Latest Ph.D. Theseshttp://theses.eurasip.org/feeds/rss/theses/Most recent submissions to EURASIP's Library of Ph.D. Theses.en-usCopyright (c) 2018 EURASIPFri, 09 Mar 2018 22:47:34 +0200Robust Algorithms for Linear and Nonlinear Regression via Sparse Modeling Methods: Theory, Algorithms and Applications to Image Denoisinghttp://theses.eurasip.org/theses/770/robust-algorithms-for-linear-and-nonlinear/The task of robust regression is of particular importance in signal processing, statistics and machine learning. Ordinary estimators, such as the Least Squares (LS) one, fail to achieve sufficiently good performance in the presence of outliers. Although the problem has been addressed many decades ago and several methods have been established, it has recently attracted more attention in the context of sparse modeling and sparse optimization techniques. The latter is the line that has been followed in the current dissertation. The reported research, led to the development of a novel approach in the context of greedy algorithms. The model adopts the decomposition of the noise into two parts: a) the inlier noise and b) the outliers, which are explicitly modeled by employing sparse modeling arguments. Based on this rationale and inspired by the popular Orthogonal Matching Pursuit (OMP), two novel ...Papageorgiou, GeorgeFri, 09 Mar 2018 22:47:34 +0200http://theses.eurasip.org/theses/770/robust-algorithms-for-linear-and-nonlinear/Behavioral Modeling and Digital Predistortion of Radio Frequency Power Amplifiershttp://theses.eurasip.org/theses/769/behavioral-modeling-and-digital-predistortion-of/The radio frequency power amplifier (RF-PA) within a digital wireless transmitter is a critical component regarding both the energy consumption and the signal quality. Especially due to today's broadband multicarrier modulation methods that generate signals with high peak-to-average power ratio, it is very hard to construct RF-PAs that achieve good energy efficiency and fulfill the strict linearity requirements imposed by the standard. Because of this, the digital predistortion (DPD) of RF-PAs has become a key technique for implementing energy efficient, high data rate wireless transmitters. This thesis investigates theoretical foundations and practical methods for the behavioral modeling and DPD of RF-PAs. The main contributions are a semi-physical model of the joint linearity-efficiency characteristics of RF-PAs, a detailed analysis of polynomial baseband models of RF-PAs focusing on the often neglected even-order terms in baseband, and a collection of practical methods for ...Enzinger, HaraldThu, 08 Mar 2018 15:50:35 +0200http://theses.eurasip.org/theses/769/behavioral-modeling-and-digital-predistortion-of/Good Features to Correlate for Visual Trackinghttp://theses.eurasip.org/theses/768/good-features-to-correlate-for-visual-tracking/Estimating object motion is one of the key components of video processing and the first step in applications which require video representation. Visual object tracking is one way of extracting this component, and it is one of the major problems in the field of computer vision. Numerous discriminative and generative machine learning approaches have been employed to solve this problem. Recently, correlation filter based (CFB) approaches have been popular due to their computational efficiency and notable performances on benchmark datasets. The ultimate goal of CFB approaches is to find a filter (i.e., template) which can produce high correlation outputs around the actual object location and low correlation outputs around the locations that are far from the object. Nevertheless, CFB visual tracking methods suffer from many challenges, such as occlusion, abrupt appearance changes, fast motion and object deformation. The main reasons ...Gundogdu, ErhanTue, 06 Mar 2018 22:52:29 +0200http://theses.eurasip.org/theses/768/good-features-to-correlate-for-visual-tracking/Polynomial Matrix Eigenvalue Decomposition Techniques for Multichannel Signal Processinghttp://theses.eurasip.org/theses/767/polynomial-matrix-eigenvalue-decomposition/Polynomial eigenvalue decomposition (PEVD) is an extension of the eigenvalue decomposition (EVD) for para-Hermitian polynomial matrices, and it has been shown to be a powerful tool for broadband extensions of narrowband signal processing problems. In the context of broadband sensor arrays, the PEVD allows the para-Hermitian matrix that results from the calculation of a space-time covariance matrix of the convolutively mixed signals to be diagonalised. Once the matrix is diagonalised, not only can the correlation between different sensor signals be removed but the signal and noise subspaces can also be identified. This process is referred to as broadband subspace decomposition, and it plays a very important role in many areas that require signal separation techniques for multichannel convolutive mixtures, such as speech recognition, radar clutter suppression, underwater acoustics, etc. The multiple shift second order sequential best rotation (MS-SBR2) algorithm, built ...Wang, ZeliangMon, 05 Mar 2018 14:33:03 +0200http://theses.eurasip.org/theses/767/polynomial-matrix-eigenvalue-decomposition/Feedback Delay Networks in Artificial Reverberation and Reverberation Enhancementhttp://theses.eurasip.org/theses/766/feedback-delay-networks-in-artificial/In today's audio production and reproduction as well as in music performance practices it has become common practice to alter reverberation artificially through electronics or electro-acoustics. For music productions, radio plays, and movie soundtracks, the sound is often captured in small studio spaces with little to no reverberation to save real estate and to ensure a controlled environment such that the artistically intended spatial impression can be added during post-production. Spatial sound reproduction systems require flexible adjustment of artificial reverberation to the diffuse sound portion to help the reconstruction of the spatial impression. Many modern performance spaces are multi-purpose, and the reverberation needs to be adjustable to the desired performance style. Employing electro-acoustic feedback, also known as Reverberation Enhancement Systems (RESs), it is possible to extend the physical to the desired reverberation. These examples demonstrate a wide range of applications ...Schlecht, Sebastian JiroMon, 12 Feb 2018 12:13:42 +0200http://theses.eurasip.org/theses/766/feedback-delay-networks-in-artificial/Informed spatial filters for speech enhancementhttp://theses.eurasip.org/theses/765/informed-spatial-filters-for-speech-enhancement/In modern devices which provide hands-free speech capturing functionality, such as hands-free communication kits and voice-controlled devices, the received speech signal at the microphones is corrupted by background noise, interfering speech signals, and room reverberation. In many practical situations, the microphones are not necessarily located near the desired source, and hence, the ratio of the desired speech power to the power of the background noise, the interfering speech, and the reverberation at the microphones can be very low, often around or even below 0 dB. In such situations, the comfort of human-to-human communication, as well as the accuracy of automatic speech recognisers for voice-controlled applications can be signi cantly degraded. Therefore, e ffective speech enhancement algorithms are required to process the microphone signals before transmitting them to the far-end side for communication, or before feeding them into a speech recognition ...Taseska, MajaWed, 07 Feb 2018 23:57:49 +0200http://theses.eurasip.org/theses/765/informed-spatial-filters-for-speech-enhancement/High-End Performance with Low-End Hardware: Analysis of Massive MIMO Base Station Transceivershttp://theses.eurasip.org/theses/764/high-end-performance-with-low-end-hardware/Massive MIMO (multiple-input–multiple-output) is a multi-antenna technology for cellular wireless communication, where the base station uses a large number of individually controllable antennas to multiplex users spatially. This technology can provide a high spectral efficiency. One of its main challenges is the immense hardware complexity and cost of all the radio chains in the base station. To make massive MIMO commercially viable, inexpensive, low-complexity hardware with low linearity has to be used, which inherently leads to more signal distortion. This thesis investigates how the degenerated linearity of some of the main components—power amplifiers, analog-to-digital converters (ADCs) and low-noise amplifiers—affects the performance of the system, with respect to data rate, power consumption and out-of-band radiation. The main results are: Spatial processing can reduce PAR (peak-to-average ratio) of the transmit signals in the downlink to as low as 0B; this, however, does ...Mollén, ChristopherTue, 06 Feb 2018 14:56:58 +0200http://theses.eurasip.org/theses/764/high-end-performance-with-low-end-hardware/Measurement Methods for Estimating the Error Vector Magnitude in OFDM Transceivershttp://theses.eurasip.org/theses/763/measurement-methods-for-estimating-the-error/The error vector magnitude (EVM) is a standard metric to quantify the performance of digital communication systems and related building blocks. Regular EVM measurements require expensive equipment featuring inphase and quadrature (IQ) demodulation, wideband analog-to-digital converters (ADCs), and dedicated receiver algorithms to demodulate the data symbols. With modern high data rate communication standards that require high bandwidths and low amounts of error, it is difficult to avoid bias due to errors in the measurement chain. This thesis develops and discusses measurement methods that address the above-described issues with EVM measurements. The first method is an extension of the regular EVM, yielding two results from a single measurement. One result equals the regular EVM result, whereas the other excludes potential errors due to mismatches of the I- and Q- paths of direct conversion transmitters and receivers (IQ imbalance). This can be ...Freiberger, KarlTue, 06 Feb 2018 11:26:40 +0200http://theses.eurasip.org/theses/763/measurement-methods-for-estimating-the-error/Filter Bank Multicarrier Modulation for Future Wireless Systemshttp://theses.eurasip.org/theses/762/filter-bank-multicarrier-modulation-for-future/Future wireless systems will be characterized by a large range of possible use cases. This requires a flexible allocation of the available time-frequency resources, which is difficult in conventional Orthogonal Frequency Division Multiplexing (OFDM). Thus, modifications of OFDM, such as windowing or filtering, become necessary. Alternatively, one can employ a different modulation scheme, such as Filter Bank Multicarrier Modulation (FBMC). In this thesis, I provide a unifying framework, discussion and performance evaluation of FBMC and compare it to OFDM based schemes. My investigations are not only based on simulations, but are substantiated by real-world testbed measurements and trials, where I show that multiple antennas and channel estimation, two of the main challenges associated with FBMC, can be efficiently dealt with. Additionally, I derive closed-form solutions for the signal-to-interference ratio in doubly-selective channels and show that in many practical cases, one-tap ...Nissel, RonaldThu, 01 Feb 2018 16:34:49 +0200http://theses.eurasip.org/theses/762/filter-bank-multicarrier-modulation-for-future/A Contribution to Efficient Direction Finding using Antenna Arrayshttp://theses.eurasip.org/theses/761/a-contribution-to-efficient-direction-finding/It is save to say that there is no such thing as the direction finding (DF) algorithm. Rather, there are algorithms that are tuned to resolve hundreds of paths, algorithms that are designed for uniform linear arrays or uniform circular arrays, and algorithms that strive for efficiency. The doctoral thesis at hand deals with the latter type of algorithms. However, the approach taken does not only incorporate the actual DF algorithm but approaches the problem from different perspectives. The first perspective concerns the description of the array manifold. Current interpolation schemes have no notion of polarization. Hence, the array manifold interpolation is performed separately for each state of polarization. In this thesis, we adopted the idea of interpolation via a 2-D discrete Fourier transform. However, we transform the problem into the quaternionic domain. Here, a 2-D discrete quaternionic Fourier transform ...Neudert-Schulz, DominikWed, 31 Jan 2018 21:15:19 +0200http://theses.eurasip.org/theses/761/a-contribution-to-efficient-direction-finding/