Feature-based spectrum sensing techniques have emerged as good balance between energy-based techniques and coherent-based techniques, where the former require minimal prior information of the observed signal, and the latter have robust detection performance when the observed signal is very weak. In this thesis, we focus on pilot tone-aided detection as a feature-based detection class. We propose an improved pilot tone-aided spectrum sensor that utilizes the presence of the pilot tone and the overall energy of the received signal. We show that the optimal Neyman-Pearson detector is a weighted summation of a feature-based component and an energy-based component. The former provides coherent gains at the low signal-to-noise ratio (SNR) regime, whereas the latter provides non-coherent gains at moderate SNR levels. The proposed detector intelligently adapts its weights based on the SNR of the observed signal and the power allocation factor of the pilot tone. This helps it attain significant performance gains compared with the conventional pilot tone-aided detectors. In addition, we present suboptimal detectors that reduce the computational complexity. For instance, we demonstrate that moment estimators are effective techniques for spectrum sensing. Motivated by insights gained from the derivations of these moment estimators, we present a selective mean-variance estimator that performs well in the absence of the prior knowledge about the pilot tone. Moreover, we analyze the impact of two model uncertainties on the detection performance of the proposed detector: Noise uncertainty and imperfect pilot-matching. We show that unlike the energy detector, the proposed detector does not suffer from the SNR wall under the noise uncertainty model due to the coherent gains embedded in the feature-based component. Also, unlike existing pilot tone-aided detectors, the proposed detector is resilient against imperfect synchronization due to the non-coherent gains embedded in computing the overall energy of the signal. Also, we show that the proposed detector achieves the lowest sample complexity, leading to tangible improvements to the aggregate throughput of the secondary user. Extensive simulation and analytical results are provided to verify these conclusions. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2014-04-15 15:31:27.253

Due to the scarcity of frequency spectrum in view of the evolution of wireless communication technologies, the cognitive radio (CR) concept has been introduced to efficiently exploit the available spectrum. This concept consists in introducing unlicensed/secondary users (SU’s) in existing networks to share the spectrum of licensed/primary users (PU’s) without harming primary communications hence the name of “spectrum sharing” technique. We study in this dissertation, the capacity and the achievable rate of the secondary user within various communication settings. We, firstly, investigate the capacity of the (SU’s) at low power regime for Nakagami fading channels and present closed form of the capacity under various types of interference and/or power constraints. We explicitly characterize two regimes where either the interference constraint or the power constraint dictates the optimal power profile. Our framework also highlights the effects of different fading parameters on the secondary link ergodic capacity. Interestingly, we show that the low power regime analysis provides a specific insight on the capacity behavior of CR that has not been reported by previous studies. Next, we determine the spectral efficiency gain of an uplink CR Multi-Input Multi- Output (MIMO) system in which the SU is allowed to share the spectrum with the PU using a specific precoding scheme to communicate with a common receiver. Applied to Rayleigh fading channels, we show, through numerical results, that our proposed scheme enhances considerably the cognitive achievable rate. For instance, in case of a perfect detection of the PU signal, after applying Successive Interference Cancellation (SIC), the CR rate remains non-zero for high Signal to Noise Ratio (SNR) which is usually impossible when we only use space alignment technique. In addition, we show that the rate gain is proportional to the allowed interference threshold by providing a fixed rate even in the high SNR range. Finally, we study the impact of the broadcast approach and multi-layer coding on the throughput of CR systems for general fading channels. And we found that at the absence of the channel state information(CSI), we show that this improvement could be almost reached by 2-Layers coding. Then, we introduce a quantized CSI policy and highlight its improvement in terms of throughput before we study the rate when BA with quantized CSI is adopted. Numerical results show that the improvement of the additional layers is decreasing as the number of quantized regions increases.

This dissertation examines data transfers along the existing lines of cable TV. PLC equipment has been selected as the focus of this examination. The essay examines the question of Multicarrier modulation and focuses more specifically onto the problem of OFDM modulation, which is being used by the selected equipment. It further describes the process of integration of PLC equipment into the cable TV network, modifications of the CATV and the basic topology of the created data networks. The essay also offers a closer look onto a PLC modem and Head End from Corinex that have been used in the implementation of a data network in a selected rural settlement. The author has also raised the issue of the problems connected with cable wires connected with this particular type of data transfers and the solutions of some of the encountered problems. The characteristics of this network have then been measured during normal operation of the created network. Measurements have been carried out in order to determine the transfer speed on a physical and transfer level, the SNR of specific connections and the signal attenuation. The measurements have confirmed the suitability of the used PLC equipment for the purposes of data transfer along the cable TV lines as far as data speed and signal strength was concerned. A map of the particular cable TV lines and the PLC equipment has been included in the attachment.

This diploma thesis deals with existing regional disparities in Germany with focus on differences between north and south regions at NUTS I level. The main goal is to divide analysed regions into clusters of similar regions using cluster analysis and prove the existence of regional disparities between north and south of Germany. Regional differences are determined using a group of selected regional disparity indicators that reflect different aspects of economy and life in German regions. The aim is also to analyse the development trend of regional disparities in years 2006-2016 using β and δ convergence models. Results are subsequently interpreted from an economic point of view.

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Tracking multiple targets with uncertain target dynamics is a difficult problem, especially with nonlinear state and/or measurement equations. Random finite set theory provides a rigorous foundation to multitarget tracking problems. It provides a framework to represent the full multitarget posterior in contrast to other conventional approaches. However, the computational complexity of performing multitarget recursion grows exponentially with the number of targets. The Probability Hypothesis Density (PHD) filter, which only propagates the first moment of the multitarget posterior, requires much less computational complexity. This thesis addresses some of the essential issues related to practical multitarget tracking problems such as tracking target maneuvers, stealthy targets, multitarget tracking in a distributed framework. With maneuvering targets, detecting and tracking the changes in the target motion model also becomes important and an effective solution for this problem using multiple-model based PHD filter is proposed. The proposed filter has the advantage over the other methods in that it can track a timevarying number of targets in nonlinear/ non-Gaussian systems. Recent developments in stealthy military aircraft and cruise missiles have emphasized the need to t rack low SNR targets. The conventional approach of thresholding the measurements throws away potential information and thus results in poor performance in tracking dim targets. The problem becomes even more complicated when multiple dim targets are present in the surveillance region. A PHD filter based recursive track-before-detect approach is proposed in this thesis to track multiple dim targets in a computationally efficient way. This thesis also investigates multiple target tracking using a network of sensors. Generally, sensor networks have limited energy, communication capability and computational power. The crucial consideration is what information needs to be transmitted over the network in order to perform online estimation of the current state of the monitored system, whilst attempting to minimize communication overhead. Finally, a novel continuous approximation approach for nonlinear/ non-Gaussian Bayesian tracking system based on spline interpolation is presented. The resulting filter has the advantages over the widely-known discrete particle based approximation approach in that it does not suffer from degeneracy problems and retains accurate density over the state space. The filter is general enough to be applicable to nonlinear/non-Gaussian system and the density could even be multi-modal. / Thesis / Candidate in Philosophy

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Darbo tikslas - atlikti gęstančių sinusinių signalų modelių klasės įvertinimo metodų lyginamąją analizę, palyginant Kumaresan – Tufts ir DMUSIC metodus. Darbe trumpai aprašyta šių metodų teorinė dalis. Pagrindinis dėmesys skiriamas šių metodų eksperimentiniam palyginimui. Eksperimentams atlikti buvo sukurta grafinė vartotojo sąsaja MATLAB aplinkoje. Aprašyti atlikti eksperimentai skirti, polių tikslumo įvertinimo tyrimui bei slenkstinės SNR nustatymui. Nagrinėjami tiek lėtai gęstantys, tiek greitai gęstantys signalai. Pateikiami skaitinių eksperimentų rezultatai bei programiniai MATLAB kodai. / The aim of this study is the comparative analysis of damped sinusoidal signal model class estimation methods. Two methods – Kumaresan – Tufts and DMUSIC – are compared. Theoretical preliminaries of these methods are described briefly in the work. The main attention is paid to experimental comparison of these methods. In order to conduct experiments, a MATLAB graphical user interface was created. The experiments devoted to investigation of poles estimation accuracy and to determining of the threshold and SNR. Both slowly damped and quickly damped signals are considered. The results of numerical experiments are presented and MATLAB programs are given.

Made available in DSpace on 2016-04-04T18:31:21Z (GMT). No. of bitstreams: 1 Marcelo Aparecido Morales.pdf: 2213720 bytes, checksum: 6858d1301ee70451e07970bdb465607e (MD5) Previous issue date: 2008-02-15 / The IEEE 802.11 wireless local area network presents a MAC anomaly when stations with different bit rates are connected in the same Access Point. Stations with high SNR have worst performance than stations with low SNR. This condition is worse in PWLANs (Public Wireless Local Area Network) with users connecting with different bit rates. This paper proposes a policy that uses the SNR and the condition of propagation to control users Contention Window. With this policy it is possible to control the Bit Rate, which is not possible in the 802.11 networks. / Redes 802.11 apresentam uma anomalia quando existem esta??es com diferentes taxas conectadas a um mesmo ponto de acesso. Esta??es com boa SNR (Signal-to-Noise Rate) obt?m um desempenho pior que esta??es com pior SNR. Esta condi??o ? esperada de forma agravada em redes p?blicas com v?rios usu?rios se conectando a diferentes taxas. Neste trabalho ? proposta uma pol?tica atrav?s da varia??o da janela de conten??o, levando em considera??o a SNR e a condi??o de propaga??o do local. Com a pol?tica a ser apresentada ? poss?vel controlar a taxa de transmiss?o em fun??o da SNR, criando uma possibilidade n?o oferecida pela rede 802.11.