Range-only SLAM with a mobile robot and a Wireless Sensor Networks

This paper presents the localization of a mobile robot while simultaneously mapping the position of the nodes of a Wireless Sensor Network using only range measurements. The robot can estimate the distance to nearby nodes of the Wireless Sensor Network by measuring the Received Signal Strength Indicator (RSSI) of the received radio messages. The RSSI measure is very noisy, especially in an indoor environment due to interference and reflections of the radio signals. We adopted an Extended Kalman Filter SLAM algorithm to integrate RSSI measurements from the different nodes over time, while the robot moves in the environment. A simple pre-processing filter helps in reducing the RSSI variations due to interference and reflections. Successful experiments are reported in which an average localization error less than 1 m is obtained when the SLAM algorithm has no a priori knowledge on the wireless node positions, while a localization error less than 0.5 m can be achieved when the position of the node is initialized close to the their actual position. These results are obtained using a generic path loss model for the transmission channel. Moreover, no internode communication is necessary in the WSN. This can save energy and enables to apply the proposed system also to fully disconnected networks

SCORE: A Second-Order Conic Initialization for Range-Aided SLAM

We present a novel initialization technique for the range-aided simultaneous localization and mapping (RA-SLAM) problem. In RA-SLAM we consider measurements of point-to-point distances in addition to measurements of rigid transformations to landmark or pose variables. Standard formulations of RA-SLAM approach the problem as non-convex optimization, which requires a good initialization to obtain quality results. The initialization technique proposed here relaxes the RA-SLAM problem to a convex problem which is then solved to determine an initialization for the original, non-convex problem. The relaxation is a second-order cone program (SOCP), which is derived from a quadratically constrained quadratic program (QCQP) formulation of the RA-SLAM problem. As a SOCP, the method is highly scalable. We name this relaxation Second-order COnic RElaxation for RA-SLAM (SCORE). To our knowledge, this work represents the first convex relaxation for RA-SLAM. We present real-world and simulated experiments which show SCORE initialization permits the efficient recovery of quality solutions for a variety of challenging single- and multi-robot RA-SLAM problems with thousands of poses and range measurements.Comment: 9 pages, 8 figures, extended version of paper submitted to ICRA 202

Shapes from Echoes: Uniqueness from Point-to-Plane Distance Matrices

We study the problem of localizing a configuration of points and planes from the collection of point-to-plane distances. This problem models simultaneous localization and mapping from acoustic echoes as well as the notable "structure from sound" approach to microphone localization with unknown sources. In our earlier work we proposed computational methods for localization from point-to-plane distances and noted that such localization suffers from various ambiguities beyond the usual rigid body motions; in this paper we provide a complete characterization of uniqueness. We enumerate equivalence classes of configurations which lead to the same distance measurements as a function of the number of planes and points, and algebraically characterize the related transformations in both 2D and 3D. Here we only discuss uniqueness; computational tools and heuristics for practical localization from point-to-plane distances using sound will be addressed in a companion paper.Comment: 13 pages, 13 figure

Fuzzy Mobile-Robot Positioning in Intelligent Spaces Using Wireless Sensor Networks

This work presents the development and experimental evaluation of a method based on fuzzy logic to locate mobile robots in an Intelligent Space using Wireless Sensor Networks (WSNs). The problem consists of locating a mobile node using only inter-node range measurements, which are estimated by radio frequency signal strength attenuation. The sensor model of these measurements is very noisy and unreliable. The proposed method makes use of fuzzy logic for modeling and dealing with such uncertain information. Besides, the proposed approach is compared with a probabilistic technique showing that the fuzzy approach is able to handle highly uncertain situations that are difficult to manage by well-known localization methods

Target coverage through distributed clustering in directional sensor networks

Maximum target coverage with minimum number of sensor nodes, known as an MCMS problem, is an important problem in directional sensor networks (DSNs). For guaranteed coverage and event reporting, the underlying mechanism must ensure that all targets are covered by the sensors and the resulting network is connected. Existing solutions allow individual sensor nodes to determine the sensing direction for maximum target coverage which produces sensing coverage redundancy and much overhead. Gathering nodes into clusters might provide a better solution to this problem. In this paper, we have designed distributed clustering and target coverage algorithms to address the problem in an energy-efficient way. To the best of our knowledge, this is the first work that exploits cluster heads to determine the active sensing nodes and their directions for solving target coverage problems in DSNs. Our extensive simulation study shows that our system outperforms a number of state-of-the-art approaches

An Improved Otsu Threshold Segmentation Method for Underwater Simultaneous Localization and Mapping-Based Navigation

The main focus of this paper is on extracting features with SOund Navigation And Ranging (SONAR) sensing for further underwater landmark-based Simultaneous Localization and Mapping (SLAM). According to the characteristics of sonar images, in this paper, an improved Otsu threshold segmentation method (TSM) has been developed for feature detection. In combination with a contour detection algorithm, the foreground objects, although presenting different feature shapes, are separated much faster and more precisely than by other segmentation methods. Tests have been made with side-scan sonar (SSS) and forward-looking sonar (FLS) images in comparison with other four TSMs, namely the traditional Otsu method, the local TSM, the iterative TSM and the maximum entropy TSM. For all the sonar images presented in this work, the computational time of the improved Otsu TSM is much lower than that of the maximum entropy TSM, which achieves the highest segmentation precision among the four above mentioned TSMs. As a result of the segmentations, the centroids of the main extracted regions have been computed to represent point landmarks which can be used for navigation, e.g., with the help of an Augmented Extended Kalman Filter (AEKF)-based SLAM algorithm. The AEKF-SLAM approach is a recursive and iterative estimation-update process, which besides a prediction and an update stage (as in classical Extended Kalman Filter (EKF)), includes an augmentation stage. During navigation, the robot localizes the centroids of different segments of features in sonar images, which are detected by our improved Otsu TSM, as point landmarks. Using them with the AEKF achieves more accurate and robust estimations of the robot pose and the landmark positions, than with those detected by the maximum entropy TSM. Together with the landmarks identified by the proposed segmentation algorithm, the AEKF-SLAM has achieved reliable detection of cycles in the map and consistent map update on loop closure, which is shown in simulated experiments

Design and Evaluation of Compression, Classification and Localization Schemes for Various IoT Applications

Nowadays we are surrounded by a huge number of objects able to communicate, read information such as temperature, light or humidity, and infer new information through ex- changing data. These kinds of objects are not limited to high-tech devices, such as desktop PC, laptop, new generation mobile phone, i.e. smart phone, and others with high capabilities, but also include commonly used object, such as ID cards, driver license, clocks, etc. that can made smart by allowing them to communicate. Thus, the analog world of just a few years ago is becoming the a digital world of the Inter- net of Things (IoT), where the information from a single object can be retrieved from the Internet. The IoT paradigm opens several architectural challenges, including self-organization, self-managing, self-deployment of the smart objects, as well as the problem of how to minimize the usage of the limited resources of each device. The concept of IoT covers a lot of communication paradigms such as WiFi, Radio Frequency Identification (RFID), and Wireless Sensor Network (WSN). Each paradigm can be thought of as an IoT island where each device can communicate directly with other devices. The thesis is divided in sections in order to cover each problem mentioned above. The first step is to understand the possibility to infer new knowledge from the deployed device in a scenario. For this reason, the research is focused on the web semantic, web 3.0, to assign a semantic meaning to each thing inside the architecture. The sole semantic concept is unusable to infer new information from the data gathered; in fact, it is necessary to organize the data through a hierarchical form defined by an Ontology. Through the exploitation of the Ontology, it is possible to apply semantic engine reasoners to infer new knowledge about the network. The second step of the dissertation deals with the minimization of the usage of every node in a WSN. The main purpose of each node is to collect environmental data and to exchange hem with other nodes. To minimize battery consumption, it is necessary to limit the radio usage. Therefore, we implemented Razor, a new lightweight algorithm which is expected to improve data compression and classification by leveraging on the advantages offered by data mining methods for optimizing communications and by enhancing information transmission to simplify data classification. Data compression is performed studying the well-know Vector Quantization (VQ) theory in order to create the codebooks necessary for signal compression. At the same time, it is requested to give a semantic meaning to un- known signals. In this way, the codebook feature is able not only to compress the signals, but also to classify unknown signals. Razor is compared with both state-of-the-art compression and signal classification techniques for WSN . The third part of the thesis covers the concept of smart object applied to Robotic research. A critical issue is how a robot can localize and retrieve smart objects in a real scenario without any prior knowledge. In order to achieve the objectives, it is possible to exploit the smart object concept and localize them through RSSI measurements. After the localization phase, the robot can exploit its own camera to retrieve the objects. Several filtering algorithms are developed in order to mitigate the multi–path issue due to the wireless communication channel and to achieve a better distance estimation through the RSSI measurement. The last part of the dissertation deals with the design and the development of a Cognitive Network (CN) testbed using off the shelf devices. The device type is chosen considering the cost, usability, configurability, mobility and possibility to modify the Operating System (OS) source code. Thus, the best choice is to select some devices based on Linux kernel as Android OS. The feature to modify the Operating System is required to extract the TCP/IP protocol stack parameters for the CN paradigm. It is necessary to monitor the network status in real-time and to modify the critical parameters in order to improve some performance, such as bandwidth consumption, number of hops to exchange the data, and throughput

Automatisierte Integration von funkbasierten Sensornetzen auf Basis simultaner Lokalisierung und Kartenerstellung

Ziel der vorliegenden Arbeit ist die Entwicklung eines Verfahrens zur automatisierten Integration funkbasierter drahtloser Sensornetze (engl. Wireless Sensor Network, kurz WSN) in die jeweilige Anwendungsumgebung. Die Sensornetze realisieren dort neben Kommunikationsaufgaben vor allem die Bestimmung von Ortsinformationen. Das Betriebshofmanagement im ÖPNV stellt dabei eine typische Anwendung dar. So wird auf der Grundlage permanent verfügbarer Positionskoordinaten von Bussen und Bahnen als mobile Objekte im Verkehrsumfeld eine effizientere Betriebsführung ermöglicht. Die Datenbasis in dieser Arbeit bilden zum einen geometrische Beziehungen im Sensornetz, die aus Gründen der Verfügbarkeit lediglich durch paarweise Distanzen zwischen den mobilen Objekten und den im Umfeld fest installierten Ankern beschrieben sind. Zum anderen kann auf vorhandenes digitales Kartenmaterial in Form von Vektor- und Rasterkarten bspw. von GIS-Diensten zurückgegriffen werden. Die Argumente für eine Automatisierung sind naheliegend. Einerseits soll der Aufwand der Positionskalibrierung nicht mit der Anzahl verbauter Anker skalieren, was sich ausschließlich automatisiert realisieren lässt. Dadurch werden gleichzeitig symptomatische Fehlerquellen, die aus einer manuellen Systemintegration resultieren, eliminiert. Andererseits soll die Automatisierung ein echtzeitfähiges Betreiben (z.B. Rekalibrierung und Fernwartung) gewährleisten, sodass kostenintensive Wartungs- und Servicedienstleistungen entfallen. Das entwickelte Verfahren generiert zunächst aus den Sensordaten mittels distanzbasierter simultaner Lokalisierung und Kartenerstellung (engl. Range-Only Simultaneous Localization and Mapping, kurz RO-SLAM) relative Positionsinformationen für Anker und mobile Objekte. Anschließend führt das Verfahren diese Informationen im Rahmen einer kooperativen Kartenerstellung zusammen. Aus den relativen, kooperativen Ergebnissen und dem zugrundeliegenden Kartenmaterial wird schließlich ein anwendungsspezifischer absoluter Raumbezug hergestellt. Die Ergebnisse der durchgeführten Verfahrensevaluation belegen anhand generierter semi-realer Sensordaten sowie definierter Testszenarien die Funktions- und Leistungsfähigkeit des entwickelten Verfahrens. Sie beinhalten qualifizierende Aussagen und zeigen darüber hinaus statistisch belastbare Genauigkeitsgrenzen auf.:Abbildungsverzeichnis...............................................X Tabellenverzeichnis...............................................XII Abkürzungsverzeichnis............................................XIII Symbolverzeichnis................................................XVII 1 Einleitung........................................................1 1.1 Stand der Technik...............................................3 1.2 Entwickeltes Verfahren im Überblick.............................4 1.3 Wissenschaftlicher Beitrag......................................7 1.4 Gliederung der Arbeit...........................................8 2 Grundlagen zur Verfahrensumsetzung...............................10 2.1 Überblick zu funkbasierten Sensornetzen........................10 2.1.1 Aufbau und Netzwerk..........................................11 2.1.2 System- und Technologiemerkmale..............................12 2.1.3 Selbstorganisation...........................................13 2.1.4 Räumliche Beziehungen........................................14 2.2 Umgebungsrepräsentation........................................18 2.2.1 Koordinatenbeschreibung......................................19 2.2.2 Kartentypen..................................................20 2.3 Lokalisierung..................................................22 2.3.1 Positionierung...............................................23 2.3.2 Tracking.....................................................28 2.3.3 Koordinatentransformation....................................29 3 Zustandsschätzung dynamischer Systeme............................37 3.1 Probabilistischer Ansatz.......................................38 3.1.1 Satz von Bayes...............................................39 3.1.2 Markov-Kette.................................................40 3.1.3 Hidden Markov Model..........................................42 3.1.4 Dynamische Bayes‘sche Netze..................................43 3.2 Bayes-Filter...................................................45 3.2.1 Extended Kalman-Filter.......................................48 3.2.2 Histogramm-Filter............................................51 3.2.3 Partikel-Filter..............................................52 3.3 Markov Lokalisierung...........................................58 4 Simultane Lokalisierung und Kartenerstellung.....................61 4.1 Überblick......................................................62 4.1.1 Objektbeschreibung...........................................63 4.1.2 Umgebungskarte...............................................65 4.1.3 Schließen von Schleifen......................................70 4.2 Numerische Darstellung.........................................72 4.2.1 Formulierung als Bayes-Filter................................72 4.2.2 Diskretisierung des Zustandsraums............................74 4.2.3 Verwendung von Hypothesen....................................74 4.3 Initialisierung des Range-Only SLAM............................75 4.3.1 Verzögerte und unverzögerte Initialisierung..................75 4.3.2 Initialisierungsansätze......................................76 4.4 SLAM-Verfahren.................................................80 4.4.1 Extended Kalman-Filter-SLAM..................................81 4.4.2 Incremental Maximum Likelihood-SLAM..........................90 4.4.3 FastSLAM.....................................................99 5 Kooperative Kartenerstellung....................................107 5.1 Aufbereitung der Ankerkartierungsergebnisse...................108 5.2 Ankerkarten-Merging-Verfahren.................................110 5.2.1 Auflösen von Mehrdeutigkeiten...............................110 5.2.2 Erstellung einer gemeinsamen Ankerkarte.....................115 6 Herstellung eines absoluten Raumbezugs..........................117 6.1 Aufbereitung der Lokalisierungsergebnisse.....................117 6.1.1 Generierung von Geraden.....................................119 6.1.2 Generierung eines Graphen...................................122 6.2 Daten-Matching-Verfahren......................................123 6.2.1 Vektorbasierte Karteninformationen..........................125 6.2.2 Rasterbasierte Karteninformationen..........................129 7 Verfahrensevaluation............................................133 7.1 Methodischer Ansatz...........................................133 7.2 Datenbasis....................................................135 7.2.1 Sensordaten.................................................137 7.2.2 Digitales Kartenmaterial....................................143 7.3 Definition von Testszenarien..................................145 7.4 Bewertung.....................................................147 7.4.1 SLAM-Verfahren..............................................148 7.4.2 Ankerkarten-Merging-Verfahren...............................151 7.4.3 Daten-Matching-Verfahren....................................152 8 Zusammenfassung und Ausblick....................................163 8.1 Ergebnisse der Arbeit.........................................164 8.2 Ausblick......................................................165 Literaturverzeichnis..............................................166 A Ergänzungen zum entwickelten Verfahren..........................A-1 A.1 Generierung von Bewegungsinformationen........................A-1 A.2 Erweiterung des FastSLAM-Verfahrens...........................A-2 A.3 Ablauf des konzipierten Greedy-Algorithmus....................A-4 A.4 Lagewinkel der Kanten in einer Rastergrafik...................A-5 B Ergänzungen zur Verfahrensevaluation............................A-9 B.1 Geschwindigkeitsprofile der simulierten Objekttrajektorien....A-9 B.2 Gesamtes SLAM-Ergebnis eines Testszenarios....................A-9 B.3 Statistische Repräsentativität...............................A-10 B.4 Gesamtes Ankerkarten-Merging-Ergebnis eines Testszenarios....A-11 B.5 Gesamtes Daten-Matching-Ergebnis eines Testszenarios.........A-18 B.6 Qualitative Ergebnisbewertung................................A-18 B.7 Divergenz des Gesamtverfahrens...............................A-18The aim of this work is the development of a method for the automated integration of Wireless Sensor Networks (WSN) into the respective application environment. The sensor networks realize there beside communication tasks above all the determination of location information. Therefore, the depot management in public transport is a typical application. Based on permanently available position coordinates of buses and trams as mobile objects in the traffic environment, a more efficient operational management is made possible. The database in this work is formed on the one hand by geometric relationships in the sensor network, which for reasons of availability are only described by pairwise distances between the mobile objects and the anchors permanently installed in the environment. On the other hand, existing digital map material in the form of vector and raster maps, e.g. obtained by GIS services, is used. The arguments for automation are obvious. First, the effort of position calibration should not scale with the number of anchors installed, which can only be automated. This at once eliminates symptomatic sources of error resulting from manual system integration. Secondly, automation should ensure real-time operation (e.g. recalibration and remote maintenance), eliminating costly maintenance and service. Initially, the developed method estimates relative position information for anchors and mobile objects from the sensor data by means of Range-Only Simultaneous Localization and Mapping (RO-SLAM). The method then merges this information within a cooperative map creation. From the relative, cooperative results and the available map material finally an application-specific absolute spatial outcome is generated. Based on semi-real sensor data and defined test scenarios, the results of the realized method evaluation demonstrate the functionality and performance of the developed method. They contain qualifying statements and also show statistically reliable limits of accuracy.:Abbildungsverzeichnis...............................................X Tabellenverzeichnis...............................................XII Abkürzungsverzeichnis............................................XIII Symbolverzeichnis................................................XVII 1 Einleitung........................................................1 1.1 Stand der Technik...............................................3 1.2 Entwickeltes Verfahren im Überblick.............................4 1.3 Wissenschaftlicher Beitrag......................................7 1.4 Gliederung der Arbeit...........................................8 2 Grundlagen zur Verfahrensumsetzung...............................10 2.1 Überblick zu funkbasierten Sensornetzen........................10 2.1.1 Aufbau und Netzwerk..........................................11 2.1.2 System- und Technologiemerkmale..............................12 2.1.3 Selbstorganisation...........................................13 2.1.4 Räumliche Beziehungen........................................14 2.2 Umgebungsrepräsentation........................................18 2.2.1 Koordinatenbeschreibung......................................19 2.2.2 Kartentypen..................................................20 2.3 Lokalisierung..................................................22 2.3.1 Positionierung...............................................23 2.3.2 Tracking.....................................................28 2.3.3 Koordinatentransformation....................................29 3 Zustandsschätzung dynamischer Systeme............................37 3.1 Probabilistischer Ansatz.......................................38 3.1.1 Satz von Bayes...............................................39 3.1.2 Markov-Kette.................................................40 3.1.3 Hidden Markov Model..........................................42 3.1.4 Dynamische Bayes‘sche Netze..................................43 3.2 Bayes-Filter...................................................45 3.2.1 Extended Kalman-Filter.......................................48 3.2.2 Histogramm-Filter............................................51 3.2.3 Partikel-Filter..............................................52 3.3 Markov Lokalisierung...........................................58 4 Simultane Lokalisierung und Kartenerstellung.....................61 4.1 Überblick......................................................62 4.1.1 Objektbeschreibung...........................................63 4.1.2 Umgebungskarte...............................................65 4.1.3 Schließen von Schleifen......................................70 4.2 Numerische Darstellung.........................................72 4.2.1 Formulierung als Bayes-Filter................................72 4.2.2 Diskretisierung des Zustandsraums............................74 4.2.3 Verwendung von Hypothesen....................................74 4.3 Initialisierung des Range-Only SLAM............................75 4.3.1 Verzögerte und unverzögerte Initialisierung..................75 4.3.2 Initialisierungsansätze......................................76 4.4 SLAM-Verfahren.................................................80 4.4.1 Extended Kalman-Filter-SLAM..................................81 4.4.2 Incremental Maximum Likelihood-SLAM..........................90 4.4.3 FastSLAM.....................................................99 5 Kooperative Kartenerstellung....................................107 5.1 Aufbereitung der Ankerkartierungsergebnisse...................108 5.2 Ankerkarten-Merging-Verfahren.................................110 5.2.1 Auflösen von Mehrdeutigkeiten...............................110 5.2.2 Erstellung einer gemeinsamen Ankerkarte.....................115 6 Herstellung eines absoluten Raumbezugs..........................117 6.1 Aufbereitung der Lokalisierungsergebnisse.....................117 6.1.1 Generierung von Geraden.....................................119 6.1.2 Generierung eines Graphen...................................122 6.2 Daten-Matching-Verfahren......................................123 6.2.1 Vektorbasierte Karteninformationen..........................125 6.2.2 Rasterbasierte Karteninformationen..........................129 7 Verfahrensevaluation............................................133 7.1 Methodischer Ansatz...........................................133 7.2 Datenbasis....................................................135 7.2.1 Sensordaten.................................................137 7.2.2 Digitales Kartenmaterial....................................143 7.3 Definition von Testszenarien..................................145 7.4 Bewertung.....................................................147 7.4.1 SLAM-Verfahren..............................................148 7.4.2 Ankerkarten-Merging-Verfahren...............................151 7.4.3 Daten-Matching-Verfahren....................................152 8 Zusammenfassung und Ausblick....................................163 8.1 Ergebnisse der Arbeit.........................................164 8.2 Ausblick......................................................165 Literaturverzeichnis..............................................166 A Ergänzungen zum entwickelten Verfahren..........................A-1 A.1 Generierung von Bewegungsinformationen........................A-1 A.2 Erweiterung des FastSLAM-Verfahrens...........................A-2 A.3 Ablauf des konzipierten Greedy-Algorithmus....................A-4 A.4 Lagewinkel der Kanten in einer Rastergrafik...................A-5 B Ergänzungen zur Verfahrensevaluation............................A-9 B.1 Geschwindigkeitsprofile der simulierten Objekttrajektorien....A-9 B.2 Gesamtes SLAM-Ergebnis eines Testszenarios....................A-9 B.3 Statistische Repräsentativität...............................A-10 B.4 Gesamtes Ankerkarten-Merging-Ergebnis eines Testszenarios....A-11 B.5 Gesamtes Daten-Matching-Ergebnis eines Testszenarios.........A-18 B.6 Qualitative Ergebnisbewertung................................A-18 B.7 Divergenz des Gesamtverfahrens...............................A-1