221,780 research outputs found
Advanced Algorithms for Satellite Communication Signal Processing
DizertaÄŤnĂ práce je zaměřena na softwarovÄ› definovanĂ© pĹ™ijĂmaÄŤe urÄŤenĂ© k ĂşzkopásmovĂ© druĹľicovĂ© komunikaci. KomunikaÄŤnĂ kanály druĹľicovĂ˝ch spojĹŻ zahrnujĂcĂch komunikaci s hlubokĂ˝m vesmĂrem jsou zatĂĹľeny vysokĂ˝mi ĂşrovnÄ›mi šumu, typicky modelovanĂ©ho AWGN, a silnĂ˝m DopplerovĂ˝m posuvem signálu zpĹŻsobenĂ˝m mimořádnou rychlostĂ pohybu objektu. DizertaÄŤnĂ práce pĹ™edstavuje moĹľnĂ© postupy Ĺ™ešenĂ vĂ˝poÄŤetnÄ› efektivnĂ digitálnĂ downkonverze ĂşzkopásmovĂ˝ch signálĹŻ a systĂ©mu odhadu kmitoÄŤtu nosnĂ© ĂşzkopásmovĂ˝ch signálĹŻ zatĂĹľenĂ˝ch DopplerovĂ˝m posuvem v řádu násobkĹŻ šĂĹ™ky pásma signálu. Popis navrhovanĂ˝ch algoritmĹŻ zahrnuje analytickĂ˝ postup jejich vĂ˝voje a tam, kde je to moĹľnĂ©, i analytickĂ© hodnocenĂ jejich chovánĂ. Algoritmy jsou modelovány v prostĹ™edĂ MATLAB Simulink a tyto modely jsou vyuĹľity pro ověřenĂ vlastnostĂ simulacemi. Modely byly takĂ© vyuĹľity k experimentálnĂm testĹŻm na reálnĂ©m signálu pĹ™ijatĂ©m z druĹľice PSAT v laboratoĹ™i experimentálnĂch druĹľic na Ăşstavu radioelektroniky.The dissertation is focused on software defined receivers intended for narrowband satellite communication. The satellite communication channel including deep space communication suffers from a high level of noise, typically modeled by AWGN, and from a strong Doppler shift of a signal caused by the unprecedented speed of an object in motion. The dissertation shows possible approaches to the issues of computationally efficient digital downconversion of narrowband signals and the carrier frequency estimation of narrowband signals distorted by the Doppler shift in the order of multiples of the signal bandwidth. The description of the proposed algorithms includes an analytical approach of its development and, if possible, the analytical performance assessment. The algorithms are modeled in MATLAB Simulink and the models are used for validating the performance by the simulation. The models were also used for experimental tests on the real signal received from the PSAT satellite at the laboratory of experimental satellites at the department of radio electronics.
Multiuser MIMO-OFDM for Next-Generation Wireless Systems
This overview portrays the 40-year evolution of orthogonal frequency division multiplexing (OFDM) research. The amelioration of powerful multicarrier OFDM arrangements with multiple-input multiple-output (MIMO) systems has numerous benefits, which are detailed in this treatise. We continue by highlighting the limitations of conventional detection and channel estimation techniques designed for multiuser MIMO OFDM systems in the so-called rank-deficient scenarios, where the number of users supported or the number of transmit antennas employed exceeds the number of receiver antennas. This is often encountered in practice, unless we limit the number of users granted access in the base station’s or radio port’s coverage area. Following a historical perspective on the associated design problems and their state-of-the-art solutions, the second half of this treatise details a range of classic multiuser detectors (MUDs) designed for MIMO-OFDM systems and characterizes their achievable performance. A further section aims for identifying novel cutting-edge genetic algorithm (GA)-aided detector solutions, which have found numerous applications in wireless communications in recent years. In an effort to stimulate the cross pollination of ideas across the machine learning, optimization, signal processing, and wireless communications research communities, we will review the broadly applicable principles of various GA-assisted optimization techniques, which were recently proposed also for employment inmultiuser MIMO OFDM. In order to stimulate new research, we demonstrate that the family of GA-aided MUDs is capable of achieving a near-optimum performance at the cost of a significantly lower computational complexity than that imposed by their optimum maximum-likelihood (ML) MUD aided counterparts. The paper is concluded by outlining a range of future research options that may find their way into next-generation wireless systems
Review of the mathematical foundations of data fusion techniques in surface metrology
The recent proliferation of engineered surfaces, including freeform and structured surfaces, is challenging current metrology techniques. Measurement using multiple sensors has been proposed to achieve enhanced benefits, mainly in terms of spatial frequency bandwidth, which a single sensor cannot provide. When using data from different sensors, a process of data fusion is required and there is much active research in this area. In this paper, current data fusion methods and applications are reviewed, with a focus on the mathematical foundations of the subject. Common research questions in the fusion of surface metrology data are raised and potential fusion algorithms are discussed
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