Author: Tianqi Wang
Publisher:
ISBN:
Category : Radio frequency modulation
Languages : en
Pages : 0

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Author: Paulo Montezuma
Publisher: CRC Press
ISBN: 1351689363
Category : Technology & Engineering
Languages : en
Pages : 153

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Frequency-Domain Receiver Design for Doubly-Selective Channels discusses broadband wireless transmission techniques, which are serious candidates to be implemented in future broadband wireless and cellular systems, aiming at providing high and reliable data transmission and concomitantly high mobility. This book provides an overview of the channel impairments that may affect performance of single carrier and multi-carrier block transmission techniques in mobile environments. Moreover, it also provides a new insight into the new receiver designs able to cope with double selectivity that affects present and future broadband high speed mobile communication systems.

Author: Mansour Tahernezhadi
Publisher:
ISBN: 9783838320717
Category :
Languages : en
Pages : 92

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Author: Bernardo Martínez Blas
Publisher:
ISBN:
Category :
Languages : en
Pages :

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In actual mobile radio systems, multipath conditions pose a problem, as the channel becomes frequency dependent. This point is especially critical in case of high frequency transmissions with very high data rate and high error performance, such as defined in the IEEE 802.15.3c which is an emerging 60-GHz standard supporting data rates of multi-giga bits per second (multi-Gbps) for short-range indoor applications. The deployment of such high speed wireless transmission has been very difficult throughout history mainly by two critical factors: the first one was the lack of wide enough spectrum and the second one is the high cost of high frequency circuits and devices. However, this trend is changing to the point that not too long ago, the substantial unlicensed spectrum became available at the millimeter-wave band of 60-GHz. Also, the advancement in technology drives the cost of 60-GHz circuits and devices much lower than in the past making possible its use for high definition audio and video wireless transmissions. In order to overcome the transmission channel issues, it is necessary to include a channel equalizer in the receiver, which must estimate the channel impulse response and make some operations to transform the frequency dependent channel to a flat channel. Nevertheless, the equalizer technology will depend on three different factors: first one the physical layer (PHY) technique under consideration for multi-Gbps Wireless Personal Area Network (WPAN) which basically could be orthogonal frequency division multiplexing (OFDM) or single-carrier frequency domain equalization (SC-FDE); second, the channel impulse response estimation carried out in order to determine the channel transfer function H(f), existing several methods to obtain an estimation; and third, the used equalization method and structure in order to reverse all distortions produced by the channel. This Master thesis has been carry out during an Erasmus program in the Technische Universitat of Braunchweig, Germany, and it is the first part of a whole European project for the study, analysis and deployment of the IEEE 802.15.3c standard for wireless communications with very high data rate and high error performance in the 60-GHz band. According to the instructions and requirements defined by professor Thomas Kürner which was in charge of this project, this thesis include: first, a theoretical study of all the different propagation effects which could affect a wireless communication channel in order to run not only the simulations presented in this thesis but also the future simulations; second, the development of a model in Matlab/Simulink that will be useful to carry out all the project simulations (taken into account the specifications collected in IEEE 802.15.3c standard); third, the results of the carried simulations for Single Carrier Channel estimation and equalization by using two different equalization methods in the frequency domain: Zero Forcing and Minimum Mean Square Error equalization. Taking this into account, the thesis is organized as follows. Section I is dedicated to the study of all the different propagation effects and problems which affects a wireless communication transmissions; In Section II, technologies and Physical Layer Modes are described attending the IEEE 802.15.3c in order to learn its different characteristics for the subsequent channel estimation; Section III is devoted to channel estimation and equalization methods description; estimation and equalization methods are selected in order to carry out the simulations in Section IV; finally, in Section V the developed system simulator as well as the obtained simulation results are presented after implementation of Zero Forcing and Minimum Mean Square Error equalization methods in Matlab/Simulink.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 6

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In this paper we investigate adaptive channel estimation for frequency domain equalization (FDE) in a single carrier (SC) multiple-input multiple-output (MIMO) system. Two types of channel estimation methods are proposed, assuming uncorrelated and correlated frequency bins. The FDE coefficients are computed using the channel estimates. It is shown that our proposed structures significantly outperform the adaptive FDE without channel estimation at high SNR. In particular, the proposed LMS-SCE FDE approaches the performance of FDE with perfect channel state information (CSI), and has a fast convergence speed and reasonably low complexity.

Author: Lajos Hanzo
Publisher: Wiley-IEEE Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 760

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Adaptive Wireless Transceivers provides the reader with a broad overview of near-instantaneously adaptive transceivers in the context of TDMA, CDMA and OFDM systems. The adaptive transceivers examined employ powerful turbo codecs, turbo equalisers and space-time codecs, equipping the reader with a future-proof technological road map. It demonstrates that adaptive transceivers are capable of mitigating the channel quality fluctuations of the wireless channel as a lower-complexity alternative to space-time coding. By contrast, if the higher complexity of multiple transmitters and multiple receiver-assisted systems is deemed acceptable, the advantages of adaptability erode. Provides an in-depth introduction to channel equalisers and Kalman filtering and discusses the associated complexity versus performance trade-offs Introduces wideband near-instantaneously adaptive transceivers and studies their performance both with and without turbo channel coding Describes how to optimise adaptive modulation mode switching and highlights a range of practical considerations Introduces neural network based channel equalisers and discusses Radial Basis Function (RBF) assisted equalisers embedded into adaptive modems supported by turbo channel coding and turbo channel equalisation Employs the above adaptive principles also in the context of CDMA and OFDM transceivers and discusses the pros and cons of space-time coding versus adaptive modulation Researchers, advanced students and practising development engineers working in wireless communications will all find this valuable text an informative read.

Author: Hong Liu
Publisher:
ISBN:
Category : Equalizers (Electronics)
Languages : en
Pages : 136

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Abstract: Wireless communication systems targeting at broadband and mobile transmissions commonly face the challenge of fading channels that are both time and frequency selective. Therefore, design of effective equalization and estimation algorithms for such channels becomes a fundamental problem. Although multi-carrier transmissions demonstrate prominent potential to combat doubly selective fading, several factors may retard their applications, such as: high peak-to-average power ratio, sensitivity to phase noise, etc. Meanwhile, single-carrier transmission is a conventional approach and has important applications, such as HDTV broadcasting, underwater acoustic communication. In this dissertation, we focus on receiver design for single-carrier transmissions. Our goal is to design and develop a group of channel estimation and equalization algorithms in the frequency-domain, which enable high performance and low complexity reception of single-carrier transmissions through doubly selective channels. For single-carrier transmissions over moderately fast fading channels with long-delay spread, we present an improved iterative frequency-domain equalization (IFDE) algorithm based on soft-interference-cancellation (SIC) and propose a novel adaptive frequency-domain channel estimation (AFDCE) based on soft-input Kalman filter, where soft information feedback from the IFDE can be exploited in the channel estimator. Simulation results show that, compared to other existing schemes, the proposed scheme offers lower MSE in channel prediction, lower BER after decoding, and robustness to non-stationary channels. We extend the IFDE/AFDCE scheme to accommodate the application of digital television (DTV) signal reception. Compared with the traditional joint decision feedback equalization (DFE) /decoding plus frequency-domain least-mean-square (FDLMS) channel estimation approach, the proposed scheme achieves better performance at a fraction of the implementation cost. For very fast fading large-delay-spread channels, traditional FDE methods fail, because channel variation within a FFT block induces significant off-main-diagonal coefficients in the frequency domain. To conquer the problem, we apply Doppler channel shortening to shape the energy distribution of those coefficients and derive a pilot-aided MMSE estimator to estimate them for SIC. We also propose a novel IFDE by leveraging both the sparse structure of shortened channel and finite-alphabet property of transmitted symbols. Numerical results show that the proposed scheme has advantages over the well-known FIR-MMSE-DFE/RLS-CE scheme in both performance and complexity.

Author:
Publisher:
ISBN:
Category :
Languages : pt-BR
Pages :

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Crescimento dos sistemas de comunicações móveis celulares e dos sistemas de rádio difusão de sinais de áudio e vídeo tem despertado grande interesse na pesquisa de novos métodos para a transmissão de sinais nestas redes. A necessidade de se transmitir dados em altas taxas, com significante eficiência no uso da largura de faixa de freqüências disponível, e por meio de um canal de propagação ruidoso e variante no tempo, constitui o principal problema para o desenvolvimento de novas técnicas de trasmissão de sinais. Dentro deste contexto, esta dissertação trata do uso dos conceitos de transmissão digital e filtragem adaptativa para a demodulação de sinais OFDM (Orthogonal Frequency Division Multiplexing). A equalização de sinais antes e após o estágio de DFT (Discrete Fourier Transform) no receptor e as técnicas de estimação de canal são o objeto principal de estudo deste trabalho. Os resultados dos experimentos são analisados em termos da taxa de erro de bit média obtida e da convergência dos algoritmos empregados nas etapas de equalização e estimação de canal no receptor.

Author: Lajos Hanzo
Publisher: John Wiley & Sons
ISBN: 0470031379
Category : Technology & Engineering
Languages : en
Pages : 430

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Book Description
Wireless communications has witnessed a tremendous growth during the past decade and further spectacular enabling technology advances are expected in an effort to render ubiquitous wireless connectivity a reality. Currently, a technical in-depth book on this subject is unavailable, which has a similar detailed exposure of OFDM, MIMO-OFDM and MC-CDMA. A further attraction of the joint treatment of these topics is that it allows the reader to view their design trade-offs in a comparative context. Divided into three main parts: Part I provides a detailed exposure of OFDM designed for employment in various applications Part II is another design alternative applicable in the context of OFDM systems where the channel quality fluctuations observed are averaged out with the aid of frequency-domain spreading codes, which leads to the concept of MC-CDMA Part III discusses how to employ multiple antennas at the base station for the sake of supporting multiple users in the uplink By providing an all-encompassing self-contained treatment this volume will appeal to a wide readership, as it is both an easy-reading textbook and a high-level research monograph.

Author: Ali Salah Mahdi
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659671616
Category :
Languages : en
Pages : 84

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Book Description
Orthogonal Frequency Division Multiplexing (OFDM) system is one of the multicarrier techniques which is robust against Inter-symbol-Interference, multipath fading and very easy to apply in transmitters by using inverse fast Fourier transform IFFT and at the receivers by using fast Fourier transform FFT. In a communication system, channel estimation is very important issue for the data detection. In coherent detection, one of the popular techniques is to use pilot tones as a reference signal in OFDM symbols. In the comb-type pilot tones insertion, pilot tones are inserted into each OFDM symbols, but inserting a large number of pilot tones will lead to channel capacity reduction or bandwidth expansion [1-2]. In this work, to overcome this transmission loss, a modified least square (ModLS) algorithm for fast time varying wireless channel at comb-type pilot arrangement in QAM signals for OFDM system is proposed. The simulation results obtained from the proposed algorithm showed a good performance in noisy wireless channels. In addition, it has been compared with least square (LS) algorithm in different signal to noise ratios and different channel tabs.