Multiple Frequency Bands for Localization

Duration: 01.01.2014 - 30.08.2016
Project Leader: Prof. Dr.-Ing Horst Hellbrück
Staff: Mathias Pelka


Precision and reliability for localization can be achieved using time of arrival measurements. This method uses short data packets at microwave frequencies. It is possible to calculate the current position using the known speed of light constant. To achieve a spatial resolution in the domain of one food, synchronization should be in the domain of one nano second.


It is desired to develop a system to measure the spatial coordinates of an object. Depending on the size and other parameters of the facilities the system will choose out of three available frequency ranges. Those ranges are 900 MHz, 2.4 GHz and 5.8 GHz. It is desired to use consumer of the shelf products. The radio chips and the antenna should be replaceable via breakout boards. Using that technique, it is possible to reduce the required amount of time to deploy the system.


The purpose of this R&D project is to use common radio chips which are capable of using multiple frequency bands. Those chips will be used to achieve very precise spatial measurement. Using standardization techniques it should be possible to find at least two radio chips, which are out of one chip family. This will help reduce cost and will save development time.

Student Work in this Research Project

There is always a need for students who wants to participate with out our. Currently we are offering the following projects. If you have suggestions for an own project, just write an email

Completed Work:

  • Position Algorithm Simulation(Zhao Lifang)
  • Graphical Codes (Daniel Neckel)
  • Distance estimation for a mobile robot platform with Microsoft Kinect(Lihuan Pan)
  • Graphical Navigation (Peter Lucht)
  • Development of a TDoA System (Swen Leugner)
  • Eine Client-Server-basierte Anwendung zur Navigation auf Basis von QR-Codes (Marco Buchholz)


During the m:flo project a number positioning technologies have been evaluated and tested. For instance, we investigated CSS-based and UWB-based commercial positioning system. We evaluate such positioning systems and distance measurement systems with our tools. For instance, we are able to measure waveforms with our precise 20 GHz Oscilloscope. Such measurements are useful to detect distortions of UWB signals. 

Time domain measurements of a UWB-pulse

When investigating positioning data (for instance, ranging data), a visualization helps to keep track of tags and to get an idea of the quality of a position. We can test algorithms and evaluate the performance with such a system. We get immediately feedback from the system. 

This shows a positioning system in our lab. The position of the tag is shown with the blue line.


For this positioning system a self-developed time-based UWB system is employed. This system features high update rates (> 200 Hz), high accuracy (<0.3m) and high scalability (over 50 tags at the same instance of time).

Project Partners



Förderkennzeichen: KF3177201ED3



Refereed Articles and Book Chapters
[2016] Survey of challenges and towards a unified architecture for location systems (Mathias Pelka, Horst Hellbrück), 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.
[2016] Iterative approach for anchor configuration of positioning systems (Mathias Pelka, Grigori Goronzy, Horst Hellbrück), 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.
[2014] FULFILL - Framework zur Visualisierung, Speicherung und Filterung von Lokalisierungs-Messdaten (Lenka Hanesova, Horst Hellbrück), In ImpulsE, volume 18, 2014. [bib]
Refereed Conference Papers
[2016] S-TDoA - Sequential Time Difference of Arrival - A Scalable and Synchronization Free Approach for Positioning (Mathias Pelka, Horst Hellbrück), 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.
[2016] Impact of Altitude Difference for Local Positioning Systems and Compensation with Two-Stage Filters (Mathias Pelka, Grigori Goronzy, Horst Hellbrück), 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.
[2016] Introduction, Discussion and Evaluation of Recursive Bayesian Filters for Linear and Nonlinear Filtering Problems in Indoor Localization (Mathias Pelka, Horst Hellbrück), 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.
[2016] Investigation of Anomaly-based Passive Localization with Received Signal Strength for IEEE 802.15.4 (Marco Cimdins, Mathias Pelka, Horst Hellbrück), 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.
[2015] Indoor Localization based on Bi-Phase Measurements for Wireless Sensor Networks (Mathias Pelka, Christian Bollmeyer, Horst Hellbrück), 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.
[2015] Wireless Medical Sensors - Context, Robustness and Safety (Christian Bollmeyer, Mathias Pelka, Hartmut Gehring, Horst Hellbrück), In 49th annual conference of the German Society for Biomedical Engineering (BMT 2015), 2015. [bib]
[2014] Accurate Radio Distance Estimation by Phase Measurements with Multiple Frequencies (Mathias Pelka, Christian Bollmeyer, Horst Hellbrück), 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.
[2014] Evaluation of Radio Based, Optical and Barometric Localization for Indoor Altitude Estimation in Medical Applications (Christian Bollmeyer, Mathias Pelka, Hartmut Gehring, Horst Hellbrück), 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.
Refereed Workshop Papers
[2016] Comparison of wired and wireless synchronization with clock drift compensation suited for U-TDoA localization (Swen Leugner, Mathias Pelka, Horst Hellbrück), 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.
[2015] Mobile Robot Seamless Localization with Localization Optimized QR Codes (Mathias Pelka, Daniel Neckel, Horst Hellbrück), 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
Other Publications
[2017] S-TDoA (Sequential Time Difference of Arrival)-Verfahren zur Positionsermittlung von bewegbaren Objekten durch sequentielle Ankunftszeitdifferenzbestimmung von periodischen Signalen (H. Hellbrück, M. Pelka), EP Patent App. EP20,170,157,702 Google Patents, 2017. [bib] [pdf]
[2016] Investigation of Anomaly-based Passive Localization with IEEE 802.15.4 (Marco Cimdins, Mathias Pelka, Horst Hellbrück), Technical report, RWTH Aachen University, 2016. [bib] [pdf]
[2015] Position Calculation with Least Squares based on Distance Measurements (Mathias Pelka), 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.
[2015] Comparison and Performance Evaluation of Indoor Localization Algorithms based on an Error Model for an Optical System (Z. Lifang, M. Pelka, C. Bollmeyer, H. Hellbrück), GRIN (T. M. Buzug et. al., ed.), 2015. [bib]
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