as the amplitudes of specific multipath components (MPCs) or the magnitudes of the complete CIR are employed for localization. Discarding the phase information of the CIR measurements ignores important information and finally requires longer CIR measurements. Especially in setups where only a small number of sensors are deployed, discarding information degrades the system performance. In this paper, we propose a method that processes the I/Q values of CIR measurements, by aligning, cropping, and rotating the measured CIRs. Localization with I/Q-based CIR measurements is compared with results of magnitude-based approach. In summary, I/Q-based CIR measurements reduce localization errors by approx. 10%. Finally, I/Q-based CIRs provide comparable results with CIRs that are 30% shorter compared to magnitude-based solutions.
|||Differential Ultrasonic Detection of Small Objects for Underwater Applications , In Global Oceans 2020: Singapore – U.S. Gulf Coast, 2020. [bib] [pdf] [abstract]|
Exploration of natural and artificial underwater structures is an actual field in development and research projects. Acoustic detection methods are well known and can be used to create seabed and subbottom profiles. The systems have limitations for detection of small objects, especially in presence of large acoustic reflectors. The detection of flat buried objects like unexploded ordnance (UXO) is very difficult with acoustic systems. This work presents a simple setup that utilizes three unfocused transceivers to detect small acoustic disturbances in presence of large acoustic reflectors. We suggest a differential ultrasonic receiver to eliminate equal signal components of two overlapping receivers to detect small objects. Furthermore, we present a differential single-receiver system and an evaluation of different algorithms for data visualization and compare with the frequently applied envelope in single receiver systems. It is possible to detect small objects with the diameter of $6 unitmm$ located in the water-sediment interface with the differential receiver setup.
|||MAMPI – Multipath-assisted Device-free Localization with Magnitude and Phase Information , In International Conference on Localization and GNSS, 2020. [bib] [abstract]|
Narrowband radio-frequency (RF)-based device-free localization (DFL) systems suffer from multipath propagation. Therefore, we propose multipath-assisted device-free localization with magnitude and phase information (MAMPI), a DFL system that employs ultra-wideband (UWB) channel impulse response (CIR) measurements between a transmitter and receiver and thereby benefits from multipath propagation. We implement a model that includes raytracing, diffraction, and inaccuracies of measurements in a validated error model. The multipath-assisted DFL system creates feature vectors at any position based on magnitude and phase measurements of each multipath component (MPC) of the CIR. We evaluate our new approach with a position error probability based on the propagation model including errors, as well as a distance metric of the feature vector of the positions. We compare the performance of the system with a line-of-sight solution with four instead of two nodes and variants of magnitude-only and phase-only approaches. By combining the magnitude and phase measurements of a multipath-assisted DFL system, we achieve a position error probability that is similar to the conventional DFL system.
|||Development of an Electro Impedance Tomography-based Platform for Measurement of burial Depth of Cables in Subsea Sediments , In Oceans 2019, 2019. [bib] [abstract]|
Cables buried in the seabed are objects of interests especially as companies have to verify that the buried depth of the cables is in the expected range, typically $1~m$. Although several measurement systems have been designed in the past, there is no solution available that provides an accuracy of $pm10~cm$ for this purpose. In our approach we suggest to model and measure the electrical field and electrical impedance to determine the depth of a sea cable. In the first step we develop an electrical static field model for analytic investigations. We validate the model by a simulation tool and provide results for critical environmental parameters that affect our measurement accuracy.
|||On the Effective Length of Channel Impulse Responses in UWB Single Anchor Localization , In International Conference on Localization and GNSS, 2019. [bib] [abstract]|
Recently, single anchor localization evolves as a new research topic that exploits multipath propagation for calculation of tag positions. With a combination of movement information and particle filters, they provide a precision that is similar to multi-anchor systems. However, a systematic approach to the design and implementation of such systems is not yet available. The combination of theory and mathematical modeling for channel impulse responses is still an open research question that we address in this paper. Therefore, we propose a new representation of a channel impulse response targeted for single anchor localization systems. Based on this representation, we model the relationship between tag positions and channel impulse responses and evaluate the statistic properties of channel impulse responses in this application. In this paper, we introduce a new metric for the assessment of anchor positions, the effective length of CIRs. By the shortest effective length of a set of CIRs, we identify the best anchor position, since it indicates the position where requirements for the measurement of the channel impulse response are lowest.
|||Minimizing Indoor Localization Errors for Non-Line-of-Sight Propagation , In International Conference on Localization and GNSS, 2018. [bib] [abstract]|
Indoor Localization becomes more important, as it provides additional context for many applications for example in the Internet of Things (IoT). Time-of-flight measurements, as a basis for distance estimation, are susceptible for non-line-of-sight (NLOS) propagation, resulting in large distance errors. Standard least squares solutions to estimate the targets location do not account for NLOS propagation which results in large scale errors. We investigate the difference between L1- and L2-minimization and present a new framework based on a modified RANSAC approach. Additionally, we investigate a Support Vector Machine (SVM) to detect NLOS measurements.We present simulation and measurement results and evaluate our approach. We show that our framework delivers better performance in presence of NLOS propagation compared to plain L1- or L2-minimization.
|||RF-Based Safety-Critical Hybrid Localization , In The Ninth International Conference on Indoor Positioning and Indoor Navigation (IPIN), 2018. [bib] [abstract]|
In safety-critical environments, e.g. paint or machine shops, precise knowledge of positions of persons is important. If an emergency is detected, e.g. a fire or an intruder in the safety-critical area of heavy machinery, emergency shutdown procedures are activated. This requires fine-grained localization with a tag-based localization system, where the person carries a tag. Without a person carrying a tag, precise localization and detection is difficult. In this paper, we propose a RF-based hybrid localization system for safety-critical localization that consists of two major components: a tag-based and device-free subsystem. The device-free subsystem provides coarse-grained localization and monitors a gate area, serving as an entrance towards the safety-critical area where fine-grained localization is required. We propose an architecture of the system, discuss our setup and evaluate typical use cases. Our preliminary evaluation demonstrates that our system detects the correct state of the hybrid localization system with an accuracy of 90%.
|||TriClock – Clock Synchronization compensating Drift, Offset and Propagation Delay , In IEEE International Conference on Communications, 2018. [bib] [abstract]|
In wireless sensor networks (WSN) precise clock synchronization is still a challenge e.g. for synchronized medium access control (MAC). State of the art solutions require many messages or neglect clock drifts or propagation delay. In multi-hop networks synchronization errors increase with the number of hops because numerous messages increase latency. The latency and clock drift reduces synchronization accuracy. Finally, propagation delay introduces additional synchronization offsets. We introduce a novel synchronization protocol that requires a single message to compensate both clock offset and clock drift and one additional message to account for propagation delay. With this minimal amount of messages, an efficient multi-hop synchronization is practicable. We implement our approach on a DWM1000 hardware and evaluate the protocol in single-hop and multi-hop configuration. In our preliminary experiments, we achieved a synchronization accuracy of 0.46 ns in a single-hop configuration within 3.6 ms and 6 ns in a multi-hop configuration for 5 hops within 11 ms which is appropriate for MAC and time-division multiple access (TDMA) implementations.
|||Sundew: Design and Evaluation of a Model-based Device-free Localization System , In The Ninth International Conference on Indoor Positioning and Indoor Navigation (IPIN), 2018. [bib] [abstract]|
The state-of-the-art in device-free localization systems based on RF-measurements is fingerprinting. Fingerprinting requires reference measurements called fingerprints that are recorded during a training phase. Especially in device-free localization systems, recording of reference measurements for fingerprinting is a tedious, costly, and error-prone task. In this paper, we propose Sundew, a model-based device-free localization system that does not need fingerprinting in the sense of reference measurements but is able to calculate signal strength values at any position and compare it to actual measurements after a simple calibration phase. Sundew — as any device-free localization system — requires a metric for comparison of feature vectors. In this paper, we investigate the influence of nine different distance metrics on the positioning accuracy. Simulations and measurements show that our suggested model-based device-free localization system works best with the L 1 distance metric. Sundew estimates 90% of positions in a 2.5m x 2.5m grid correctly, independent of the orientation of the person in the target area.
|||S-TDoA - Sequential Time Difference of Arrival - A Scalable and Synchronization Free Approach for Positioning , In IEEE Wireless Communications and Networking Conference, 2016. [bib] [abstract]|
In the past various solutions for localization evolved to productive usage for wireless applications. These solutions are robust, precise and energy efficient. However, scalability, complexity and flexibility are still open issues. Especially, supported number of objects or update rates for localization are still limiting factors for the usage of the systems. In this work we suggest an approach called S-TDoA which stands for sequential Time Difference of Arrival that supports unlimited number of objects and high update rates. The key concept is a sequential triggering of anchors that send periodic messages. Tags determine their position by listening to the anchor messages and measuring time intervals. Additionally, this approach enhances security because tags are not visible as they do not send messages. We implement and evaluate S-TDoA in a localization system based on UWB-RF- Chips. The preliminary results demonstrate the advantages of our implementation regarding scalability and update rates as well as privacy.
|||Impact of Altitude Difference for Local Positioning Systems and Compensation with Two-Stage Filters , In 2016 International Conference on Localization and GNSS, 2016. [bib] [abstract]|
In range-based positioning systems, an altitude difference between tag and reference plane causes errors in two- and three-dimensional positioning. We analyze how these errors reduce accuracy of Local Positioning Systems (LPS) and show how compensation of the altitude difference improves performance of positioning. In this paper, we consider the availability of additional altitude information and transform the three-dimensional positioning problem into a two-dimensional problem. We provide algorithms for time-based positioning systems with a two-stage estimator for Two-Way Ranging and Time Difference of Arrival and incorporate additional altitude information. We simulate our approach for altitude difference compensation and provide an evaluation based on a Ultra-Wideband (UWB) radio with ranging capability and a barometric sensor for additional altitude information. A comparison is then made between our approach and standard solutions such as the Extended Kalman filter and the Unscented Kalman filter. Finally, the successful decrease in the positioning error for two- and three-dimensional positioning system, using the system disclosed herein, is illustrated. Based on our analysis, we derive practical solutions to deal with altitude differences for positioning systems.
|||Introduction, Discussion and Evaluation of Recursive Bayesian Filters for Linear and Nonlinear Filtering Problems in Indoor Localization , In The Seventh International Conference on Indoor Positioning and Indoor Navigation, 2016. [bib] [abstract]|
Linear and nonlinear filtering for state estimation (e.g. position estimation or sensor fusion) for indoor positioning and navigation applications is a challenging task. Sensor fusion becomes more important with cost-effective sensors being readily available. However, state estimation with recursive Bayesian filters for sensor fusion and filtering are difficult to apply. We present an overview for the general Bayesian filter and derive the most commonly used recursive Bayesian filters, namely the Kalman, extended Kalman and the unscented Kalman filter along with the particle filter. The later Kalman filters are extension of the original Kalman filter, which are able to solve nonlinear filtering problems. The particle filter is also able to solve nonlinear filtering problems. We evaluate the recursive Bayesian filters for linear and nonlinear filtering problems for sensor fusion from relative dead reckoning positioning data and absolute positioning data from an UWB positioning system. We discuss and evaluate performance and computational complexity and provide recommendations for the use case of the recursive Bayesian filters.
|||QRPos: Indoor Positioning System for Self-Balancing Robots based on QR Codes , In The Seventh International Conference on Indoor Positioning and Indoor Navigation, 2016. [bib]|
|||Investigation of Anomaly-based Passive Localization with Received Signal Strength for IEEE 802.15.4 , In The Seventh International Conference on Indoor Positioning and Indoor Navigation, 2016. [bib] [abstract]|
Localization has important applications, for instance intrusion detection and elderly care. Such applications benefit from Device-free passive (DfP) localization systems, which employ received signal strength measurements (RSSM) to detect and track entities that neither participate actively in the localization process nor emit signals actively. RSSMs include received signal strength indicator (RSSI), energy detection (ED) and link quality indicator (LQI) measurements. This paper compares different packet-based RSSMs for DfP localization and presents detection results of a DfP anomaly-based detection system employed by IEEE 802.15.4 compliant devices. Furthermore, we investigate techniques for anomaly detection with continuous RSSI measurements.
|||Indoor Localization based on Bi-Phase Measurements for Wireless Sensor Networks , In 2015 IEEE Wireless Communications and Networking Conference (WCNC): - Track 3: Mobile and Wireless Networks (IEEE WCNC 2015 - Track 3- Mobile and Wireless Networks), 2015. [bib] [abstract]|
Indoor localization is important for medical and industrial application as well as for wireless emergency and security systems. For such applications an accuracy within a few meters is desired. Available radio based systems within that accuracy are neither cost effective nor easy to deploy. In this work, we suggest an approach called biphase measurement based on phase measurements with two frequencies to determine the location of a tag. We design and build a complete indoor positioning system based on bi-phase measurements with easy to deploy wireless sensor nodes. The wireless sensor nodes shape anchors and tags and communicate results to a location engine of the indoor positioning system. Our implementation comprises lowcost IEEE802.15.4 radio chips with built-in support for phase measurements unit for both, anchor and tags. We compute the position of the tag based on distance estimation retrieved with bi-phase measurements. We evaluate our indoor positioning system providing first measurement results for accuracy and precision and discuss trade-off between scalability, real-time and accuracy.
|||Wireless Medical Sensors - Context, Robustness and Safety , In 49th annual conference of the German Society for Biomedical Engineering (BMT 2015), 2015. [bib]|
|||Accurate Radio Distance Estimation by Phase Measurements with Multiple Frequencies , In The Fifth International Conference on Indoor Positioning and Indoor Navigation 2014 (IPIN 2014), 2014. [bib] [abstract]|
Indoor localization is beneficial for logistics, industrial applications and for several consumer applications. In the area of logistics, e.g. warehouses, localization accuracy within a few meters is desired. Available radio based systems within that accuracy are neither cost effective nor easy to deploy. Distance estimations are one possible method for localization. In this work, we propose phase measurements between two wireless sensor nodes for distance estimation. We introduce a mathematical model to estimate distances from phase measurements with multiple frequencies and provide a systematic analysis of possible sources of errors. Additionally, we derive requirements, e.g. resolution and speed for a phase measurement unit to reach certain accuracy. To proof our theoretical results, we present evaluation results based on our implementation. Our implementation comprises a low cost IEEE 802.15.4 hardware with a built-in phase measurement unit. We implement the developed algorithm for distance estimation in our wireless sensor network and use two wireless sensor nodes to perform a phase measurement. The contribution of the paper comprises a new model for phase measurements to estimate distances and a preliminary evaluation with our hardware.
|||Experimental Evaluation & Optimization of a UWB Localization System for Medical Applications , In 48th annual conference of the German Society for Biomedical Engineering (BMT 2014), 2014. [bib]|
|||Evaluation of Radio Based, Optical and Barometric Localization for Indoor Altitude Estimation in Medical Applications , In The Fifth International Conference on Indoor Positioning and Indoor Navigation, 2014. [bib] [abstract]|
The advances of electronics provide options for improved monitoring of patients in clinical environment.Medical applications like blood pressure monitoring require precise and wireless altitude measurement in indoor environment. An error of only a few centimeters may lead to mistreatment of patients.Furthermore, user requirements like small form factor, usability and robust operation are important in the medical field.Existing evaluations of indoor localization systems focus on accuracy analysis of x- and y-coordinates and not on the z-coordinate (altitude). In this paper, we define evaluation criteria for altitude estimation in medical applications. We compare an Ultra-Wide-Band indoor localization system, an optical Microsoft Kinect camera system and our own development of a wireless barometric sensor against these criteria. We present a comparative measurement setup, results and a final evaluation of the three systems in an indoor environment.
|||Precise Indoor Altitude Estimation based on differential barometric Sensing for wireless Medical Applications , In Body Sensor Networks Conference 2013 (BSN2013), 2013. [bib] [abstract]|
Some medical applications require precise information of position and orientation of a patient as changes affect pressure condition inside the body. In this paper we focus on altitude estimation, where altitude is a distance, in vertical direction, between a reference and a point of a human body. We suggest equipping wireless sensor nodes with high resolution pressuresensors to calculate the altitude with the barometric formula. We implement a body sensor network based on IEEE 802.15.4 and synchronization mechanism with a reference. Pressure variations due to environmental effects are compensated by cancellation with this differential measurement setup. We demonstrate the need for differential measurements and show with a series of measurements that environmental pressure variations have no significant effect on the proposed altitude estimation. Compared to existing systems, our solution is cost effective, easy to deploy and provides a flexible tradeoff between precision and location lag by adjusting a filter constant.
|||Modeling the Magnitude and Phase of Multipath UWB Signals for the Use in Passive Localization , In 16th Workshop on Positioning, Navigation and Communication, 2019. [bib] [abstract]|
Radio-frequency (RF)-based device-free localization (DFL) systems measure RF parameters such as the received signal strength or channel state information to detect and track objects within a certain area. However, the change of the RF signal caused by the object is superimposed with various changes of the RF signal due to multipath propagation, especially in indoor environments. In this paper, we develop a model for ultra-wideband (UWB) channel impulse response (CIR) measurements for application in DFL systems. The model predicts received signal parameters in a setup with a transmitter and a receiver node, a person and multipath propagation. Different from other approaches, the RF hardware, and the model provides both magnitude and phase information for individual multipath components. We evaluate the new model with real measurements that have been conducted with a Decawave DW1000 radio chip. For the magnitudes, we achieved a correlation factor from 0.78 to 0.87 and maximum mean and standard deviation errors of 1.7 dB and 2.2 dB respectively. For the phase, we achieved correlation factor from 0.6 to 0.81 and maximum mean and standard deviation errors of 0.32 dB and 0.47 dB respectively, showing that the prediction of our proposed model for the magnitude and phase fits well to our measurements.
|||Evaluation of time-based ranging methods: Does the choice matter? , In 14th Workshop on Positioning, Navigation and Communication, 2017. [bib] [abstract]|
Positioning is useful in a number of applications, for instance smart home, smart factory and health care applications. Time-based ranging methods for positioning are the state-of-the-art but require precise timestamping. Sophisticated ranging methods compensate sources of errors, for instance clock drift caused by a crystal or an asymmetrical measuring principle, to provide precise timestamping. So far, no comprehensive study of different time-based ranging methods using the same hardware and the same evaluation setup was carried out. Consequently, we discuss, implement and evaluate five time-based ranging methods, including Two-Way Ranging, Double Two-Way Ranging, Asymmetrical Double-Sided Two-Way Ranging, Symmetrical Double-Sided Two-Way Ranging and Burst Mode Symmetric Double-Sided Two-Way Ranging. We evaluate accuracy, precision, robustness and run time for the ranging methods and answer the question if the choice of the time-based ranging method matters.
|||Weighted Online Calibration for Odometry of Mobile Robots , In IEEE ICC Workshop on Advances in Network Localization and Navigation (ANLN), 2017. [bib]|
|||Anomaly-based Device-free Localization with Particle Filtering , In Workshop on Dependable Wireless Communications and Localization for the IoT, 2017. [bib] [abstract]|
In the Internet of Things (IoT), devices, e.g. sensors or actuators, transmit packets to transfer data. For the IoT localization information is crucial, as it provides additional context for the data. We envision that devices in the IoT know their position and on receipt of a packet, the received signal strength is measured. This measurement is used to build a device-free localization (DFL) system to improve the dependability of the IoT system. DFL systems are able to detect and track persons within a target area that neither wear a device nor participate actively in the process of localization. This work presents an anomaly-based DFL system that measures if a person affects the radio frequency (RF) propagation and determines the position with a particle filter. In our 65m 2 indoor testbed, we employ eight IEEE 802.15.4 compliant wireless transceivers and estimate the position of a person with a median localization error of 1.4m.
|||Modeling Received Signal Strength and Multipath Propagation Effects of Moving Persons , In 14th Workshop on Positioning, Navigation and Communication, 2017. [bib] [abstract]|
Device-free localization (DFL) systems detect and track persons without devices that participate in the localization process. A person moving within a target area affects the electromagnetic field that is measured by received signal strength (RSS) values. Consequently for DFL systems modeling of RSS is important and still an open issue. In this paper, we develop a simple model for prediction of RSS values in a setup with transmitter and receiver devices, a person and multipath propagation. We design and implement the model as a superposition of both, knife-edge diffraction to account for the change made by the person, and, propagation effects such as multipath propagation that result in reflection and path loss including the antenna characteristics. We evaluate our model in comparison with real measurements in various setups with and without multipath propagation. We achieve an accuracy that is close to our hardware limitations, which is the resolution of the measured RSS values of the receiver.
|||Comparison of wired and wireless synchronization with clock drift compensation suited for U-TDoA localization , In 13th Workshop on Positioning, Navigation and Communication, 2016. [bib] [abstract]|
Indoor localization with Uplink Time Difference of Arrival (U-TDoA) provides good scalability, high updates rates and high accuracy. However, clock errors lead to localization errors and synchronization is important. In this paper, we design and implement wired and wireless synchronization and provide a comparison between them. We design and implement a wireless synchronization with clock drift compensation. For wired and wireless synchronization, we discuss reasons for clock deviation that lead to localization errors. We evaluate both approaches in a U-TDoA measurement setup. Finally, we provide recommendations for wired and wireless synchronization.
|||Mobile Robot Seamless Localization with Localization Optimized QR Codes , In 12th Workshop on Positioning, Navigation and Communication, 2015. [bib] [abstract]|
Indoor navigation is a prerequisite for new emerging applications for autonomous mobile robots. Additionally to the location of a robot, the orientation is important for these applications. Furthermore, a solution to this localization problem should be inexpensive and easy extensible for new areas of a building. We propose inexpensive optical landmarks based on localization optimized Quick Response (QR) code for localization of the landmark within an image to reduce computational cost. We further specify the error correction level, border, and size of the QR code for optimal localization. The proposed QR code combines GPS coordinates and local coordinates which allows seamless integration of our approach. We perform image processing to estimate the distance and orientation of a mobile robot with respect to the localization optimized QR code. To evaluate our approach we implemented the approach in an Android application and measured the performance in experiments. Additionally, we suggest a method to retrieve more accurate GPS information based on the measured orientation and distances. Our implementation achieves update rates of up to 3 Hz and an accuracy of 1 cm
|||Modeling UWB Multipath Propagation considering Material-Dependent Reflection Effects , Technical report, Technische Hochschule Lübeck (Center of Excellence CoSA, ed.), 2021. [bib] [pdf] [abstract]|
In Industry 4.0, indoor localization evolves as animportant research area. Ultra-Wide-Band (UWB) transceiversystems allow single-anchor based tag localization. The short tem-poral extent of UWB signal impulses enables the interpretationof multi-propagation paths. Accordingly, the anchor capturesthe Channel Impulse Response (CIR) of superposed signalechoes from all existing paths. Reconstruction of superposingeffects at the receiver antenna requires the prediction of eachpath’s received signal power. So far, prediction models considerpropagation losses. In the case of reflections, the losses of UWBsignals are not well documented. Therefore, we introduce a newtransceiver model considering multipath and material-dependingreflection losses. Based on our measurements, we show thematerial-dependency of reflection losses and quantify them byrefraction indices as we introduce them in our model.
|||Modeling the Path Losses of Ultra-Wideband Signals in Multipath Propagation Channels , Technical report, Technische Hochschule Lübeck (Center of Excellence CoSA, ed.), 2021. [bib] [pdf] [abstract]|
Recently, a single anchor localization system is a new scientific approach for localization of a tag in a given room by utilizing only one anchor. For this new localization approach, a model for the impulse response is necessary that includes multipath propagation. Theoretically, each position has a unique signal response to a transmitter in a given room, which is called a fingerprint. A part of this fingerprint is the path losses of the original signal and the signal echo. The calculation of the distance between transmitter and receiver, based on a receiving signal, is a basic approach. However, this paper determines the path loss coefficient in a given room to obtain an approximate model that describes the path loss. The evaluation measurement shows a model accuracy of d1 = 11 cm. In sum, this model is a good approximation, which needs further researching to improve the model.
|||Object Localization in Seawater via Electrical Impedance Measurements , Technical report, Technische Hochschule Lübeck (Center of Excellence CoSA, ed.), 2021. [bib] [pdf] [abstract]|
Artificial technical infrastructures already exist on and in the seabed, including cables for energy and data communication and pipelines for oil and gas. There are also contaminated sites such as blind munitions, which can contaminate the sea and which can hinder the development of new infrastructures. Objects such as blind ammunition, mines and barrels should be discovered and removed in order to avoid damage to people and the environment. Deep-sea cables and pipelines are regularly checked for their laying depth, for example, which can change due to currents. One approach to the tracking of cables, the detection and localization of metal objects is electrical impedance spectroscopy and tomography. The first results of this approach are presented here, which were achieved with a test stand in which impedance measurements in salt water are reproducible under laboratory conditions. With the test stand variable objects can be varied in their position in space in relation to a static electrode array. The results show the horizontal and vertical sensitivity of an electrode array for different dimensions of objects, based on the measured impedance. A simple algorithm that uses previously measured impedances in the form of a lookup table basically shows the successful detection and localization of objects in the vicinity of the array.
|||Modeling the Interference of Ultra-Wideband Signals in Multipath Propagation Channels , Technical report, Technische Hochschule Lübeck (Center of Excellence CoSA, ed.), 2021. [bib] [pdf] [abstract]|
Recently, one anchor Ultra-Wideband localization systems evolve as a new approach to determine the position of a tag with minimum infrastructure effort. The key of this method is to use a model of the propagation channel including the behaviour of multipath propagation. An issue of multipath propagation channels is, that signal echos can interfere at the receiver. To get a good model of the channel it is necessary to consider interference behaviour correctly. In this paper, we propose a model for Ultra-Wideband signals in multipath propagation channels that consider the phenomenon of interference and evaluate the model with measurements. We show that the proposed model is not able to represent a received signal in amplitude and signal shape completely correct. Additionally, we used the energy of a signal to compare the model and the measurement. We show that the changing of the energy due to different interference patters is represented by the model in a good agreement with the measurements.
|||Gigahertz Ground Penetrating Radar (GPR) for Sediment Exploration , Technical report, Technische Hochschule Lübeck (Center of Excellence CoSA, ed.), 2021. [bib] [pdf] [abstract]|
In order to detect measurement objects (e.g. cables and ammunition) in the Wadden Sea, a procedure via ground penetrating radar from a drone is to be determined. For this purpose, a feasibility study with different dispersion media will be carried out in an aquarium. First, a series of measurements in water with a high degree of absorption will be implemented, followed by air as reference medium, followed by sediment with different degrees of saturation with seawater. The measured data are then evaluated in order to determine the attenuation and the propagation velocity for each medium. The aim is to determine the attenuation to determine the required signal power for GPR with GHz in the Wadden Sea with penetration depth up to two meters lateron.
|||Understanding and Prediction of Ultra-Wide Band Channel Impulse Response Measurements , Technical report, Technische Universität Braunschweig, 2019. [bib] [pdf] [abstract]|
Recently, ultra-wide band transceiver systems have provided data transfer, timestamps and channel impulse response measurements to the user. The interpretation of the timestamps and the channel impulse response, however, is difficult and not intuitive. In simple scenarios, line of sight and non-line of sight pulses can be distinguished easily, which simplifies the reconstruction. For more complex scenarios, the interpretation remains difficult and is still an unsolved problem. In this paper, we investigate the channel impulse response measurements of the DecaWave DW1000 ultra-wide band transceiver and model the expected results for simple scenarios based on information provided from the transceiver data sheet. We will show that we are able to predict the measurement results of the transceiver with acceptable accuracy by applying the model above in experiments.
|||A Practical Toolbox for Getting Started with mmWave FMCW Radar Sensors , Technical report, Technische Universität Braunschweig, 2019. [bib] [pdf] [abstract]|
In this paper, we sum up our experience gathered working with mmWave FMCW radar sensors for localization problems. We give a glimpse of the foundations of radar that is necessary to understand the benefit and advantages of this technology. Moreover, we introduce our open-source software toolbox pymmw based on Python for Texas Instruments IWR1443 ES2.0 EVM sensors to provide students and researchers easy access to those radar sensors. In doing so, one can jump right into sensing with mmWave FMCW radar from a practical point of view and start doing experiments and developing own applications. Finally, pymmw is used for data acquisition of a scene illuminated by three virtual radars in three different states of occupancy showing the potential of mmWave FMCW radar for indoor and distance-based localization applications.
|||Impact of the antenna orientation for distance estimation , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf] [abstract]|
Indoor localization is important for a wide range of use cases including industrial, medical and scientific applications. The location accuracy is affected by the localization algorithm and the quality of the measurements as input for the algorithm. Many indoor localization systems employ ultra-wideband distance measurements, as they offer high accuracy and are cost effective. One of the methods for distance measurement is twoway ranging. This paper investigates the impact of the antenna orientation on the distance measurement based on symmetrical double-sided two-way ranging. We show that up to 0.25m of the measurement error is attributed to the orientation of the antennas. We provide explanations and suggest solutions to reduce the effect.
|||Lessons learned: Indoor Ultra-Wideband localization systems for an industrial IoT application , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf] [abstract]|
Since ultra-wideband (UWB) transceivers are available for wireless sensor networks, the usage in research and industry increased. Research efforts resulted in methods, measurement results, and solutions under laboratory conditions for a variety of indoor localization problems provided to the community. In this paper, we present an indoor positioning system (IPS) that is installed in a $mathbf1500 m^2$ real world production facility. In this real-world application, we faced some challenges that research has not addressed yet. For instance, challenges are receiving UWB signals from other floors in a multistory building through windows and multipath effects at walls like reflexions. We present solutions to increase the availability of such large-scale IPS, give a performance evaluation and recommendation for a modified NMEA sentence named iNMEA for IPS receivers.
|||Comparison of Antenna Types and Frequency Bands for Radio-based Device-free Localization , Technical report, Technische Universität Braunschweig, 2018. [bib] [pdf] [abstract]|
Radio-based device-free localization systems measure effects on radio signals e.g. signal strength variations to locate objects or persons in a target area. Such systems detect and track persons that do not participate in the localization process. Models for calculating the radio signal propagation are key for the performance in device-free localization systems. Received signal strength (RSS) is simple to measure. However, it is susceptible to changes in the environment and multipath propagation. In this paper, we compare PCB antennas to a circularly polarized cloverleaf antenna and measurements in the 2.4 GHz with measurements to the 868MHz ISM band. We investigate especially if a circularly polarized cloverleaf antenna is resilient against multipath propagation. Our preliminary results demonstrate that our model is suitable to the 868MHz band and the use of the 868MHz band increases the area where a person affects the RSS. The use of a circularly polarized cloverleaf antenna does not help to avoid multipath propagation.
|||Evaluation of Bluetooth Positioning for Medical Device Tracking , GRIN (T. M. Buzug et. al., ed.), 2017. [bib]|
|||Investigation of Anomaly-based Passive Localization with IEEE 802.15.4 , Technical report, RWTH Aachen University, 2016. [bib] [pdf]|
|||Position Calculation with Least Squares based on Distance Measurements , Technical report, Fachhochschule Lübeck, 2015. [bib] [pdf] [abstract]|
Position estimation based on distances is a well understood problem. This document describes a simple way to linearize the position equation. Based on the linearization the problem is solved step by step using least squares. This paper includes an example implementation in Matlab.
|||Comparison and Performance Evaluation of Indoor Localization Algorithms based on an Error Model for an Optical System , GRIN (T. M. Buzug et. al., ed.), 2015. [bib]|
|||Localization of Heart Reference Point of a Lying Patient with Microsoft Kinect Sensor , GRIN (T. M. Buzug et. al., ed.), 2014. [bib]|
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