Intercarrier Interference Reduction and Channel Estimation in OFDM Systems PDF Download

Author: Yihai Zhang
Publisher:
ISBN: 9780494824412
Category :
Languages : en
Pages :

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Author: Yihai Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
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 ...

Author: Sami Said Tarbosh Salam
Publisher:
ISBN:
Category : Orthogonal frequency division multiplexing
Languages : en
Pages : 162

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

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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.

Author: Adarsh B. Narasimhamurthy
Publisher: Morgan & Claypool Publishers
ISBN: 1598297015
Category : Computers
Languages : en
Pages : 79

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Book Description
Orthogonal Frequency Division Multiplexing (OFDM) systems are widely used in the standards for digital audio/video broadcasting, WiFi and WiMax. Being a frequency-domain approach to communications, OFDM has important advantages in dealing with the frequency-selective nature of high data rate wireless communication channels. As the needs for operating with higher data rates become more pressing, OFDM systems have emerged as an effective physical-layer solution. This short monograph is intended as a tutorial which highlights the deleterious aspects of the wireless channel and presents why OFDM is a good choice as a modulation that can transmit at high data rates. The system-level approach we shall pursue will also point out the disadvantages of OFDM systems especially in the context of peak to average ratio, and carrier frequency synchronization. Finally, simulation of OFDM systems will be given due prominence. Simple MATLAB programs are provided for bit error rate simulation using a discrete-time OFDM representation. Software is also provided to simulate the effects of inter-block-interference, inter-carrier-interference and signal clipping on the error rate performance. Different components of the OFDM system are described, and detailed implementation notes are provided for the programs. The program can be downloaded here. Table of Contents: Introduction / Modeling Wireless Channels / Baseband OFDM System / Carrier Frequency Offset / Peak to Average Power Ratio / Simulation of the Performance of OFDM Systems / Conclusions

Author: Adarsh Narasimhamurthy
Publisher: Springer Nature
ISBN: 3031015134
Category : Technology & Engineering
Languages : en
Pages : 68

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Book Description
Orthogonal Frequency Division Multiplexing (OFDM) systems are widely used in the standards for digital audio/video broadcasting, WiFi and WiMax. Being a frequency-domain approach to communications, OFDM has important advantages in dealing with the frequency-selective nature of high data rate wireless communication channels. As the needs for operating with higher data rates become more pressing, OFDM systems have emerged as an effective physical-layer solution. This short monograph is intended as a tutorial which highlights the deleterious aspects of the wireless channel and presents why OFDM is a good choice as a modulation that can transmit at high data rates. The system-level approach we shall pursue will also point out the disadvantages of OFDM systems especially in the context of peak to average ratio, and carrier frequency synchronization. Finally, simulation of OFDM systems will be given due prominence. Simple MATLAB programs are provided for bit error rate simulation using a discrete-time OFDM representation. Software is also provided to simulate the effects of inter-block-interference, inter-carrier-interference and signal clipping on the error rate performance. Different components of the OFDM system are described, and detailed implementation notes are provided for the programs. The program can be downloaded here. Table of Contents: Introduction / Modeling Wireless Channels / Baseband OFDM System / Carrier Frequency Offset / Peak to Average Power Ratio / Simulation of the Performance of OFDM Systems / Conclusions

Author: Jie Gao
Publisher:
ISBN:
Category : MIMO systems
Languages : en
Pages : 210

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Book Description
Designing spectral efficient, high-speed wireless links that offer high quality- of-service and range capability has been a critical research and engineering challenge. In this thesis, we mainly address the complexity and performance issues of channel estimation and data detection in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems over time-varying channels. We derive the probability density function (pdf) expressions of the condition number (i.e., the maximum-to-minimum-singular-value ratio, MMSVR) of the channel state information matrix of MIMO OFDM systems. It is shown that this ratio is directly related to the noise enhancement in open-loop systems and provides a significant insight on the system capacity. A decision-directed (DD) maximum a posteriori probability (MAP) channel estimation scheme of MIMO systems is derived. Error performance of a zero- forcing receiver with the DD MAP and perfect channel estimates is provided and compared. This scheme has a low complexity and can be applied to time-varying Rayleigh fading channels with an arbitrary spaced-time correlation function. We propose an iterative channel estimation and data detection scheme for MIMO OFDM systems in the presence of inter-carrier-interference (ICI) due to the nature of time-varying channels. An ICI-based minimum-mean-square error (MMSE) detection scheme is derived. An expectation-maximization (EM) based least square (LS) channel estimator is proposed to minimize the mean-square error (MSE) of the channel estimates and to reduce the complexity of the implementation. With the estimate of the channel and initially detected symbols, ICI is estimated and removed from the received signal. Thus more accurate estimation of the channel and data detection can be obtained in the next iteration. An EM-based MAP channel estimator is derived by exploiting the frequency/time correlation of the pilot and data sub-carriers. Performance comparison is made between the proposed schemes and the ideal case - time-invariant channels and perfect channel estimation. We optimize the data transmission by exploiting the long term correlation characteristics. The transmitted data is successively detected without an error floor in spatially correlated channels. The algorithms proposed in this thesis allow low-complexity implementation of channel estimation and data detection for MIMO OFDM systems over time-varying fading channels, while providing good error performance.

Author: Yufei Jiang
Publisher: Springer
ISBN: 3319249843
Category : Computers
Languages : en
Pages : 96

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Book Description
This SpringerBrief investigates the performance of semi-blind independent component analysis (ICA) based equalization and carrier frequency offset estimation approaches (CFO) for a number of orthogonal frequency division multiplexing (OFDM) based wireless communication systems. It provides a comprehensive overview of the challenges of channel equalization and frequency synchronization for different wireless systems. The authors present the wireless communication channel and system models. Key existing CFO estimation methods are reviewed, along with a number of the training based and non-training based (blind) channel estimation methods. This is followed by a study of ICA and its applications to OFDM-based wireless communication systems. Later chapters provide a detailed description of recent research on semi-blind CFO estimation and ICA based equalization approaches for various wireless communication systems including multiple-input multiple-output (MIMO) OFDM and coordinated multipoint (CoMP) systems. Semi-blind CFO estimation and equalization structures provide a spectrum-efficient and high-performance solution for high speed wireless communications. This book is suitable for postgraduate students, researchers or professionals in the area of wireless communications.

Author: Yi Wang
Publisher:
ISBN:
Category :
Languages : en
Pages :

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"Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for high data rate transmission, that is widely used in modern wireless communication systems because of its good performance over frequency selective channels. However OFDM systems are sensitive to channel time variation resulting in Inter-Carrier Interference (ICI), that without suitable detection methods can degrade performance. Channel State Information (CSI) is essential to various OFDM data detection schemes and its acquisition is a critical factor, in particular over time-varying channels. This work considers a technique for integrating the Kalman filter channel estimation with a version of Sphere Decoding (SD) adapted to OFDM detection. By modelling the OFDM system in frequency domain as a Multiple Input Multiple Output (MIMO) system, we derive a powerful SD technique for data detection. By approximating the channel matrix as banded, we are able to maintain a feasible complexity for SD and deliver competitive performance when compared to other existing scheme. For acquisition of CSI, the Basis Expansion (BE) method is used to model the time-varying channels and a Kalman filter is constructed for tracking. The Kalman filter employs decision-feedback from the SD, requiring only a low pilot symbol density, and hence improves bandwidth efficiency. The performance of this scheme is evaluated by Monte-Carlo computer simulations. Results show that compared with competing algorithm, this scheme provides performance gains. When it is used over moderate time-varying LTE channels, this scheme shows good performance even in the presence of carrier phase noise. " --

Author: Ahmad R.S. Bahai
Publisher: Springer Science & Business Media
ISBN: 030646974X
Category : Technology & Engineering
Languages : en
Pages : 224

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Book Description
Multi-carrier modulation, in particular orthogonal frequency division multiplexing (OFDM), has been successfully applied to a wide variety of digital communications applications for several years. Although OFDM has been chosen as the physical layer standard for a diversity of important systems, the theory, algorithms, and implementation techniques remain subjects of current interest. This book is intended to be a concise summary of the present state of the art of the theory and practice of OFDM technology. This book offers a unified presentation of OFDM theory and high speed and wireless applications. In particular, ADSL, wireless LAN, and digital broadcasting technologies are explained. It is hoped that this book will prove valuable both to developers of such systems, and to researchers and graduate students involved in analysis of digital communications, and will remain a valuable summary of the technology, providing an understanding of new advances as well as the present core technology.