Author: Xiangguo Tang
Publisher:
ISBN:
Category :
Languages : en
Pages : 266

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Author: Chandra Sekhar Bontu
Publisher:
ISBN:
Category :
Languages : en
Pages : 424

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Author: Gregory E. Bottomley
Publisher: John Wiley & Sons
ISBN: 1118105273
Category : Technology & Engineering
Languages : en
Pages : 192

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Book Description
The most thorough, up-to-date reference on channel equalization—from basic concepts to complex modeling techniques In today's instant-access society, a high premium is placed on information that can be stored and communicated effectively. As a result, storage densities and communications rates are being pushed to capacity, causing information symbols to interfere with one another. To help unclog pathways for the clearer conveyance of information, this book offers in-depth discussion of the significant contributions and future adaptability of channel equalization and a set of approaches for solving the problem of intersymbol interference (ISI). Chapter explorations in Channel Equalization include: Channel equalization topics presented with incremental learning methodology—from the very fundamental concept to more advanced mathematical knowledge Coverage of technology used in second-, third- and fourth-generation cellular communication systems A set of homework problems that reinforce concepts discussed in the book Tutorial explanations of recent developments currently captured in IEEE technical journals Unlike existing digital communications books that devote cursory attention to channel equalization, this invaluable guide addresses a crucial need by focusing solely on the background, current state, and future direction of this increasingly important technology. A unique mix of basic concepts and complex frameworks for delivering digitized data make Channel Equalization a valuable reference for all practicing wireless communication engineers and students dealing with the pressing demands of the information age.

Author:
Publisher:
ISBN:
Category : Orthogonal frequency division multiplexing
Languages : en
Pages : 212

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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: Wei Zhang Zhang
Publisher:
ISBN:
Category : Integrated circuits
Languages : en
Pages :

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Book Description
Receiver design, especially equalizer design, in communications is a major concern in both academia and industry. It is a problem with both theoretical challenges and severe implementation hurdles. While much research has been focused on reducing complexity for optimal or near-optimal schemes, it is still common practice in industry to use simple techniques (such as linear equalization) that are generally significantly inferior. Although digital signal processing (DSP) technologies have been applied to wireless communications to enhance the throughput, the users' demands for more data and higher rate have revealed new challenges. For example, to collect the diversity and combat fading channels, in addition to the transmitter designs that enable the diversity, we also require the receiver to be able to collect the prepared diversity. Most wireless transmissions can be modeled as a linear block transmission system. Given a linear block transmission model assumption, maximum likelihood equalizers (MLEs) or near-ML decoders have been adopted at the receiver to collect diversity which is an important metric for performance, but these decoders exhibit high complexity. To reduce the decoding complexity, low-complexity equalizers, such as linear equalizers (LEs) and decision feedback equalizers (DFEs) are often adopted. These methods, however, may not utilize the diversity enabled by the transmitter and as a result have degraded performance compared to MLEs. In this dissertation, we will present efficient receiver designs that achieve low bit-error-rate (BER), high mutual information, and low decoding complexity. Our approach is to first investigate the error performance and mutual information of existing low-complexity equalizers to reveal the fundamental condition to achieve full diversity with LEs. We show that the fundamental condition for LEs to collect the same (outage) diversity as MLE is that the channels need to be constrained within a certain distance from orthogonality. The orthogonality deficiency (od) is adopted to quantify the distance of channels to orthogonality while other existing metrics are also introduced and compared. To meet the fundamental condition and achieve full diversity, a hybrid equalizer framework is proposed. The performance-complexity trade-off of hybrid equalizers is quantified by deriving the distribution of od. Another approach is to apply lattice reduction (LR) techniques to improve the "quality" of channel matrices. We present two widely adopted LR methods in wireless communications, the Lenstra-Lenstra-Lovasz (LLL) algorithm [51] and Seysen's algorithm (SA), by providing detailed descriptions and pseudo codes. The properties of output matrices of the LLL algorithm and SA are also quantified. Furthermore, other LR algorithms are also briefly introduced. After introducing LR algorithms, we show how to adopt them into the wireless communication decoding process by presenting LR-aided hard-output detectors and LR-aided soft-output detectors for coded systems, respectively. We also analyze the performance of proposed efficient receivers from the perspective of diversity, mutual information, and complexity. We prove that LR techniques help to restore the diversity of low-complexity equalizers without increasing the complexity significantly. When it comes to practical systems and simulation tool, e.g., MATLAB, only finite bits are adopted to represent numbers. Therefore, we revisit the diversity analysis for finite-bit represented systems. We illustrate that the diversity of MLE for systems with finite-bit representation is determined by the number of non-vanishing eigenvalues. It is also shown that although theoretically LR-aided detectors collect the same diversity as MLE in the real/complex field, it may show different diversity orders when finite-bit representation exists. Finally, the VLSI implementation of the complex LLL algorithms is provided to verify the practicality of our proposed designs.

Author: Andreas F. Molisch
Publisher: Prentice Hall
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 584

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Book Description
This proposed book gives a comprehensive desciption of the various approaches to realize wireless wideband transmission systems, and how those approaches perform in different types of mobile radio channels. The covered topics include: 1) unequalized systems; 2) equalizers for TDMA/FDMA systems; 3) OFDM, and 4) Rake receivers for CDMA.

Author: Giorgio A. Vitetta
Publisher: John Wiley & Sons
ISBN: 1118576608
Category : Technology & Engineering
Languages : en
Pages : 849

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Book Description
This book introduces the theoretical elements at the basis of various classes of algorithms commonly employed in the physical layer (and, in part, in MAC layer) of wireless communications systems. It focuses on single user systems, so ignoring multiple access techniques. Moreover, emphasis is put on single-input single-output (SISO) systems, although some relevant topics about multiple-input multiple-output (MIMO) systems are also illustrated. Comprehensive wireless specific guide to algorithmic techniques Provides a detailed analysis of channel equalization and channel coding for wireless applications Unique conceptual approach focusing in single user systems Covers algebraic decoding, modulation techniques, channel coding and channel equalisation

Author: Franz Hlawatsch
Publisher: Academic Press
ISBN: 0080922724
Category : Technology & Engineering
Languages : en
Pages : 457

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Book Description
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

Author: Thomas Alexander Drumright
Publisher:
ISBN:
Category :
Languages : en
Pages : 256

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Author: Hermanus Carel Myburgh
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description