Before using a parametric model one has to be sure that it offers a reasonable description of the system to be modeled. If a bad model structure is employed, the obtained model will also be bad, no matter how good is the parameter estimation method. There exist many possible ways of validating candidate models. This thesis focuses on one of the most common ways, i.e., the use of information criteria. First, some common information criteria are presented, and in the later chapters, various extentions and implementations are shown. An important extention, which is advocated in the thesis, is the multi-model (or model averaging) approach to model selection. This multi-model approach consists of forming a weighted sum of several candidate models, which then can be used for inference.

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This thesis focuses on the possibility of using ultrasonic measurement techniques for energy gas characterization. The idea is to combine both on-line flow measurements with non-invasive fluid characterization in the same measurement setup using the same sensor(s). The long-term goal of the project is to develop measurement methods based on ultrasonic techniques that can measure; the flow rate, the energy content, detect impurities, and estimate the composition. In this thesis different problems concerning gas characterization and modeling are addressed. The information obtained from ultrasonic measurements are limited to spectral variations in the attenuation and phase velocity. Hence, part of the research is focused on estimating these quantities accurately with low uncertainty. Another area is parametric modeling and identification of the bulk modulus, where a new model structure for gas mixtures with complex dynamic behavior and/or unknown components is presented, capable of handling the combined effect of the absorption mechanisms. Finally, the problem of estimating the composition of a gas mixture is considered. The results show that it is possible to estimate the composition of processed and upgraded biogas, with high accuracy and precision, by combining the developed estimation techniques with multiple linear regression methods. The thesis consists of two parts. The first part includes an introduction to the research area together with a short summary of the contributions. The second part contains a collection of four papers describing the research. / <p>Godkänd; 2006; 20061115 (ysko)</p>

With an increased demand on productivity and safety in industry, new issues in terms of automated material handling arise. This results in industries not having a homogenous fleet of trucks and driven and driverless trucks are mixed in a dynamic environment. Driven trucks are more flexible than driverless trucks, but are also involved in more accidents. A transition from driven to driverless trucks can increase safety, but also productivity in terms of fewer accidents and more accurate delivery. Hence, reliable and standardized solutions that avoid accidents are important to achieve high productivity and safety. There are two different safety standards for driverless trucks for Europe (EN1525) and U.S. (B56.5–2012) and they have developed differently. In terms of obstacles, they both consider contact with humans. However, a machinery-shaped object has recently been added to the U.S. standard (B56.5–2012). The U.S. standard also considers different materials for different sensors and non-contact sensors. For obstacle detection, the historical contact-sensitive mechanical bumpers as well as the traditional laser scanner used today both have limitations – they do not detect hanging objects. In this work we have identified several thin objects that are of interest in an industrial environment. A test apparatus with a thin structure is introduced for a more uniform way to evaluate sensors. To detect thin obstacles, we used a standard setup of a stereo system and developed this further to a trinocular system (a stereo system with three cameras). We also propose a method to evaluate 3D sensors based on the information from a 2D range sensor. The 3D model is created by measuring the position of a reflector with known position to an object with a known size. The trinocular system, a 3D TOF camera and a Kinect sensor are evaluated with this method. The results showed that the method can be used to evaluate sensors. It also showed that 3D sensor systems have potential to be used on driverless trucks to detect obstacles, initially as a complement to existing safety classed sensors. To improve safety and productivity, there is a need for harmonization of the European and the U.S. safety standards. Furthermore, parallel development of sensor systems and standards is needed to make use of state-of-the-art technology for sensors.

Aspects of modern communication systems is the overall theme of this thesis with emphasis placed on multicarrier modulation. The work considers four facets of such systems; namely duplexing design, interference mitigation, channel estimation and multiuser detection. The first area deals with duplexing design for very high bit rate digital subscriber lines (VDSL) using discrete multitone modulation (DMT). We present a novel method based on DMT - the Zipper duplex method. Zipper is proposed for VDSL in different standardization bodies worldwide - International (ITU), North America (ANSI) and in Europe (ETSI) where it also has been accepted as a part of the VDSL standard. Zipper has superior flexibility and spectrum efficiency. This is obtained by freely assigning different subcarriers for the up- and downstream direction. In one design Zipper operates fully network synchronized by using a masterclock. In an asynchronous design Zipper operates without any reference to a masterclock which is a requirement for unbundled networks but reduces some of the flexibility. To obtain highest flexibility in unbundled networks, without using a masterclock, an algorithm is derived that self-synchronizes all Zipper modems. Another area deals with interference- and distortion mitigation. Narrowband interference (NBI) in orthogonal frequency division multiplexing- (OFDM) and DMT-based systems is considered. NBI can be very harmful for both radio- and wireline systems. We introduce two efficient NBI cancellers for OFDM and DMT. One canceller is based on a deterministic polynomial model of the NBI. The other canceller models it as a narrowband stochastic process and use the linear minimum mean square error (LMMSE) criterion for the cancellation. We lower its complexity by using the theory of optimal rank reduction. Impulse noise is a different type of harmful interference that can be encountered in VDSL. In this thesis we study the effects of impulse noise in DMT-based VDSL systems and present a robust generalized likelihood ratio test for detecting impulse noise. It is used for obtaining reliable erasures in a Reed-Solomon decoding scheme which reduces the probability of symbol errors significantly. Pilot symbol assisted modulation (PSAM) can be used in OFDM for tracking the distortion variations in a fading radio channel. We analyze the pilot symbol spacing in PSAM as a trade-off between high effective SNR and good channel tracking capabilities for two channel estimators with different complexities. Code division multiple access (CDMA) is part of the standard for the third generation of mobile phones. In this thesis we present a low complexity multiuser detector for a wireless DS-CDMA system. With a pipelined structure it can produce maximum likelihood sequence detector (MLSD) decisions on many of the received bits by only performing additions after the front end matched filters. / Godkänd; 2001; 20061113 (haneit)

This thesis consists of an introduction and five parts dealing with digital communication. Three parts address Discrete Multi-Tone modulation (DMT), a wireline form of Orthogonal Frequency Division Multiplexing (OFDM). One part addresses channel estimation in wireless OFDM and one addresses multiuser detection in wireless Direct Sequence-Code Division Multiple Access (DS- CDMA).The first part presents a new duplex method, called Zipper, for Very High bit rate Digital Subscriber Lines (VDSL). It is a duplex method that offer high flexibility and compatibility with existing services in the access network. The second part presents a digital Radio Frequency Interference (RFI) suppression method. It is located in the frequency domain and it can be used by any DMT-based VDSL system. The third part presents a method to run Zipper in an asynchronous mode with only a small performance loss. This can be of interest for telecom operators when constructing a VDSL system. The fourth part examines the trade-off between pilot symbol spacing and symbol error rate in a wireless OFDM system using Pilot Symbol Assisted Modulation (PSAM). The last part presents a low complexity multiuser detector for wireless DS-CDMA. It consists of a pipelined detector structure that produces Maximum Likelihood Secence Detector (MLSD) decisions on some of the received bits in the sequence. The remaining, previously undetected bits, are fed to a secondary post-processor. / Godkänd; 1999; 20070404 (ysko)

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Many industries are dealing with composite materials and multi-layered structures of various materials. Errors in the manufacturing process may lead to defects in the final product, and hence, avoiding imperfections is crucial. The importance of repeated quality assurance online is therefore essential during the process. For quality assurance the industry needs accurate and cost-effective diagnostic methods. Ultrasonic measurement techniques are familiar to most people from their medical applications, such as looking for the fetus in the mother's womb or imaging tissue anomalies in order to detect e.g. tumours. However, applications for ultrasound are widely used in the industry today, as a nondestructive evaluation technique for many different media. In the aircraft industry for example, components are inspected before they are assembled into the aircraft and also periodically inspected throughout their useful life, by using for example ultrasonic techniques. Ultrasonic inspection is extensively used to locate tiny cracks and to measure the thickness of the aircraft skin from the outside. The objectives of this thesis is to address the advancement of methods for ultrasonic characterization of layered media. The research problem addressed is stated as: How can methods for Nondestructive Evaluation of layered media using ultrasound be developed or improved? To easier approach this question it can be divided into smaller parts which are addressed separately and in combinations. The approach to answer the research question and the project objectives is chosen to be in the field of ultrasound, because of its superior penetrating properties in solid materials. When using ultrasound and ultrasonic measurement techniques we are restricted to measure frequency dependent phase velocity and attenuation. However, these properties can be used to calculate material properties of interest in the investigated medium. The focus of the work in this thesis is on the development of a parametric model for multi-layered materials. The model is used to describe ultrasonic signals reflected from a multi-layered structure in a successive way. Results show that the proposed model can be used to deal with the research problem in this thesis. The thesis is divided into two parts. The first part contains an introduction to the research area together with a summary of thecontributions, and the second part is a collection of four papers describing the research. / <p>Godkänd; 2007; 20070528 (ysko)</p>

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