Orientador: Celso de Almeida, Rodrigo Pereira Ramos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-08T10:36:25Z (GMT). No. of bitstreams: 1 Britto_PauloMarceloPerezRodriguesde_M.pdf: 4780408 bytes, checksum: c3b152e041128b5d94429d8b87c0068c (MD5) Previous issue date: 2006 / Resumo: O desempenho de sistemas de comunicações sem fio que utilizam técnicas de espalhamento espectral e múltiplo acesso por divisão de código (CDMA) é limitado pela interferência. Nesta dissertação, analisamos o desempenho de um algoritmo de seleção de seqüências de espalhamento de comprimento fixo, que busca a minimização dos efeitos de interferência em sistemas CDMA operando em canais com desvanecimento seletivo em freqüência e possuindo células adjacentes interferentes. Analisamos o desempenho deste sistema no qual o espalhamento espectral é feito usando duas seqüências: seqüências do usuário e seqüências identificadoras de células. Dentre as seqüências analisadas, podemos citar as Walsh, a Gold, as de comprimento máximo e também um tipo de seqüência de espalhamento baseado nas seqüências de comprimento máximo / Abstract: The performance of wireless communication systems using spread spectrum techniques and code division multiple access (CDMA) is interference-limited. In this dissertation, we evaluate the performance of a selection algorithm for fixed-length spreading sequences, aimed on minimizing the interference effects in CDMA systems operating in frequency selective fading channels and having adjacent interfering cells. We check the performance of this system where the spread spectrum operation is performed using two sequences: user sequences and cell identification sequences. Among the sequences considered, we use Walsh, Gold, maximum length and a type of spreading sequence based on the maximum length class / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Spread Spectrum Communication techniques have been widely used in mobile and wireless communications. They have very beneficial features like antijam and security (noise-like character, pseudorandom codes usage). At first, the features of Spread Spectrum systems are described with emphasis on the Direct Sequence Spread Spectrum (DS-SS) scheme. Main specifications of UMTS system are also introduced. The goal of this thesis was to create the model of a physical layer UMTS suitable for investigation of disturbing signals influences in Matlab Simulink. This model was used to measure how the Bit error rate (BER) is affected by the Processing gain and the Signal-to-noise ratio. Finally, two important charts which describe the relation of Bit error rate versus the Processing gain and the Signal-to-noise ratio have been plotted.

This Thesis deals with a method to enforce the intellectual property rights and protect digital media from tampering – Digital Audio Watermarking. The main aim of this work is implement an audio watermarking algorithm. The theoretical part defined basic terms, methods and processes, which are used in this area. The practical part shows a process of embedding the digital signature into a host signal and her backward extraction. The embedding rule used spread spectrum technique and a psychoacoustic model. The implemented psychoacoustic model involves two properties of the human auditory system which are frequency masking and representation the frequency scale on limited bands called critical bands. The model is relatively new and based on the DWPT. In terms of above model is then the digital watermark embedded in the wavelet domain. This algorithm is implemented in technical software MATLAB. One part of this work focuses on robustness tests of the algorithm. Common signal processing modifications are applied to the watermarked audio as follows: Cutting of the audio, re-sampling, lossy compression, filtering, equalization, modulation effects, noise addition. The last part of the thesis presents subjective and objective methods usable in order to judge the influence of watermarking embedding on the quality of audio tracks called transparency.

Ultra-wideband (UWB) communication new technology with ability to share the FCC allocated frequency spectrum, large channel capacity and data rate, simple transceiver architecture and high performance in noisy environments. Such communication advantages have paved the way for emerging wireless technologies such as wireless high definition video streaming, wireless sensor networks and more. This thesis examines orthogonal frequency coded surface acoustic wave (SAW) correlators for use in advanced UWB communication systems. Orthogonal frequency coding (OFC) and pseudo-noise (PN) coding provides a means for UWB spreading of data. The use of OFC spectrally spreads a PN sequence beyond that of CDMA because of the increased bandwidth; allowing for improved correlation gain. The transceiver approach is still very similar to that of the CDMA approach but provides greater code diversity. Use of SAW correlators eliminates many of the costly components that are needed in the IF block in the transmitter and receiver, and reduces much of the signal processing requirements. The OFC SAW correlator device consists of a dispersive OFC transducer and a wideband output transducer. The dispersive filter was designed using seven contiguous chip frequencies within the transducer. Each chip is weighted in the transducer to account for the varying conductance of the chips and to compensate for the output transducer apodization. Experimental correlator results of an OFC SAW correlation filter are presented. The dispersive filter is designed using seven contiguous chip frequencies within the transducer. SAW correlators with fractional bandwidth of approximately 29% were fabricated on lithium niobate (LiNbO3) having a center frequency of 250 MHz and the filter has a processing gain of 49. A coupling of modes (COM) model is used to predict the experimental SAW filter response. Discussion of the filter design, analysis and measurements are presented. Results are shown for operation in a matched filter correlator for use in an UWB communication system and compared to predictions.

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Radio wave propagation measurements provide a way to accurately and reliably characterize environments to assist in the development and optimization of wireless communication systems. As digital radio systems occupy wider bandwidths and use multipath signal combining to enhance quality of service, knowledge of time dispersion and the multipath structure of radio channels become increasingly important. The wideband measurement system presented herein provides a practical means to precisely measure the delays and strengths of individual multipath components which arrive at a radio receiver. Presented in this Thesis are fundamental theory, practical implementation, and simulation models for a sliding correlator measurement system. The sliding correlator technique is explained in detail and large-scale measurement survey is presented. Techniques for statistically quantifying the characteristics of propagation using the sliding correlator measurements are presented and compared. The development of simulations of the sliding correlator system is described, and simulation results are used to test conventional and newly developed post-processing algorithms. This Thesis presents a practical view of the sliding correlator measurement system, but its foundations are rooted in the theoretical results which are explained and derived herein. Propagation researchers and students in the wireless communication field may find this work and the cited references useful for continued study of wideband propagation measurements or for application of the sliding correlator system as a wideband measurement solution. / Master of Science

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / Eglin Air Force Base (AFB) plans to demonstrate subminiature telemetry (SMT) spread spectrum technology, via an upgraded prototype SMT system, to validate its cost-effectiveness for both Department of Defense (DoD) and commercial use. The goal is to develop new and/or modify current SMT instrumentation using existing production methods to provide increased capabilities at lower costs and reduced size. The transmitter is to require less than 2 cubic inches of space and have a cost goal of $500/unit "in quantity." The cost goal of a ground-based, 24-channel capable ground receiver is $4000/unit "in quantity". The SMT project as well as its schedule, flight and ground demonstrations, validation criteria and goals, and various benefits are discussed.

Approved for public release, distribution is unlimited / Direct-Sequence Spread Spectrum (DSSS) modulation is being advanced as the physical-layer basis for Seaweb undersea acoustic networking. DSSS meets the need for channel tolerance, transmission security, and multi-user access. This thesis investigates the performance of subspace-decomposition blind-equalization algorithms as alternatives to RAKE processing of DSSS signals. This approach is tailored for superior performance in time-dispersive and frequency-dispersive channels characteristic of ocean acoustic propagation. Transmitter and receiver structures are implemented in Matlab and evaluated with a statistics-based model of a doubly spread channel with additive noise. Receiver performance is examined using Monte Carlo simulation. Biterror rates versus signal-to-noise ratio are presented for various multipath assumptions, noise assumptions, and receiver synchronization assumptions. / Lieutenant, Hellenic Navy

Time Average Fourier Telescopy (TAFT) has been proposed as a means for obtaining high-resolution, diffraction-limited images over large distances through ground-level horizontal-path atmospheric turbulence. Image data is collected in the spatial-frequency, or Fourier, domain by means of Fourier Telescopy; an inverse two dimensional Fourier transform yields the actual image. TAFT requires active illumination of the distant object by moving interference fringe patterns. Light reflected from the object is collected by a “light-bucket” detector, and the resulting electrical signal is digitized and subjected to a series of signal processing operations, including an all-critical averaging of the amplitude and phase of a number of narrow-band signals. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection