Download or read book Intercarrier Interference Suppression for the OFDM Systems in Time varying Multipath Fading Channels written by Xiaozhou Huang and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis and Cancellation of Inter carrier Interference for OFDM Systems Over Time variant Multipath Fading Channels written by Yunjun Zhang and published by . This book was released on 2002 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The orthogonality among the subcarriers of OFDM systems may be impaired by the time-selectivity of the fading channels. The loss of the orthogonality results in ICI, and if it is not treated appropriately, the system performance may not be improved only by increasing the signal-to-noise ratio. In other words, ICI results in error floors. This research work concentrates on the ICI analysis and cancellation, and also on the effects of channel time-selectivity on the OFDM systems over frequency-selective time-variant mobile fading channels. In the first part of this study, a general time-variant frequency-selective WSSUS fading channel model is further characterized to support the OFDM ICI analysis, thus the obtained results are applicable for many specific channels. We then identify the cause of the ICI, i.e. how the orthogonality among the subcarriers of OFDM systems is impaired. The average ICI power and its distribution are obtained based on the general time-variant frequency-selective WSSUS fading channel model. To mitigate the ICI caused by the channel time-selectivity for OFDM systems, in the second part of this study, an efficient ICI cancellation scheme is designed based on the obtained ICI power distribution. The simulation results indicate that a significant performance improvement can be achieved. For OFDM systems, differential encoding can be performed not only between the information bits of the same subcarrier of the consecutive OFDM symbols (inter-frame differential encoding), but also between the information bits of the adjacent subcarriers of the same OFDM symbol (inter-carrier differential encoding). In the third part of this study, we compare the performance of inter-frame and inter-carrier differential detection for OFDM systems over multipath time-variant mobile fading channels. The objective is to identify which differential encoding scheme (inter-frame or inter-carrier) is more robust to the channel time-selectivity, when OFDM systems are experiencing both frequency-selective and time-selective fading. The conditions under which the inter-carrier differential encoding outperforms the inter-frame differential encoding and vice-versa are provided.

Download or read book Performance improving Techniques for Wireless Systems written by Orhan Can Ozdural and published by . This book was released on 2007 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis also presents a maximum likelihood approach exploiting the OFDM pilot subcarriers to suppress phase noise due to imperfect local oscillators. This algorithm does not require perfect channel equalization and is applicable for the two common types of oscillators: phase-locked and free-running oscillators. Furthermore, doubly-selective fading is considered rather than assuming time-invariant and/or flat fading channels.

Download or read book Intercarrier Interference Reduction and Channel Estimation in OFDM Systems written by Yihai Zhang and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: With the increasing demand for more wireless multimedia applications, it is desired to design a wireless system with higher data rate. Furthermore, the frequency spectrum has becomea limited and valuable resource, making it necessary to utilize the available spectrum efficiently and coexist with other wireless systems. Orthogonal frequency division multiplexing (OFDM)modulation is widely used in communication systems to meet the demand for ever increasing data rates. The major advantage of OFDM over single-carrier transmission is its ability to deal with severe channel conditions without complex equalization. However, OFDM systems suffer from a high peak to average power ratio, and they are sensitive to carrier frequency offset and Doppler spread. This dissertation first focuses on the development of intercarrier interference (ICI) reduction and signal detection algorithms for OFDM systems over time-varying channels. Several ICI reduction algorithms are proposed for OFDM systems over doubly-selective channels. The OFDM ICI reduction problem over time-varying channels is formulated as a combinatorial optimization problem based on the maximum likelihood (ML)criterion. First, two relaxation methods are utilized to convert the ICI reduction problem into convex quadratic programming (QP) problems. Next, a low complexity ICI reduction algorithm applicable to $M$-QAM signal constellations for OFDM systems is proposed. This formulates the ICI reduction problem as a QP problem with non-convex constraints. A successive method is then utilized to deduce a sequence ofreduced-size QP problems. For the proposed algorithms, the QPproblems are solved by limiting the search in the 2-dimensional subspace spanned by its steepest-descent and Newton directions to reduce the computational complexity. Furthermore, a low-bit descent search (LBDS) is employed to improve the system performance. Performance results are given to demonstrate that the proposed ICI reduction algorithms provide excellent performance with reasonable computational complexity. A low complexity joint semiblind detection algorithm based on the channel correlation and noisevariance is proposed which does not require channel state information. The detection problem is relaxed to a continuous non-convex quadratic programming problem. Then an iterative method is utilized to deduce a sequence of reduced-size quadratic programming problems. A LBDS method is also employed to improve the solution of the derived QP problems. Results are given which demonstrate that the proposed algorithm provides similar performance with lower computational complexity compared to that of a sphere decoder. A major challenge to OFDM systems is how to obtain accurate channel state information for coherent detection of the transmitted signals. Thus several channel estimation algorithms are proposed for OFDM systems over time-invariant channels. A channel estimation method is developed to utilize the noncircularity of the input signals to obtain an estimate of the channel coefficients ...

Download or read book Iterative Channel Estimation for Wireless Communications written by JoonBeom Kim and published by . This book was released on 2006 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Finally, for vertical Bell Laboratories layered space-time OFDM systems, we propose an iterative channel estimator based on a PSAM structure for time-varying multipath fading channels. By exploiting the statistical properties of a wireless channel, we also develop a method to suppress intercarrier interference due to the channel time selectivity, and propose a low-complexity iterative channel estimator that exploits a priori information in an efficient manner.

Download or read book Design of Channel Estimation and Equalization for OFDM Systems written by Ali Salah Mahdi and published by LAP Lambert Academic Publishing. This book was released on 2015-01-20 with total page 84 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Channel Estimation Techniques for OFDM Systems in Dispersive Time varying Channels written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Coherent modulation is more effective than differential modulation for orthogonal frequency division multiplexing (OFDM) systems requiring high data rate and spectral efficiency. Channel estimation is therefore an integral part of the receiver design. In this thesis, two iterative maximum likelihood based channel estimation algorithms are proposed for an OFDM system in dispersive time-varying channels. A multipath channel model is proposed for OFDM uplink transmission in macrocellular systems. The multipath fading channel is modeled such that the channel state can be determined by estimating the unknown channel parameters. A second-order Taylor series expansion is adopted to simplify the channel estimation problem. Based on the system model, an iterative maximum likelihood based algorithm is first proposed to estimate the discrete-time channel parameters. The mean square error performance of the proposed algorithm is analyzed using a small perturbation technique. Based on a convergence rate analysis, an improved iterative maximum likelihood based channel estimation algorithm is presented using a successive overrelaxation method. Numerical experiments are performed to confirm the theoretical analyses and show the improvement in convergence rate of the improved algorithm.

Download or read book International Symposium on Fuzzy Systems Knowledge Discovery and Natural Computation FSKD 2014 written by Defu Zhang, Xiamen University, China and published by DEStech Publications, Inc. This book was released on 2014-09-02 with total page 657 pages. Available in PDF, EPUB and Kindle. Book excerpt: ICNC-FSKD is a premier international forum for scientists and researchers to present the state of the art of data mining and intelligent methods inspired from nature, particularly biological, linguistic, and physical systems, with applications to computers, circuits, systems, control, communications, and more. This is an exciting and emerging interdisciplinary area in which a wide range of theory and methodologies are being investigated and developed to tackle complex and challenging problems.

Download or read book Interference Suppression and Parameter Estimation in Wireless Communication Systems Over Time varing Multipath Fading Channels written by Jianqiang He and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rough Sets and Knowledge Technology written by Peng Wen and published by Springer Science & Business Media. This book was released on 2009-06-24 with total page 725 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book constitutes the refereed proceedings of the Fourth International Conference on Rough Sets and Knowledge Technology, RSKT 2009, held in Gold Coast, Australia, in July 2009. The 85 revised full papers papers presented together with 3 keynote papers and 2 special sessions were carefully reviewed and selected from 229 submissions. The papers are organized in topical sections on rough sets and computing, rough sets and data reduction, data mining and knowledge discovery, granular computing and cognitive computing, fuzzy sets and computing, knowledge technology and intelligent systems, computational intelligence and applications, image processing and understanding, and formal concept analysis.

Download or read book Machine Learning and Intelligent Communications written by Xuemai Gu and published by Springer. This book was released on 2018-01-20 with total page 699 pages. Available in PDF, EPUB and Kindle. Book excerpt: This two volume set constitutes the refereed post-conference proceedings of the Second International Conference on Machine Learning and Intelligent Communications, MLICOM 2017, held in Weihai, China, in August 2017. The 143 revised full papers were carefully selected from 225 submissions. The papers are organized thematically in machine learning, intelligent positioning and navigation, intelligent multimedia processing and security, intelligent wireless mobile network and security, cognitive radio and intelligent networking, intelligent internet of things, intelligent satellite communications and networking, intelligent remote sensing, visual computing and three-dimensional modeling, green communication and intelligent networking, intelligent ad-hoc and sensor networks, intelligent resource allocation in wireless and cloud networks, intelligent signal processing in wireless and optical communications, intelligent radar signal processing, intelligent cooperative communications and networking.

Download or read book Performance Analysis of Two branch Transmit Diversity Block Coded OFDM Systems in Time varying Multipath Rayleigh Fading Channels written by Ding-bing Lin and published by . This book was released on 2005 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mobile Fading Channels written by Matthias Pätzold and published by Wiley-Blackwell. This book was released on 2002-04 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mobile channel fading is a loss in transmission intensity caused by changes in the transmission medium. By dealing with the modelling, analysis and simulation of mobile fading channels this text provides a fundamental understanding of many issues in the area of mobile fading channel modelling.; The main topics addressed in the volume are: fundamentals of stochastic and deterministic channel models and modelling and simulation of frequency-nonselective and frequency-selective fading channels. The guide also features methods for the design and realization of efficient channel simulators and fast channel simulators and MATLAB-programs for the evaluation and simulation of mobile fading channels.

Download or read book Advances in Hybrid Information Technology written by Marcin S. Szczuka and published by Springer Science & Business Media. This book was released on 2007-12-12 with total page 682 pages. Available in PDF, EPUB and Kindle. Book excerpt: Complete with online files and updates, this important new volume covers many of the areas in which hybrid information technology is advancing. The book is the thoroughly refereed post-proceedings of the First International Conference on Hybrid Information Technology, held in Korea in 2006. More than 60 revised papers were carefully selected during a second round of reviewing from 235 reports given at the conference, and are presented in extended version in the book.

Download or read book Wireless Communications Over Rapidly Time Varying Channels written by Franz Hlawatsch and published by Academic Press. This book was released on 2011-05-04 with total page 457 pages. Available in PDF, EPUB and Kindle. Book excerpt: As a result of higher frequencies and increased user mobility, researchers and systems designers are shifting their focus from time-invariant models to channels that vary within a block. Wireless Communications Over Rapidly Time-Varying Channels explains the latest theoretical advances and practical methods to give an understanding of rapidly time varying channels, together with performance trade-offs and potential performance gains, providing the expertise to develop future wireless systems technology. As well as an overview of the issues of developing wireless systems using time-varying channels, the book gives extensive coverage to methods for estimating and equalizing rapidly time-varying channels, including a discussion of training data optimization, as well as providing models and transceiver methods for time-varying ultra-wideband channels. An introduction to time-varying channel models gives in a nutshell the important issues of developing wireless systems technology using time-varying channels Extensive coverage of methods for estimating and equalizing rapidly time-varying channels, including a discussion of training data optimization, enables development of high performance wireless systems Chapters on transceiver design for OFDM and receiver algorithms for MIMO communication channels over time-varying channels, with an emphasis on modern iterative turbo-style architectures, demonstrates how these important technologies can optimize future wireless systems

Download or read book Analysis of Inter channel Interference Due to Multipath Fading Effect for ASK OFDM Systems written by Vishu Suvarna and published by . This book was released on 2003 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Co channel Interference Suppression for Ofdm Systems written by Jonghyun Won and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT: We propose new methods for co-channel interference suppression in orthogonal frequency division multiplexing (OFDM) systems with multiple receive antennas. Our methods use a low-order time-domain model to parameterize the matrix-valued spectral density of the noise and interference. A penalized maximum likelihood-function approach is used to choose the proper model order automatically in each received data frame. We show that these methods significantly improve the symbol-error-rate when interference exists in the received data. Numerical examples are provided to illustrate the performance of our new methods and compare with conventional methods. We also discuss the diplus or minusculties associated with the application of our method to space-time OFDM (ST-OFDM).