kth.sePublications
Change search
Refine search result
12 1 - 50 of 69
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Bengtsson, Mats
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Lilliesköld, Joakim
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Norgren, Martin
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Sohlström, Hans
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Developing and Implementing a Program Interfacing Project Course in Electrical Engineering2012Conference paper (Refereed)
    Abstract [en]

    In this paper, we describe the ideas behind a second-year Design-Build course in Electrical Engineering. Electrical Engineering is a theoretical subject, and in such it is difficult to maintain the theoretical level in project courses introduced too early in the program, especially when core subjects like electromagnetic field theory are involved. This issue is addressed and we also describe our approach for the assessment of the students. We also discuss the different goals that were set up prior to the course from a program perspective; how we reasoned when designing the course, the assessment structure, and the output once the course was implemented

  • 2.
    Carlsson, Håkan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems.
    Skog, Isaac
    Linköping University, The Institute of Technology.
    Hendeby, Gustaf
    Linköping University, The Institute of Technology.
    Jaldén, Joakim
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Inertial Navigation Using an Inertial Sensor ArrayManuscript (preprint) (Other academic)
    Abstract [en]

    We present a comprehensive framework for fusing measurements from multiple and generally placed accelerometers and gyroscopes to perform inertial navigation. Using the angular acceleration provided by the accelerometer array, we show that the numerical integration of the orientation can be done with second-order accuracy, which is more accurate compared to the traditional first-order accuracy that can be achieved when only using the gyroscopes. Since orientation errors are the most significant error source in inertial navigation,  improving the orientation estimation reduces the overall navigation error. The practical performance benefit depends on prior knowledge of the inertial sensor array, and therefore we present four different state-space models using different underlying assumptions regarding the orientation modeling. The models are evaluated using a  Lie Group Extended Kalman filter through simulations and real-world experiments.  We also show how individual accelerometer biases are unobservable and can be replaced by a six-dimensional bias term whose dimension is fixed and independent of the number of accelerometers.

    Download full text (pdf)
    fulltext
  • 3.
    Carlsson, Håkan
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Jaldén, Joakim
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    On-The-Fly Geometric Calibration of Inertial Sensor Arrays2017In: Proceedings 2017 international conference on indoor positioning and indoor navigation (IPIN), Institute of Electrical and Electronics Engineers (IEEE) , 2017Conference paper (Refereed)
    Abstract [en]

    We present a maximum likelihood estimator for estimating the positions of accelerometers in an inertial sensor array. This method simultaneously estimates the positions of the accelerometers and the motion dynamics of the inertial sensor array and, therefore, does not require a predefined motion sequence nor any external equipment. Using an iterative block coordinate descent optimization strategy, the calibration problem can be solved with a complexity that is linear in the number of time samples. The proposed method is evaluated by Monte-Carlo simulations of an inertial sensor array built out of 32 inertial measurement units. The simulation results show that, if the array experiences sufficient dynamics, the position error is inversely proportional to the number of time samples used in the calibration sequence. Further, results show that for the considered array geometry and motion dynamics in the order of 2000 degrees/s and 2000 degrees/s(2), the positions of the accelerometers can be estimated with an accuracy in the order of 10(-6) m using only 1000 time samples. This enables fast on-the-fly calibration of the geometric errors in an inertial sensor array by simply twisting it by hand for a few seconds.

  • 4.
    Carlsson, Håkan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems.
    Skog, Isaac
    Linköping Univ, Dept Elect Engn, S-58183 Linköping, Sweden..
    Jaldén, Joakim
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Self-Calibration of Inertial Sensor Arrays2021In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 21, no 6, p. 8451-8463Article in journal (Refereed)
    Abstract [en]

    A maximum likelihood estimator is presented for self-calibrating both accelerometers and gyroscopes in an inertial sensor array, including scale factors, misalignments, biases, and sensor positions. By simultaneous estimation of the calibration parameters and the motion dynamics of the array, external equipment is not required for the method. A computational efficient iterative optimization method is proposed where the calibration problem is divided into smaller subproblems. Further, an identifiability analysis of the calibration problem is presented. The analysis shows that it is sufficient to know the magnitude of the local gravity vector and the average scale factor gain of the gyroscopes, and that the array is exposed to two types of motions for the calibration problem to be well defined. The proposed estimator is evaluated by real-world experiments and by Monte Carlo simulations. The results show that the parameters can be consistently estimated and that the calibration significantly improves the accuracy of the motion estimation. This enables on-the-fly calibration of small inertial sensors arrays by simply twisting them by hand.

  • 5.
    Carlsson, Håkan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems.
    Skog, Isaac
    Linköping Univ LIU, Dept Elect Engn, S-58183 Linköping, Sweden..
    Schön, Thomas B.
    Uppsala Univ, Dept Informat Technol, S-75236 Uppsala, Sweden..
    Jaldén, Joakim
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems.
    Quantifying the Uncertainty of the Relative Geometry in Inertial Sensors Arrays2021In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 21, no 17, p. 19362-19373Article in journal (Refereed)
    Abstract [en]

    We present an algorithm to estimate and quantify the uncertainty of the accelerometers' relative geometry in an inertial sensor array. We formulate the calibration problem as a Bayesian estimation problem and propose an algorithm that samples the accelerometer positions' posterior distribution using Markov chain Monte Carlo. By identifying linear substructures of the measurement model, the unknown linear motion parameters are analytically marginalized, and the remaining non-linear motion parameters are numerically marginalized. The numerical marginalization occurs in a low dimensional space where the gyroscopes give information about the motion. This combination of information from gyroscopes and analytical marginalization allows the user to make no assumptions of the motion before the calibration. It thus enables the user to estimate the accelerometer positions' relative geometry by simply exposing the array to arbitrary twisting motion. We show that the calibration algorithm gives good results on both simulated and experimental data, despite sampling a high dimensional space.

    Download full text (pdf)
    fulltext
  • 6.
    De Angelis, Alessio
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Nilsson, John Olof
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Carbone, P.
    Indoor positioning by ultra wide band radio aided inertial navigation2009In: 19th IMEKO World Congress 2009, 2009, p. 450-455Conference paper (Refereed)
    Abstract [en]

    In this paper, a research activity aimed at developing an indoor positioning system is presented. The realized system prototype uses sensor fusion techniques to combine information from two sources: a local Ultra-Wideband (UWB) radio based distance-measuring system infrastructure and an Inertial Navigation System (INS). The UWB system provides a measure of distance between two transceivers by measuring the time-of-flight of pulses. Its principle of operation is briefly described, together with the main features of its architecture. Furthermore, the main characteristics of the INS and of the Extended Kalman Filter information fusion approach are presented. Finally, some experimental results are provided, relative to static and dynamic position measurements.

  • 7.
    De Angelis, Alessio
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nilsson, John Olof
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Carbone, Paolo
    Indoor positioning by ultra wide band radio aided inertial navigation2010In: Metrology and Measurement Systems, ISSN 0860-8229, Vol. 17, no 3, p. 447-460Article in journal (Refereed)
    Abstract [en]

    A research study aimed at developing a novel indoor positioning system is presented. The realized system prototype uses sensor fusion techniques to combine information from two sources: an in-house developed local Ultra-Wideband (UWB) radio-based ranging system and an inertial navigation system (INS). The UWB system measures the distance between two transceivers by recording the round-trip-time (RTT) of UWB radio pulses. Its principle of operation is briefly described, together with the main design features. Furthermore, the main characteristics of the INS and of the Extended Kalman Filter information fusion approach are presented. Finally, selected static and dynamic test scenario experimental results are provided. In particular, the advantages of the proposed information fusion approach are further investigated by means of a high dynamic test scenario.

  • 8.
    De Angelis, Alessio
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Nilsson, John-Olof
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    UWB Ranging Hardware Platform2010In: GigaHertz Symposium, Lund, Sweden, 2010Conference paper (Other academic)
  • 9. Gupta, Amit K.
    et al.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Long-term Performance Evaluation of a Foot-mounted Pedestrian Navigation Device2015In: 2015 ANNUAL IEEE INDIA CONFERENCE (INDICON), 2015Conference paper (Refereed)
    Abstract [en]

    In this paper, we present a long term experimental study performed on a foot mounted pedestrian navigation device, the Osmium MIMU22BTP, which is based on the OpenShoe platform. The aim of the study is to investigate the performance that can be expected in mass market applications. Accordingly, we investigate the error characteristics over a large number of tracking devices and their alternative mounting schemes, over several wearers, and over different walking scenarios. By a massive data collection corresponding to more than 150 km of elapsed walking distance over almost 1,000 independent tests, the law of large numbers provides us with illustrative rule-of-thumbs for the tracking performance in realistic use cases. We observe no outlier performance and relative errors less than 4% in 95% of the test-cases, indicating its potential for a variety of indoor Location Based Services (LBS) and IoT applications based on foot-mounted inertial sensing and dead reckoning. The experimental findings are validated with long distance walks.

  • 10.
    Hari, K.V.S.
    et al.
    Indian Institute of Science (IISc).
    Nilsson, John-Olof
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rantakokko, Jouni
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Prateek, G.V.
    Indian Institute of Science (IISc).
    A prototype of a first-responder indoor localization system2013In: Journal of the Indian Institute of Science, ISSN 0970-4140, Vol. 93, no 3, p. 511-520Article, review/survey (Refereed)
    Abstract [en]

    In this paper we present an approach to build a prototype. model of a first-responder localization system intended for disaster relief operations. This system is useful to monitor and track the positions of the first-responders in an indoor environment, where GPS is not available. Each member of the first responder team is equipped with two zero-velocity-update-aided inertial navigation systems, one on each foot, a camera mounted on a helmet, and a processing platform strapped around the waist of the first responder, which fuses the data from the different sensors. The fusion algorithm runs real-time on the processing platform. The video is also processed using the DSP core of the computing machine. The processed data consisting of position, velocity, heading information along with video streams is transmitted to the command and control system via a local infrastructure WiFi network. A centralized cooperative localization algorithm, utilizing the information from Ultra Wideband based inter-agent ranging devices combined with the position estimates and uncertainties of each first responder, has also been implemented.

  • 11.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Movelo AB, Sweden.
    Ohlsson, Jens
    Stockholm University.
    Ohlsson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Movelo AB, Sweden.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. Movelo AB, Sweden.
    Nygren, Elin
    Smartphone-Based Measurement Systems for Road Vehicle Traffic Monitoring and Usage-Based Insurance2014In: IEEE Systems Journal, ISSN 1932-8184, E-ISSN 1937-9234, Vol. 8, no 4, p. 1238-1248Article in journal (Refereed)
    Abstract [en]

    A framework is presented to deploy a smartphone-based measurement system for road vehicle traffic monitoring and usage-based insurance (UBI). Through the aid of a hierarchical model to modularize the description, the functionality is described as spanning from sensor-level functionality and technical specification to the topmost business model. The designer of a complex measurement system has to consider the full picture from low-level sensing, actuating, and wireless data transfer to the topmost level, including enticements for the individual smartphone owners, i.e., the end users who are the actual measurement probes. The measurement system provides two data streams: a primary stream to support road vehicle traffic monitoring and a secondary stream to support the UBI program. The former activity has a clear value for a society and its inhabitants, as it may reduce congestion and environmental impacts. The latter data stream drives the business model and parts of the revenue streams, which ensure the funding of the total measurement system and create value for the end users, the service provider, and the insurance company. In addition to the presented framework, outcome from a measurement campaign is presented, including road vehicle traffic monitoring (primary data stream) and a commercial pilot of UBI based on the driver profiles (secondary data stream). The measurement system is believed to be sustainable due to the incitements offered to the individual end users, in terms of favorable pricing for the insurance premium. The measurement campaign itself is believed to have an interest in its own right, as it includes smartphone probing of road traffic with a number of probes in the vicinity of the current state of the art, given by the Berkeley Mobile Millennium Project. During the ten-month run of the project, some 4500 driving h/250 000 km of road vehicle traffic data were collected.

    Download full text (pdf)
    fulltext
  • 12.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Martin
    Ohlsson, Jens
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Avläsning och central lagring av mätarställning2012Patent (Other (popular science, discussion, etc.))
  • 13.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Martin
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Jens
    Bestämning av aktivitetsgrad hos portabel elektronisk utrustning2012Patent (Other (popular science, discussion, etc.))
  • 14.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Martin
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Jens
    Determination of activity rate of portable electronic equipment2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A method for obtaining activity rate of a portable electronic device (250) during travel with a vehicle (200) comprises determining (S100) a calculated driving distance based on the portable electronic device utilizing a sequence of measured positions for the portable electronic device. The method further comprises determining (S200) a read driving distance by reading of odometer indication (270) of the vehicle. The method also comprises calculating (S300) an activity rate by comparison of the calculated driving distance with the read driving distance. The method further comprises calculating (S400) a flag which indicates the validity of the calculated activity rate, where the flag is calculated based on the sequence of measured positions for the portable electronic device. The method also comprises transferring (S500) an information packet (280) to a central server (290), where the information packet comprises the activity rate, and/or the read driving distance, and/or the flag.

  • 15.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, J.
    Smartphone instrumentation for insurance telematics2015In: Conference Record - IEEE Instrumentation and Measurement Technology Conference, IEEE Press, 2015, Vol. July, p. 1613-1616Conference paper (Refereed)
    Abstract [en]

    Insurance telematics is a disruptive technology that is expected to reform the vehicle insurance industry. Based on sensor data, the traditional measures for calculating the insurance premium are complemented to determine a fee that more accurately predicts the risk profile of the policyholder. From an instrumentation and measurement point of view, there are several insurance telematics challenges that have to be tackled. It is about consistently extracting relevant figures of merit (FoMs) like number of harsh braking, speeding, heavy cornering, trip smoothness, etc, and then to transform these FoMs into a valid measure, or score, that determines the risk profile of the insurance customer. The paper presents a characterization of FoMs in terms of actuarial relevance, the driver’s influence, stationarity and observability, which are important for the given task. Dedicated hardware to be fitted into the on-board diagnostics outlet as well as contemporary smartphones are two different insurance telematics platforms for data collection. The paper discusses the properties of the smartphone in the perspective of insurance telematics as a low-cost alternative to the hardwired platforms like the one connected to the vehicle’s on-board diagnostics outlet.

  • 16. Händel, Peter
    et al.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Martin
    Ohlsson, Jens
    Anordning för att bestämma identitet hos ett motorfordon2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A device (100) for determining an identity of a vehicle comprises a connector (110) configured to be connected to the cigarette lighter outlet (230) of the vehicle (200). The device further comprises measuring equipment (310; 320; 330) configured to provide an electric signal (400) related to the engine speed of the vehicle, such that oscillations in the electric signal have a frequency proportional to the engine speed of the vehicle. The device is configured to allow determination of an identity of the vehicle based on the electric signal, such that the identity is independent of variations in the engine speed of the vehicle. The device also comprises a memory (340) configured to store the electric signal, and/or the identity of the vehicle.

  • 17.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Wahlström, Johan
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bonawiede, Farid
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Welch, R.
    Ohlsson, J.
    Ohlsson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Insurance telematics: Opportunities and challenges with the smartphone solution2014In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 6, no 4, p. 57-70, article id 6936433Article in journal (Refereed)
    Abstract [en]

    Smartphone-based insurance telematics or usage based insurance is a disruptive technology which relies on insurance premiums that reflect the risk profile of the driver; measured via smartphones with appropriate installed software. A survey of smartphone-based insurance telematics is presented, including definitions; Figure-of-Merits (FoMs), describing the behavior of the driver and the characteristics of the trip; and risk profiling of the driver based on different sets of FoMs. The data quality provided by the smartphone is characterized in terms of Accuracy, Integrity, Availability, and Continuity of Service. The quality of the smartphone data is further compared with the quality of data from traditional in-car mounted devices for insurance telematics, revealing the obstacles that have to be combated for a successful smartphone-based installation, which are the poor integrity and low availability. Simply speaking, the reliability is lacking considering the smartphone measurements. Integrity enhancement of smartphone data is illustrated by both second-by-second lowlevel signal processing to combat outliers and perform integrity monitoring, and by trip-based map-matching for robustification of the recorded trip data. A plurality of FoMs are described, analyzed and categorized, including events and properties like harsh braking, speeding, and location. The categorization of the FoMs in terms of Observability, Stationarity, Driver influence, and Actuarial relevance are tools for robust risk profiling of the driver and the trip. Proper driver feedback is briefly discussed, and rule-of-thumbs for feedback design are included. The work is supported by experimental validation, statistical analysis, and experiences from a recent insurance telematics pilot run in Sweden.

  • 18.
    Händel, Peter
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Yao, Yi
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Unkuri, Nina
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skog, Isaac
    Far infrared camera platform and experiments for moose early warning systems2009In: Transactions of Society of Automotive Engineers of Japan, ISSN 0287-8321, Vol. 40, no 4, p. 1095-1099Article in journal (Refereed)
    Abstract [en]

    Encounters between big game, such as the moose, and private cars often result in severe injuries and death. A vehicle-based moose detection early warning system is a technical countermeasure to increase the traffic safety by alerting the driver in case of danger. Based on available off-the-shelf consumer electronics, a infrared night vision system was built to serve as a platform for experiments with moose early warning driver assistance systems. Aspects of a moose thermal replica employing a horse are discussed and typical vehicle-moose movements are directed and recorded to form a publicly available database for research and education.

    Download full text (pdf)
    fulltext
  • 19.
    Larsson, Robin
    et al.
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Inertial Sensor Driven Smartphone and Automobile Coordinate System Alignment2017In: 2017 IEEE 20TH INTERNATIONAL CONFERENCE ON INTELLIGENT TRANSPORTATION SYSTEMS (ITSC), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    In this study a method is presented for estimating the orientation of an inertial measurement unit (IMU) located within an automobile, using only the measurements from the IMU itself. The orientation estimation problem is posed as a non-linear filtering probletn, which is solved using a marginalized particle filter. The performance of the proposed method is evaluated using a large collection of real-world data, collected by multiple drivers. The drivers used their own smartphones and had no restrictions on smartphone handling during drives. The orientation accuracy achieved with the proposed method is in the order of a few degrees; 50% of cases were below 5 degrees and 90% of cases were below 20 degrees.

  • 20.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    De Angelis, Alessio
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Carbone, Paolo
    Department of Electronic and Information Engineering, University of Perugia.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    SIGNAL PROCESSING ISSUES IN INDOOR POSITIONING BY ULTRA WIDE BAND RADIO AIDED INERTIAL NAVIGATION2009In: Proc. EUSIPCO2009, EURASIP , 2009, p. 2161-2165Conference paper (Refereed)
    Abstract [en]

    The difficulties and possibilities connected to indoor positioning suggest using several sources of navigational information. Apart from the signal processing of the individual sources this gives rise to the need for information fusion. This article aims at presenting and describing the signal processing methods and issues faced when constructing a navigation system based on a local ultra wide band (UWB) ranging system and an inertial navigation system (INS). The signal processing methods within the individual systems are described together with techniques for fusing the information from them. Finally, filtering results of experimental data is presented with expected convergence properties and positioning accuracy of below ±4 cm.

    Download full text (pdf)
    Signal_processing_issues_in_indoor_positioning_by_ultra_wide_band_aided_inertial_navigation
  • 21.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rantakokko, Jouni
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ohlsson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Hari, K.V.S.
    Indian Institute of Science (IISc).
    Accurate Indoor Positioning of Firefighters using Dual Foot-mounted Inertial Sensors and Inter-agent Ranging2014In: Proceedings of the Position, Location and Navigation Symposium (PLANS), 2014 IEEE/ION, 2014Conference paper (Refereed)
    Abstract [en]

    A real-time cooperative localization system,utilizing dual foot-mounted low-cost inertial sensors and RFbasedinter-agent ranging, has been developed. Scenario-basedtests have been performed, using fully-equipped firefightersmimicking a search operation in a partly smoke-filledenvironment, to evaluate the performance of the TOR (TacticallOcatoR) system. The performed tests included realisticfirefighter movements and inter-agent distances, factors that arecrucial in order to provide realistic evaluations of the expectedperformance in real-world operations. The tests indicate that theTOR system may be able to provide a position accuracy ofapproximately two to three meters during realistic firefighteroperations, with only two smoke diving firefighters and onesupervising firefighter within range.

    Download full text (pdf)
    TOR_tests
  • 22.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Inertial Sensor Arrays - A Literature Review2016In: 2016 EUROPEAN NAVIGATION CONFERENCE (ENC), IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    Inertial sensor arrays present the possibility of improved and extended sensing capabilities as compared to customary inertial sensor setups. Inertial sensor arrays have been studied since the 1960s and have recently received a renewed interest, mainly thanks to the ubiquitous micro-electromechanical (MEMS) inertial sensors. However, the number of variants and features of inertial sensor arrays and their disparate applications makes the literature spread out. Therefore, in this paper we provide a brief summary and literature review on the topic of inertial sensor arrays. Publications are categorized and presented in a structured way; references to +300 publications are provide. Finally, an outlook on the main research challenges and opportunities related to inertial sensor arrays is given.

  • 23.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    De Angelis, Alessio
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Aquilanti, Claudia
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Gear scale estimation for synthetic speed pulse generation2011In: 36th IEEE International Conference on Acoustics, Speech, and Signal Processing, IEEE conference proceedings, 2011, p. 1825-1828Conference paper (Refereed)
    Abstract [en]

    In a motorized vehicle a number of easily measurable signals with frequency components related to the rotational speed of the engine can be found, e.g., vibrations, electrical system voltage level, and ambient sound. These signals could potentially be used to estimate the speed and related states of the vehicle. Unfortunately, such estimates would typically require the relations (scale factors) between the frequency components and the speed for different gears to be known. Consequently, in this article we look at the problem of estimating these gear scale factors from training data consisting only of speed measurements and measurements of the signal in question. The estimation problem is formulated as a maximum likelihood estimation problem and heuristics is used to find initial values for a numerical evaluation of the estimator. Finally, a measurement campaign is conducted and the functionality of the estimation method is verified on real data.

    Download full text (pdf)
    fulltext
  • 24.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    A note on the limitations of ZUPTs and the implications on sensor error modeling2012In: Proceeding of 2012 International Conference on Indoor Positioning and Indoor Navigation (IPIN), 13-15th November 2012, 2012Conference paper (Refereed)
    Abstract [en]

    The limitations of zero-velocity-updates (ZUPTs) for aiding a foot-mounted inertial navigation system (INS) are studied. Multiple significant modeling errors related to the ZUPTs are pointed out and quantified. Their implications for the possibility to estimate systematic inertial sensor errors are discussed and it is argued that modeling and estimating such errors, in foot-mounted ZUPT-aided INSs, should be avoided in many cases.

    Download full text (pdf)
    limits_of_zupts
  • 25.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Aligning the Forces-Eliminating the Misalignments in IMU Arrays2014In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 63, no 10, p. 2498-2500Article in journal (Refereed)
    Abstract [en]

    Ultralow-cost single-chip inertial measurement units (IMUs) combined into IMU arrays are opening up new possibilities for inertial sensing. However, to make these systems practical for researchers, a simple calibration procedure that aligns the sensitivity axes of the sensors in the array is needed. In this paper, we suggest a novel mechanical-rotation-rig-free calibration procedure based on blind system identification and a Platonic solid printable using a contemporary 3-D printer. The IMU array is placed inside the Platonic solid, and static measurements are taken with the solid subsequently placed on all sides. The recorded data are then used together with a maximum-likelihood-based approach to estimate the interIMU misalignment and the gain, bias, and sensitivity axis nonorthogonality of the accelerometers. The effectiveness of the method is demonstrated with calibration results from an in-house developed IMU array. MATLAB scripts for the parameter estimation and production files for the calibration device (solid) are provided.

  • 26.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    JOINT STATE AND MEASUREMENT TIME-DELAY ESTIMATION OF NONLINEARSTATE SPACE SYSTEMS2010In: Proc. ISSPA 2010, IEEE , 2010, p. 324-328Conference paper (Refereed)
    Abstract [en]

    Sensor fusion algorithms often assume perfect time synchronization of the sensor clocks. In a practical sensor-actuator setup this is often difficult to achieve which in turn can give rise to systematic errors in the sensor fusion. In this article we suggest how the effect of the synchronization error from an unknown static or slowly varying measurement time-delays in a nonlinear state space system can be handled by linearizing the measurement equation in time. Based on the linearization an augmented system is constructed from which the system states and the delays can be jointly estimated. Expressions for the system, measurement, and covariance matrices of the augmented system are derived. Finally, the feasibility of the suggested approach is demonstrated by an example and a Monte-Carlo simulation.

    Download full text (pdf)
    JOINT STATE AND MEASUREMENT TIME-DELAY ESTIMATION OF NONLINEAR STATE SPACE SYSTEMS
  • 27.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Performance characterisation of foot-mountedZUPT-aided INSs and other related systems2010In: Proc. IPIN2010, IEEE , 2010, p. 1-7Conference paper (Refereed)
    Abstract [en]

    Foot-mounted zero-velocity-update (ZUPT) aided inertial navigation system (INS) is a conceptually well known with publications in the area typically focusing on improved methods for filtering and addition of sensors and heuristics. Despite this, the performance characteristics, which would ultimately justify and give guidelines for such system modifications of ZUPT-aided INSs and other related systems, are in some aspects poorly documented. Unfortunately, the systems are non-linear, meaning that the performance is dependent on the system set-up, parameter setting, and the true trajectory. This complicates the process of evaluating performance and partially explains the few publications with detailed performance characterisation results. Therefore in this article we suggest and motivate methodologies for evaluating performance of ZUPT-aided INS and other related systems, we apply them to a suggested baseline set-up of the system, and study some aspects of the performance characteristics.

    Download full text (pdf)
    Performance characterisation of foot-mounted ZUPT-aided INSs and other related systems
  • 28.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Signal Processing.
    Hari, K.V.S.
    Department of ECE, Indian Institute of Science (IISc).
    Foot-mounted INS for Everybody: An Open-source Embedded Implementation2012In: 2012 IEEE/ION Position Location and Navigation Symposium (PLANS), IEEE , 2012, p. 140-145Conference paper (Refereed)
    Abstract [en]

    We present an open-source, realtime, embedded implementation of a foot-mounted, zero-velocity-update-aided inertial navigation system. The implementation includes both hardware design and software, uses off-the-shelf components and assembly methods, and features a standard USB interface. The software is written in C and can easily be modified to run user implemented a1gorithlUS. The hardware design and the software are released under permissive open-source licenses and production files, source code, documentation, and further resources areavailable at www.openshoe.org. The reproduction cost for a single unit is below $800, with the inertial measurement unit makingup the bulk ($700). The form factor of the implementation is small enough for it to be integrated in the sole of a shoe. A performance evaluation of the system shows a position errors for short trajectories «100 [m)) of ± 0.2-1 % of the traveled distance, depending on the shape of trajectory.

    Download full text (pdf)
    fulltext
  • 29.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zachariah, Dave
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Global Navigation Satellite Systems: An Enabler for In-Vehicle Navigation2012In: Handbook of Intelligent Vehicles / [ed] Azim Eskandarian, Springer London, 2012, p. 311-342Chapter in book (Other academic)
    Abstract [en]

    The emergence of global navigation satellite systems (GNSSs) has enabled tremendous development in vehicular navigation for various applications. The GNSS technology provides a unique global positioning capability with meter-level accuracy at a low hardware cost and zero marginal infrastructure cost. The GNSSs work by using the satellites as radio beacons, broadcasting a satellite-specific signal and their own position. The range to the satellites is measured up to a common clock offset, and any user equipped with a GNSS receiver capable of receiving the signal from four or more satellites can position itself by multilateration. The position, being a fundamental piece of information for automatizing and facilitating location-dependent system interaction and services, makes the GNSS an enabling technology for many intelligent vehicle and transportation system capabilities.

    This chapter will focus on introducing the basic principles of the GNSS technology and the signal processing that allows the GNSS receiver to determine its position: in>Sect. 1, the technology, its limitations, and currently available GNSSs are reviewed; in >Sect. 2, the principles of the GNSS positioning, the signal characteristics, and fundamental components are discussed; in>Sect. 3, the theoretical relations governing the positioning are presented; in>Sect. 4, implementation-related issues, error sources, and GNSS receivers are discussed; in>Sect. 5, the method of differential GNSS is introduced and current augmentation systems are reviewed; and finally in>Sect. 6, conclusions are drawn and references, for further reading about different aspects of the GNSS technology, are given.

  • 30.
    Nilsson, John-Olof
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zachariah, Dave
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Cooperative localization by dual foot-mounted inertial sensors and inter-agent ranging2013In: EURASIP Journal on Advances in Signal Processing, ISSN 1687-6172, E-ISSN 1687-6180, Vol. 164Article in journal (Refereed)
    Abstract [en]

    The implementation challenges of cooperative localization by dual foot-mounted inertial sensors and inter-agent ranging are discussed and work on the subject is reviewed. System architecture and sensor fusion are identified as key challenges. A partially decentralized system architecture based on step-wise inertial navigation and step-wise dead reckoning is presented. This architecture is argued to reduce the computational cost and required communication bandwidth by around two orders of magnitude while only giving negligible information loss in comparison with a naive centralized implementation. This makes a joint global state estimation feasible for up to a platoon-sized group of agents. Furthermore, robust and low-cost sensor fusion for the considered setup, based on state space transformation and marginalization, is presented. The transformation and marginalization are used to give the necessary flexibility for presented sampling based updates for the inter-agent ranging and ranging free fusion of the two feet of an individual agent. Finally, characteristics of the suggested implementation are demonstrated with simulations and a real-time system implementation.

    Download full text (pdf)
    fulltext
  • 31. Ohlsson, Martin
    et al.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Ohlsson, Jens
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Larm-anordning i fordon2011Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    An alarm method for vehicles comprises detection (S31) of whether a portable electronic apparatus (100) is connected to an alarm device (200) arranged in a vehicle (150), detection (S32) of whether a predetermined functionality is activated in the portable electronic apparatus (100), and activation (S33) of an alarm when the portable electronic apparatus (100) is unconnected or the predetermined functionality is inactivated.

  • 32.
    Panahandeh, Ghazaleh
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jansson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Calibration of the Accelerometer Triad of an Inertial Measurement Unit, Maximum Likelihood Estimation and Cramer-Rao Bound2010In: International Conference on Indoor Positioning and Indoor Navigation (IPIN), Zurich, September 15-17, 2010, IEEE , 2010, p. 1-6Conference paper (Refereed)
    Abstract [en]

    In this paper, a simple method to calibrate the accelerometer cluster of an inertial measurement unit (IMU) is proposed. The method does not rely on using a mechanical calibration platform that rotates the IMU into different precisely controlled orientations. Although the IMU is rotated into different orientations, these orientations do not need to be known. Assuming that the IMU is stationary at each orientation, the norm of the input is considered equal to the gravity acceleration. As the orientations of the IMU are unknown, the calibration of the accelerometer cluster is stated as a blind system identification problem where only the norm of the input to the system is known. Under the assumption that the sensor noises have a white Gaussian distribution the system identification problem is solved using the maximum likelihood estimation method. The accuracy of the proposed calibration method is compared with the Cram´er- Rao bound for the considered calibration problem.

    Download full text (pdf)
    fulltext
  • 33. Rantakokko, Jouni
    et al.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Eklöf, Fredrik
    Boberg, Bengt
    Junered, Marcus
    Akos, Dennis
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Bohlin, Hans
    Neregård, Fredrik
    Hoffmann, Franz
    Andersson, Daniel
    Jansson, Magnus
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Stenumgaard, Peter
    Positioning of emergency personnel in rescue operations: possibilities and vulnerabilities with existing techniques and identification of needs for future R&D2007Report (Other academic)
    Abstract [en]

    Summary and recommendations Presently, GPS-equipped mobile phones are launched at a large scale, enabling a variety of positioning based services. Indeed, GPS is expected to be the future killer application for mobile phones and services. The concept of accurate positioning by technical means implies a large number of applications not only for the mass market, but also for rescue services, fire brigades, police forces, and military and so on. For professional and governmental safety-of-life services the current systems are far from usable and large efforts have to be concentrated on research and development. Technologies based on GPS and other satellite-based positioning systems alone are vulnerable and are expected to malfunction in indoor or challenging electromagnetic environments, or due to antagonistic measures. Satellite-based positioning is a key component in a robust communication and positioning system aimed for first responders. Satellite based positioning in combination with local radio-based positioning systems and dead-reckoning or inertial navigation systems are enablers to fulfill the users? requirements on accuracy and availability of the positioning service. Sweden is a competent player within security. Around 300 companies with some 22.000 employees have been identified within the area. Swedish industry, research institutes and universities are expected to take part in international consortiums within EU FP7, as well as being a player within DHS funded research and development within the personal positioning and navigation area. The market potential for professional and safety-of-life personal equipment for robust positioning and communication with suitable means for information presentation is significant. In the US and the EU there are some 2 million incident responders each. On a national level we count some 35.000 fire fighters, police, and military personnel in international operations. A migration of the technology to private end-consumers as implemented in consumer electronics opens up a gigantic market for wireless services within navigation, gaming, and position-awareness services. Within the project positioning of first responders in rescue operations, robust positioning has been studied. From a system perspective, technologies for positioning of personnel are key system components within a platform for positioning, information transfer for command and control, and information processing and presentation for the personnel at all levels. \? Systems for training are needed to introduce the end-user to the technology, and for training and simulation of novel strategies enabled by the technology. Stationary training systems can be implemented with state-of-the art positioning methods. Feedback from the end-user to the R&D community is instrumental in the specification and development of future means for positioning of first responders. A research infrastructure, or test-bed, for implementation and evaluation of robust positioning is an essential tool. \? The functionality of the equipment has to be robust against hostile electromagnetic environments, either due to the actual physical environment (indoor scenario, intersystem interference from nearby electronic equipment, scenario within a large steel constructions, or power plant, etc), or due to electronic warfare antagonistic actions. Research has to be performed in several areas such as channel characterization for radio positioning, quality of satellite signals subjected to interference, and integrity of sensor information due to external influences. \? Contemporary MEMS-technology provides small-size sensors with low energy consumption. The rapid development within sensor technologies enables data fusion from a plurality of sensors by digital signal processing. Fundamental issues within digital signal processing have to be studied in several fields, including methods to enhance sensor performance by incorporating behavioral modeling; fusion of digital information from a plurality of sensors; aspects of hardware implementation to fulfill requirements on size, weight and uptime, and software defined receivers for radio-based positioning, communication and mapping. In summary, future systems for positioning of first responders in rescue operations rely on the development of infra-structure aimed for end-users in a training scenario; and a platform for R&D-purposes. In parallel, fundamental issues have to be studied regarding the electromagnetic environment, as well as methodologies in digital signal processing.

  • 34. Rantakokko, Jouni
    et al.
    Rydell, Joakim
    Fors, Karina
    Linder, Sara
    Wirkander, Sven-Lennart
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Technologies for first responder indoor localization2009Conference paper (Refereed)
  • 35.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    GNSS-aided INS for land vehicle positioning and navigation2007Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis begins with a survey of current state-of-the art in-car navigation systems. The pros and cons of the four commonly used information sources — GNSS/RF-based positioning, vehicle motion sensors, vehicle models and map information — are described. Common filters to combine the information from the various sources are discussed.

    Next, a GNSS-aided inertial navigation platform is presented, into which further sensors such as a camera and wheel-speed encoder can be incorporated. The construction of the hardware platform, together with an extended Kalman filter for a closed-loop integration between the GNSS receiver and the inertial navigation system (INS), is described. Results from a field test are presented.

    Thereafter, an approach is studied for calibrating a low-cost inertial measurement unit (IMU), requiring no mechanical platform for the accelerometer calibration and only a simple rotating table for the gyro calibration. The performance of the calibration algorithm is compared with the Cramér-Rao bound for cases where a mechanical platform is used to rotate the IMU into different precisely controlled orientations.

    Finally, the effects of time synchronization errors in a GNSS-aided INS are studied in terms of the increased error covariance of the state vector. Expressions for evaluating the error covariance of the navigation state vector are derived. Two different cases are studied in some detail. The first considers a navigation system in which the timing error is not taken into account by the integration filter. This leads to a system with an increased error covariance and a bias in the estimated forward acceleration. In the second case, a parameterization of the timing error is included as part of the estimation problem in the data integration. The estimated timing error is fed back to control an adjustable fractional delay filter, synchronizing the IMU and GNSS-receiver data.

    Download full text (pdf)
    FULLTEXT01
  • 36.
    Skog, Isaac
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Low-Cost Navigation Systems: A Study of Four Problems2009Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Today the area of high-cost and high-performance navigation for vehicles is a well-developed field. The challenge now is to develop high-performance navigation systems using low-cost sensortechnology. This development involves problems spanning from signal processing of the dirty measurements produced by low-costsensors via fusion and synchronization of information produced by a large set of diverse sensors, to reducing the size and energyconsumption of the systems. This thesis examines and proposessolutions to four of these problems.

    The first problem examined is the time synchronizing of the sensordata in a global positioning system aided inertial navigationsystem in which no hardware clock synchronization is possible. A poor time synchronization results in an increased mean squareerror of the navigation solution and expressions for calculating this mean square error are presented. A method to solve the timesynchronization issue in the data integration software is proposed. The potential of the method is illustrated with tests onreal-world data that are subjected to timing errors.

    The second problem examined is the achievable clocksynchronization accuracy in a sensor network employing a two-waymessage exchange model. The Cramer-Rao bound for the estimation of the clock parameters is derived and transformed in to a lower bound on the mean square error of the clock offset.Further, an approximate maximum likelihood estimator for the clockparameters is proposed. The estimator is shown to be of low complexity and to have a mean square error in the vicinity of the Cramer-Rao bound.

    The third problem examined is the detection of the time epochswhen zero-velocity updates can be applied in a foot-mountedpedestrian navigation system. Four general likelihood ratio testsfor detecting when the navigation system is stationary based onthe inertial measurement data are studied. The performance of thefour detectors is evaluated using levelled ground, forward-gaitdata. The results show that the signals from the gyroscopes holdthe most reliable information for the zero-velocity detection.

    The fourth problem examined is the calibration of a low-costinertial measurement unit. A calibration procedure that relaxesthe accuracy requirements of the orientation angles the inertialmeasurement unit must be placed in during the calibration isstudied. The proposed calibration method is compared with theCramer-Rao bound for the case when the inertial measurementunit is rotated into precisely controlled orientations. Simulationresults show that the mean square error of the estimated sensormodel parameters reaches the Cramer-Rao bound within fewdecibels. Thus, the proposed method may be acceptable for a widerange of low-cost applications.

    Download full text (pdf)
    FULLTEXT01
  • 37.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Almquist, Gustav
    Andersson, Stefan
    Petkov, Petko
    Voice over IP application on TMS320C6701 EVM DSP Board2004Conference paper (Refereed)
    Abstract [en]

    Development of a low bit-rate voice over IP application is described. A speech coding algorithm is constructed and implemented on a digital signal processor (DSP). The algorithm is based on a sub-band mixed excitation LPC vocoder structure and operates at a rate of 2000 bits per second. Implementation is done on two TMS320C6701 floating point DSP’s each connected to a PC. On the PC, a graphical user interface (GUI) controls the data flow over the IP network. The application runs in full duplex and supports poor to fair sound quality depending on the used recording equipment.

    Download full text (pdf)
    fulltext
  • 38.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    A low-cost GPS aided inertial navigation system for vehicle applications2005Conference paper (Refereed)
    Abstract [en]

    In this paper an approach for integration between GPS and inertial navigation systems (INS) is described. The continuous-time navigation and error equations for an earth-centered earth-fixed INS system are presented. Using zero order hold sampling, the set of equations is discretized. An extended Kalman filter for closed loop integration between the GPS and INS is derived. The filter propagates and estimates the error states, which are fed back to the INS for correction of the internal navigation states. The integration algorithm is implemented on a host PC, which receives the GPS and inertial measurements via the serial port from a tailor made hardware platform, which is briefly discussed. Using a battery operated PC the system is fully mobile and suitable for real-time vehicle navigation. Simulation results of the system are presented.

  • 39.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Calibration of a MEMS inertial measurement unit2006In: Proc. XVII IMEKO World Congress, (Rio de Janeiro, Brazil), Sept.2006, 2006Conference paper (Refereed)
    Abstract [en]

    An approach for calibrating a low-cost IMU isstudied, requiring no mechanical platform for the accelerometercalibration and only a simple rotating table for the gyrocalibration. The proposed calibration methods utilize the factthat ideally the norm of the measured output of the accelerometerand gyro cluster are equal to the magnitude of appliedforce and rotational velocity, respectively. This fact, togetherwith model of the sensors is used to construct a cost function,which is minimized with respect to the unknown model parametersusing Newton’s method. The performance of the calibrationalgorithm is compared with the Cram´er-Rao bound forthe case when a mechanical platform is used to rotate the IMUinto different precisely controlled orientations. Simulation resultsshows that the mean square error of the estimated sensormodel parameters reaches the Cram´er-Rao bound within8 dB, and thus the proposed method may be acceptable for awide range of low-cost applications.

  • 40.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Effects of time synchronization errors in GNSS-aided INS2008In: 2008 IEEE/ION POSITION, LOCATION AND NAVIGATION SYMPOSIUM, VOLS 1-3, NEW YORK: IEEE , 2008, p. 370-376Conference paper (Refereed)
    Abstract [en]

    The effects of time synchronization errors in a GNSS-aided inertial navigation system (INS) are studied in terms of the increased error covariance of the state vector. Expressions for evaluating the error covariance of the navigation state vector-given the vehicle trajectory and the model of the INS error dynamics-are derived. Two different cases are studied in some detail. The first case considers a navigation system in which the timing error is not included in the integration filter. This leads to a system with an increased error covariance and a bias in the estimated forward acceleration. In the second case, a parameterization of the timing error is included as a part of the estimation problem in the data integration. Simulation results show that by including the timing error in the estimation problem, almost perfect time synchronization is obtained and the bias in the forward acceleration is removed.

  • 41.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    In-car navigation basics2012In: Handbook of Intelligent Vehicles / [ed] Eskandarian, Azim (Ed.), Springer Publishing Company, 2012Chapter in book (Other academic)
  • 42.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    In-Car Positioning and Navigation Technologies: a survey2009In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 10, no 1, p. 4-21Article, review/survey (Refereed)
    Abstract [en]

    In-car positioning and navigation has been a killer application for Global Positioning System (GPS) receivers, and a variety of electronics for consumers and professionals have been launched on a large scale. Positioning technologies based on stand-alone GPS receivers are vulnerable and, thus, have to be supported by additional information sources to obtain the desired accuracy, integrity, availability, and continuity of service. A survey of the information sources and information fusion technologies used in current in-car navigation systems is presented. The pros and cons of the four commonly used information sources, namely, 1) receivers for radio-based positioning using satellites, 2) vehicle motion sensors, 3) vehicle models, and 4) digital map information, are described. Common filters to combine the information from the various sources are discussed. The expansion of the number of satellites and the number of satellite systems, with their usage of available radio spectrum, is an enabler for further development, in combination with the rapid development of microelectromechanical inertial sensors and refined digital maps.

  • 43.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Indirect Instantaneous Car-Fuel Consumption Measurements2014In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 63, no 12, p. 3190-3198Article in journal (Refereed)
    Abstract [en]

    A method to estimate the instantaneous fuel consumption of a personal car, using speed and height data recorded by a global positioning system receiver and vehicle parameters accessible via national vehicle registers and databases on the world wide web, is proposed. The method is based upon a physical model describing the relationship between the dynamics of the car, engine speed, and energy consumption of the system. An evaluation of the proposed method is done by comparing the estimated instantaneous fuel consumption with that measured by the car's onboard diagnostics data bus. The results of three tests with different cars driven in mixed highway and urban conditions indicate that the instantaneous fuel consumption may be estimated with a root mean square error of similar to 0.3 [g/s], in terms of a normalized mean square error, that corresponded to slightly <10%. One application of the proposed method is in the development of smartphone applications that educate drivers to drive more fuel efficiently.

  • 44.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Händel, Peter
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    State-of-the-art in-car navigation: An overview2012In: Handbook of Intelligent Vehicles, Springer London , 2012, Vol. 1-2, p. 436-462Chapter in book (Other academic)
    Abstract [en]

    The basics around in-car navigation is discussed, including the principals of contemporary systems, global navigation satellite system basics, dead-reckoning, mapmatching, and strategies for information fusion. In-car navigation system are generally made out of three building blocks, an information source block, an information fusion block, and an user interface block. This chapter presents an overview of the information source block and the information fusion block. First, the ideas of operation and main characteristics of the four most commonly used information sources, global navigation satellite systems, vehicle motion sensors, road maps, and mathematical models of the vehicle dynamics, are reviewed. Thereafter, common techniques to combine the information from the different information sources into an estimate of the position, velocity, etc. of the car are reviewed.

  • 45.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Synchronization by Two-Way Message Exchanges: Cramer-Rao Bounds, Approximate Maximum Likelihood, and Offshore Submarine Positioning2010In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 58, no 4, p. 2351-2362Article in journal (Refereed)
    Abstract [en]

    Accurate clock synchronization is vital to many applications of wireless sensor networks (WSNs). The availability of a mathematical tool that at an early design stage can provide insight into the theoretically achievable performance of the clock synchronization may accordingly be valuable in the initial design phase of the network. Therefore, the achievable clock synchronization accuracy is examined in a WSN employing a two-way message exchange model under a Gaussian assumption. The Cramer-Rao bound for the estimation of the clock parameters is derived for four different parameterizations (i. e., different nuisance parameters), reflecting different levels of prior knowledge concerning the system parameters. The results on the Cramer-Rao bound are transformed into a lower bound on the mean square error of the clock offset, a figure of merit often more relevant, characterizing the system performance. Further, by introducing a set of artificial observations through a linear combination of the observations originally obtained in the two-way message exchange, an approximate maximum likelihood estimator for the clock parameters is proposed. The estimator is shown to be of low complexity and it obeys near-optimal performance, that is, a mean square error in the vicinity of the Cramer-Rao bound. The applicability of the derived results is shown through a simulation study of an offshore engineering scenario, where a remotely operated underwater vehicle is used for operations at the seabed. The position of the vehicle is tracked using a WSN.

  • 46.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Time Synchronization Errors in Loosely Coupled GPS-Aided Inertial Navigation Systems2011In: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 12, no 4, p. 1014-1023Article in journal (Refereed)
    Abstract [en]

    The effects of data time synchronization errors in a loosely coupled Global-Positioning-System (GPS)-aided inertial navigation system (INS) are studied and quantified in terms of the increased mean square error (MSE) of the navigation solution. An expression for evaluating the MSE of the navigation solution, given the vehicle trajectory and the model of the INS error dynamics, is derived. Thereafter, a software-based time synchronization method, where the time synchronization error is included as a state to be estimated by the data integration filter, is proposed. A practical approach to the implementation of the proposed time synchronization method is also briefly described. Moreover, an expression for the MSE of the navigation solution in the system that employs the proposed synchronization method is derived. Finally, through simulations and tests with real-world data, the correctness of the derived MSE expressions is validated, and the application of the proposed synchronization method is shown. The test results show that, with the proposed synchronization approach, a data time synchronization, which is accurate to the order of a few milliseconds, can be achieved.

  • 47.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nilsson, John-Olof
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Rantakokko, Jouni
    Zero-Velocity Detection-An Algorithm Evaluation2010In: IEEE Transactions on Biomedical Engineering, ISSN 0018-9294, E-ISSN 1558-2531, Vol. 57, no 11, p. 2657-2666Article in journal (Refereed)
    Abstract [en]

    In this paper, we investigate the problem of detecting-time epochs when zero-velocity updates can be applied in a foot-mounted inertial navigation (motion-tracking) system. We examine three commonly used detectors: the acceleration-moving variance detector, the acceleration-magnitude detector, and the angular rate energy detector. We demonstrate that all detectors can be derived within the same general likelihood ratio test (LRT) framework, given the different prior knowledge about the sensor signals. Further, by combining all prior knowledge, we derive a new LRT detector. Subsequently, we develop a methodology to evaluate the performance of the detectors. Employing the developed methodology, we evaluate the performance of the detectors using leveled ground, slow (approximately 3 km/h) and normal (approximately 5 km/h) gait data. The test results are presented in terms of detection versus false-alarm probability. Our preliminary results show that the new detector performs marginally better than the angular rate energy detector that outperforms both the acceleration-moving variance detector and the acceleration-magnitude detector.

  • 48.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ohlsson, Martin
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Ohlsson, Jens
    Challenges in smartphone-driven usage based insurance2013In: 2013 IEEE Global Conference on Signal and Information Processing, GlobalSIP 2013 - Proceedings, IEEE conference proceedings, 2013, p. 1135-1135Conference paper (Refereed)
    Abstract [en]

    Usage Based Insurance (UBI) programs for car insurance is becoming mainstream using tailored vehicle mounted hardware, where the commercial initiatives can be traced back to the mid-nineties [1]. The smartphone has been identified as an enabler for future UBI, replacing the vehicle (after-) mounted dedicated hardware with a ubiquitous device with a plurality of sensors, means for data processing and wireless communication. This presentation addresses some signal processing challenges in smartphone-driven UBI.

  • 49.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Information Science and Engineering.
    Karagiannis, Ioannis
    KTH, School of Electrical Engineering (EES).
    Bergsten, Anders Betts
    Harden, Jonas
    Gustafsson, Lars
    Handel, Peter
    A Smart Sensor Node for the Internet-of-Elevators-Non-Invasive Condition and Fault Monitoring2017In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 17, no 16, p. 5198-5208Article in journal (Refereed)
    Abstract [en]

    The signal processing scheme of a smart sensor node for the Internet-of-Elevators is presented. The sensor node is a self-contained black box unit only requiring power to be supplied, which enables a cost efficient way to modernize existing elevator systems in terms of condition monitoring capabilities. The sensor node monitors the position of the elevator using an inertial navigation system in conjugation with a simultaneous localization and mapping framework. Features reflecting the elevator system's operation and health condition are calculated by evaluating the ride quality parameters defined by the ISO 18738-1 standards, the vibration versus frequency spectrum, and the vibration versus position spectrum. Abnormal stops are identified by detecting decelerations that deviate from the typical deceleration pattern of the elevator or when the stopping position of the elevator does not match the learned floor levels. Furthermore, the condition of the door system is monitored by tracking the magnetic field variations that the motion of the doors creates; the number of door openings and the time required for the doors to close are estimated. The capability and performance of the blacksignal processing scheme are illustrated through a series of experiments. The experiments show, inter alia, that using low-cost sensors similar to those in a smartphone, the position of the elevator car can, with 99.9% probability, be estimated with an error of less than 1 m for travels up to 43 s long. The experiments also indicate that small degradations in the doors' closing time can be detected from the magnetic field measurements.

  • 50.
    Skog, Isaac
    et al.
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Nilsson, John Olof
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Händel, Peter
    KTH, School of Electrical Engineering (EES), Signal Processing. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    An open-source multi inertial measurement unit (MIMU) platform2014In: 1st IEEE International Symposium on Inertial Sensors and Systems, ISISS 2014 - Proceedings, IEEE Computer Society, 2014Conference paper (Refereed)
    Abstract [en]

    An open-source low-cost multi inertial measurement unit (MIMU) systems platform is presented. First, the layout and system architecture of the platform, as well as the novel communication interface used to simultaneously communicate with the 18 IMUs in the platform are described. Thereafter, the potential gains of using a MIMU system are described and discussed. Finally, the error characteristics of the platform, when stationary, are illustrated using Allan variance plots.

12 1 - 50 of 69
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf