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)

Abstract Designing energy-efficient multiprocessing hardware for applications such as video decoding or MIMO-OFDM baseband processing is challenging because these applications require high throughput, as well as flexibility for efficient use of the processing resources. Application specific hardwired accelerator circuits are the most energy-efficient processing resources, but are inflexible by nature. Furthermore, designing an application specific circuit is expensive and time-consuming. A solution that maintains the energy-efficiency of accelerator circuits, but makes them flexible as well, is to make the accelerator circuits fine-grained. Fine-grained application specific processing elements can be designed to implement general purpose functions that can be used in several applications and their small size makes the design and verification times reasonable. This thesis proposes an efficient method for orchestrating the use of heterogeneous fine-grained processing elements in dynamic applications without introducing tremendous orchestration overheads. Furthermore, the thesis presents a processing element management unit which performs scheduling and independent dispatching, and works with such low overheads that the use of low latency processing elements becomes worthwhile and efficient. Dynamic orchestration of processing elements requires run-time scheduling that has to be done very fast and with as few resources as possible, for which this work proposes dividing the application into short static parts, whose schedules can be determined at system design time. This approach, often called quasi-static scheduling, captures the dynamic nature of the application, as well as minimizes the computations of run-time scheduling. Enabling low overhead quasi-static scheduling required studying simultaneously the computational complexity and performance of simple but efficient scheduling algorithms. The requirements lead to the use of flow-shop scheduling. This thesis is the first work that adapts the flow-shop scheduling algorithms to different multiprocessor memory architectures. An extension to the flow-shop model is also presented, which enables modeling a wider scope of applications than traditional flow-shop. The feasibility of the proposed approach is demonstrated with a real multiprocessor solution that is instantiated on a field-programmable gate array.

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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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With the increased capacity of the Internet it is possible to use it for real-time multimedia applications, such as video conferences. There is also an increasing interest in using Internet technology in cellular networks, such as mobile phones. However, the link characteristics for a wireless network are very different from the characteristics of a wired network, which the Internet originally was designed for. The main difference is the time varying link characteristics of the wireless link channel. The variation are due to multipath fading and interference. Herein it is investigated how the wireless link can cooperate with the source coder and network transportation to increase the end-to-end quality, without increasing the delay. Under the assumption that the wireless link is the most likely bottleneck of the system. It is shown that by using a progressive source coder and extending the Internet protocols to enable quick rate adaption by routers and wireless links it is possible to increase the end-to-end quality. / Godkänd; 2003; 20070215 (ysko)

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The estimation of frequencies and corresponding harmonic overtones is a problem of great importance in many situations. Applications can, for example, be found in supervision of electrical power transmission lines, in seismology and in acoustics. Generally, a periodic function with an unknown fundamental frequency in cascade with a parameterized and unknown nonlinear function can be used as a signal model for an arbitrary periodic signal. The main objective of the proposed modeling technique is to estimate the fundamental frequency of the periodic function in addition to the parameters of the nonlinear function. The thesis is divided into four parts. In the first part, a general introduction to the harmonic signal modeling problem and different approaches to solve the problem are given. Also, an outline of the thesis and future research topics are introduced. In the second part, a previously suggested recursive prediction error method (RPEM) for harmonic signal modeling is studied by numerical examples to explore the ability of the algorithm to converge to the true parameter vector. Also, the algorithm is modified to increase its ability to track the fundamental frequency variations. A modified algorithm is introduced in the third part to give the algorithm of the second part a more stable performance. The modifications in the RPEM are obtained by introducing an interval in the nonlinear block with fixed static gain. The modifications that result in the convergence analysis are, however, substantial and allows a complete treatment of the local convergence properties of the algorithm. Moreover, the Cramér–Rao bound (CRB) is derived for the modified algorithm and numerical simulations indicate that the method gives good results especially for moderate signal to noise ratios (SNR). In the fourth part, the idea is to give the algorithm of the third part the ability to estimate the driving frequency and the parameters of the nonlinear output function parameterized also in a number of adaptively estimated grid points. Allowing the algorithm to automatically adapt the grid points as well as the parameters of the nonlinear block, reduces the modeling errors and gives the algorithm more freedom to choose the suitable grid points. Numerical simulations indicate that the algorithm converges to the true parameter vector and gives better performance than the fixed grid point technique. Also, the CRB is derived for the adaptive grid point technique.

In many applications such as heat diffusion and flow problems, it is of interest to describe the process behavior inside a particular medium. An example can be the strive for estimating certain parameters related to the material. These processes are often modeled by a partial differential equation. Certain methods for identifying unknown material constants require the model to be of finite order. This thesis describes how the diffusion process can be approximated with finite order model, and how the accuracy of an estimated model depends on the model order. In particular, a detailed analysis is carried out for the case when the approximate model accounts for solving the diffusion by a difference method.