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Author: Publisher: ISBN: Category : Orthogonal frequency division multiplexing Languages : en Pages : 212
Book Description
In a traditional orthogonal frequency division multiplexing (OFDM) wireless communication system, a guard interval using cyclic prefix is injected to avoid an inter-symbol interference (ISI) and an inter-carrier interference (ICI). This approach has been proven to work well, however, only with time-variant channels wherein a high speed mobility element is not considered. Furthermore, a transmission in the OFDM system is considered a low efficiency due to the use of a large percentage of pilot data for channel estimation. In this research, an enhanced channel equalization in a multi-path propagation environment at a high frequency mobile network technologies is proposed. The multi-path propagation resulting from the variety of signal paths that may exist between the transmitter and receiver can give a rise to an interference in a variety of ways including distortion of the signal, loss of data and fading. These paths are created as a result of reflections from buildings, mountains, or other reflective surfaces. Having a high speed mobility system with high frequency mobile network technologies such as but not limited to 4G network lead to a frequency selective channel in the frequency domain and Inter-symbol Interference in the time domain. Furthermore, this phenomenon, i.e. high speed mobility causes a Doppler shift in which results into a time variant and frequency selective channel. Thus, we present a wireless communication channel scenario that is characterized and modeled by a high relative velocity between transmitter and receiver, and fast changes of environment conditions for wave propagation. Furthermore, we present a method for enhancing the equalization of such dynamic channel. Thus a dynamic channel is developed utilizing Jakes and auto-regressive models (AR). More specifically, the enhanced equalization method we are proposing is a combination of a multi-stage time and frequency domain equalizer with a feed-forward loop. Inserting pilot data at the transmitter and using said pilot data to estimate the channel in time domain. The addition of the feed-forward is utilized to capture a part of the received signal, then extracting the channel information while the signal is being delayed until the information is obtained. The estimated channel is forwarded to the MMSE equalizer. The first stage of the multi-stage equalizer is using pilot data as measurement data in the frequency domain. The second stage is to convert the measurement data to the time domain. In the third stage, we estimate the channel using the pilot data and use it as measurement data in the time domain, i.e. input to a Kalman filter. In OFDM system, the consecutive blocks for the channel coefficients for each tap in time domain are not totally independent, but partially correlated. Such correlation can improve the channel estimation when taken into account. Using the Kalman filter, we can extract this information from previous blocks and use them for the newly arrived one, and perform a better channel estimation. In the fourth stage, we use the output of the Kalman filter as a feed-forward to the frequency equalizer for each subcarrier in which the data is converted from time domain to frequency domain. The underlying wok (sic) presents a unified approach to the equalization approach that employs both time and frequency domains data to enhance the equalization scheme. In order to reduce the complexity of the system model, we utilize the autocorrelation and Doppler frequency to dynamically select the previous OFDM symbols that will be stored in the memory. In addition to deriving earlier results in a unified manner, the approach presented also leads to an enhanced performance results without imposing any restrictions or limitations on the OFDM system such as increasing the number of pilots or cyclic prefix.
Author: Publisher: ISBN: Category : Orthogonal frequency division multiplexing Languages : en Pages : 212
Book Description
In a traditional orthogonal frequency division multiplexing (OFDM) wireless communication system, a guard interval using cyclic prefix is injected to avoid an inter-symbol interference (ISI) and an inter-carrier interference (ICI). This approach has been proven to work well, however, only with time-variant channels wherein a high speed mobility element is not considered. Furthermore, a transmission in the OFDM system is considered a low efficiency due to the use of a large percentage of pilot data for channel estimation. In this research, an enhanced channel equalization in a multi-path propagation environment at a high frequency mobile network technologies is proposed. The multi-path propagation resulting from the variety of signal paths that may exist between the transmitter and receiver can give a rise to an interference in a variety of ways including distortion of the signal, loss of data and fading. These paths are created as a result of reflections from buildings, mountains, or other reflective surfaces. Having a high speed mobility system with high frequency mobile network technologies such as but not limited to 4G network lead to a frequency selective channel in the frequency domain and Inter-symbol Interference in the time domain. Furthermore, this phenomenon, i.e. high speed mobility causes a Doppler shift in which results into a time variant and frequency selective channel. Thus, we present a wireless communication channel scenario that is characterized and modeled by a high relative velocity between transmitter and receiver, and fast changes of environment conditions for wave propagation. Furthermore, we present a method for enhancing the equalization of such dynamic channel. Thus a dynamic channel is developed utilizing Jakes and auto-regressive models (AR). More specifically, the enhanced equalization method we are proposing is a combination of a multi-stage time and frequency domain equalizer with a feed-forward loop. Inserting pilot data at the transmitter and using said pilot data to estimate the channel in time domain. The addition of the feed-forward is utilized to capture a part of the received signal, then extracting the channel information while the signal is being delayed until the information is obtained. The estimated channel is forwarded to the MMSE equalizer. The first stage of the multi-stage equalizer is using pilot data as measurement data in the frequency domain. The second stage is to convert the measurement data to the time domain. In the third stage, we estimate the channel using the pilot data and use it as measurement data in the time domain, i.e. input to a Kalman filter. In OFDM system, the consecutive blocks for the channel coefficients for each tap in time domain are not totally independent, but partially correlated. Such correlation can improve the channel estimation when taken into account. Using the Kalman filter, we can extract this information from previous blocks and use them for the newly arrived one, and perform a better channel estimation. In the fourth stage, we use the output of the Kalman filter as a feed-forward to the frequency equalizer for each subcarrier in which the data is converted from time domain to frequency domain. The underlying wok (sic) presents a unified approach to the equalization approach that employs both time and frequency domains data to enhance the equalization scheme. In order to reduce the complexity of the system model, we utilize the autocorrelation and Doppler frequency to dynamically select the previous OFDM symbols that will be stored in the memory. In addition to deriving earlier results in a unified manner, the approach presented also leads to an enhanced performance results without imposing any restrictions or limitations on the OFDM system such as increasing the number of pilots or cyclic prefix.
Author: Chen Chen Publisher: Springer ISBN: 3030193926 Category : Technology & Engineering Languages : en Pages : 132
Book Description
This book introduces the sources and historic collection campaigns of resource allocation in wireless communication systems. The unique characteristics of MIMO-OFDMA systems are thoroughly studied and summarized. Remarks on resource allocation and spectrum sharing are also presented, which demonstrate the great value of resource allocation techniques, but also introduce distinct challenges of resource allocation in MIMO-OFDMA systems. Novel resource allocation techniques for OFDMA Systems are surveyed from various applications (e.g., for unicast, or multicast with Guaranteed BER and Rate, subcarrier and power allocation with various detectors, low-complexity energyefficient resource allocation, etc.) in this book. Due to the high mobility and low latency requirements of 5G wireless communications, this book discusses how to deal with the imperfect CSI. It also discusses how to deal with e.g., throughput maximization, outage probabilities maximization and guarantee, energy efficiency, physical-layer security issues with feedback channel capacity constraints, in order to characterize and understand the applications of practical scenes. This book will target professionals & researchers working in the fields of Wireless Communications and Networking, Resource Allocation and Transmissions. Advanced-level students in electrical engineering and computer science will also find this book useful as a secondary textbook.
Author: Sili Lu Publisher: ISBN: Category : Algorithms Languages : en Pages : 196
Book Description
Orthogonal frequency-division multiplexing (OFDM) has gained an increased popularity over the last few years and has been adopted as the modulation scheme of choice for beyond 3G mobile communication systems. This is mainly due to its high robustness to time dispersion effects and its low implementation complexity. DVB-H is the latest development within the set of Digital Video Broadcasting (DVB) standards that use OFDM as a modulation scheme. DVB-H is required to operate under high mobility conditions resulting in significant Inter-Carrier Interference (ICI). Under these conditions, the conventional one-tap per subcarrier channel estimation and equalization scheme is suboptimal since it does not account for ICI effects due to channel time-variation within an OFDM symbol. To mitigate ICI, we propose in this dissertation a simplified hybrid frequency/time-domain channel estimation algorithm. In addition, we design a reduced-complexity Q -tap frequency-domain equalizer (FEQ) and enhance its performance by integrating it with joint channel and data estimation and an ICI-mitigating pilot/data placement scheme. We also investigate differential OFDM detection as a low-complexity alternative for coherent detection and test its performance in the presence of Doppler for DVB-H system. Furthermore, we extend our approach to multiple-input multiple-out (MIMO) OFDM systems. We design a novel embedded space-frequency block code (SFBC)-OFDM scheme that performs well under high Doppler. We also propose a novel standard-conformable Cyclic Delay Diversity (CDD) scheme and its associated channel estimation scheme for comb-type OFDM transmissions, which achieves the Cramer-Rao lower bound on channel estimation mean square error.
Author: Adarsh Narasimhamurthy Publisher: Morgan & Claypool Publishers ISBN: 1598297023 Category : Technology & Engineering Languages : en Pages : 78
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: Publisher: ISBN: Category : Languages : en Pages :
Book Description
In a typical orthogonal frequency division multiplexing (OFDM) broadband wireless communication system, a guard interval using cyclic prefix is inserted to avoid the inter-symbol interference and the inter-carrier interference. This guard interval is required to be at least equal to, or longer than the maximum channel delay spread. This method is very simple, but it reduces the transmission efficiency. This efficiency is very low in the communication systems, which inhibit a long channel delay spread with a small number of sub-carriers such as the IEEE 802.11a wireless LAN (WLAN). To increase the transmission efficiency, it is usual that a time domain equalizer (TEQ) is included in an OFDM system to shorten the effective channel impulse response within the guard interval. There are many TEQ algorithms developed for the low rate OFDM applications such as asymmetrical digital subscriber line (ADSL). The drawback of these algorithms is a high computational load. Most of the popular TEQ algorithms are not suitable for the IEEE 802.11a system, a high data rate wireless LAN based on the OFDM technique. In this thesis, a TEQ algorithm based on the minimum mean square error criterion is investigated for the high rate IEEE 802.11a system. This algorithm has a comparatively reduced computational complexity for practical use in the high data rate OFDM systems. In forming the model to design the TEQ, a reduced convolution matrix is exploited to lower the computational complexity. Mathematical analysis and simulation results are provided to show the validity and the advantages of the algorithm. In particular, it is shown that a high performance gain at a data rate of 54Mbps can be obtained with a moderate order of TEQ finite impulse response (FIR) filter. The algorithm is implemented in a field programmable gate array (FPGA). The characteristics and regularities between the elements in matrices are further exploited to reduce the hardware complexity in the matrix multiplication.
Author: Ahmad R.S. Bahai Publisher: Springer Science & Business Media ISBN: 030646974X Category : Technology & Engineering Languages : en Pages : 224
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.
Author: Yufei Jiang Publisher: Springer ISBN: 9783319249827 Category : Computers Languages : en Pages : 0
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: Miaowen Wen Publisher: Springer Nature ISBN: 9811594074 Category : Technology & Engineering Languages : en Pages : 182
Book Description
Thanks to their considerable advantages, index modulation and orthogonal frequency division multiplexing (OFDM) are considered to be promising candidates for future wireless communications. This book focuses on the index modulation techniques for OFDM communications systems, which allow information to be conveyed not only via constellation symbols, but also by the indices of various transmission entities in OFDM systems, such as signal constellations, spreading codes, and pilots. The book discusses representative transmitter and receiver designs, optimization and performance analysis of index modulation based on various transmission entities. It first introduces readers to constellation-based index modulation via a combinatorial approach, including the classical index modulation scheme and two embodiments of information-guided precoding for OFDM systems. It further discusses constellation-based index modulation via a permutational approach, including the basic, generalized, and diversity-enhancing forms. It then describes how the spreading code is used to design an index modulated spread spectrum for OFDM systems, and the extensions to multi-code and multi-user scenarios. In addition it explores information guided pilot insertion for OFDM systems, followed by applications to carrier phase tracking and channel estimation. Lastly, the book highlights a number of open problems and discusses future research directions in the general field of index modulation. Intended for professionals and researchers in the field of wireless communications, this book is also a valuable resource for advanced-level electrical engineering and computer science students.
Author: Yihai Zhang Publisher: ISBN: Category : Languages : en Pages :
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: Adibi, Sasan Publisher: IGI Global ISBN: 1615206752 Category : Business & Economics Languages : en Pages : 836
Book Description
Fourth-Generation Wireless Networks: Applications and Innovations presents a comprehensive collection of recent findings in access technologies useful in the architecture of wireless networks.
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Author: Chen Chen
Author: Sili Lu
Author: Adarsh Narasimhamurthy
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Author: Ahmad R.S. Bahai
Author: Yufei Jiang
Author: Miaowen Wen
Author: Yihai Zhang
Author: Adibi, Sasan