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Author: Md. Muktar Hossain
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659540608
Category :
Languages : en
Pages : 60
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Book Description
In this book the channel estimation techniques for OFDM systems based on Block Type Pilot arrangement are investigated. Finally, the DFT based channel estimation technique is performed which gives better performance over LS and MMSE based channel estimation.With same SNR, the BER of DFT based channel estimation is less than the BER of LS and MMSE based channel estimation. The MMSE estimator has good performance but high complexity. The LS estimator has low complexity, but its performance is not as good as that MMSE estimator basically at low SNR. Block Type Pilot arrangement is suitable for frequency-selective channels. For the fast-fading channels, however, it might incur too much overhead to track the channel variation by reducing the pilot symbol period.As the use of pilot symbols for channel estimation decrease the spectrum efficiency of the wireless communication systems, it will be beneficial if we can adaptively change the number of pilot tones depending on the channel condition through some feedback information.
Author: Md. Muktar Hossain
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659540608
Category :
Languages : en
Pages : 60
Get Book Here
Book Description
In this book the channel estimation techniques for OFDM systems based on Block Type Pilot arrangement are investigated. Finally, the DFT based channel estimation technique is performed which gives better performance over LS and MMSE based channel estimation.With same SNR, the BER of DFT based channel estimation is less than the BER of LS and MMSE based channel estimation. The MMSE estimator has good performance but high complexity. The LS estimator has low complexity, but its performance is not as good as that MMSE estimator basically at low SNR. Block Type Pilot arrangement is suitable for frequency-selective channels. For the fast-fading channels, however, it might incur too much overhead to track the channel variation by reducing the pilot symbol period.As the use of pilot symbols for channel estimation decrease the spectrum efficiency of the wireless communication systems, it will be beneficial if we can adaptively change the number of pilot tones depending on the channel condition through some feedback information.
Author: 廖芝青
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Author: Fei Wang
Publisher:
ISBN:
Category : Mobile communication systems
Languages : en
Pages : 81
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Book Description
Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technology in wireless environment, and can also be seen as a multi-carrier digital modulation or multi-carrier digital multiplexing technology. A large number of orthogonal sub-carriers are used to transmit information. OFDM system has high utilization of frequency spectrum and satisfactory capability of reducing multi-path inference. So, OFDM has been considered as one of the core technologies of 4th generation (4G) wireless communication system in the future. Channel estimation plays a very important role in OFDM system. As a research hotpot, many related algorithms have been presented these years, which can be generally separated into two methods, pilot-based channel estimation and blind channel estimation. Pilot-based channel estimation estimates the channel information by obtaining the impulse response from all sub-carriers by pilot. Compared with blind channel estimation, which uses statistical information of the received signals, pilot-based channel estimation is a practical and an effective method. This thesis is on the pilot-based channel estimation of OFDM system. Firstly, it introduces the basic principle and realization of OFDM system, and describes the system construction and model with summary of some key technologies, such as fast Fourier transform (FFT) and cyclic prefix (CP). We also analyze OFDM modulation in the frequency domain, and discusses some advantages and disadvantages of OFDM system. Next, a summary of multi-path and time varying statistical properties of general wireless channel of OFDM system are presented. This thesis also investigates principles and performances of the channel estimation methods, block type pilot and comb type pilot. In the arrangement of block type pilot, the performance of channel estimation is analyzed with estimators based on three different algorithms, least square (LS) algorithm, linear minimum mean square error (LMMSE) algorithm and singular value decomposition (SVD) algorithm. To use comb-type pilot arrangement, the thesis introduces three methods of interpolation: linear interpolation, second order interpolation and cubic spline interpolation. Finally, simulation results using Matlab are used to compare bit error rate (BER) performance of different modulation schemes and types of pilot.
Author: Jianjun Ran
Publisher: Cuvillier Verlag
ISBN: 3736926499
Category : Technology & Engineering
Languages : en
Pages : 162
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Book Description
The emerging wireless communication systems, such as cellular communications systems and wireless net-works, are changing the life style nowadays dramatically. The prospect of modern wireless communication systems is very attractive by declaring the ability of ubiquitous access to information with high-quality and high-speed service. The Orthogonal Frequency Division Multiplexing (OFDM) technique is one promising candidate for the $4^{th}$ generation wireless systems, due to its merits of high flexibility and low equalization complexity for wideband wireless communication applications. To further enhance the communication system capacity and reliability, multiple antenna techniques can be integrated into OFDM systems. As a preliminary step, the physical characteristics of wideband radio channels and the channel modeling issue are addressed. The channel capacity with multiple antennas is presented by considering both cases of ideal and practical estimated channel state information (CSI) in the system. The fundamentals of the OFDM transmission technique are introduced. With the OFDM transmission structu-re the frequency-selective wideband radio channel is decomposed into a set of parallel subcarriers, and each subcarrier can be treated as a flat-fading narrowband channel. Several Multiple-Input-Multiple-Output (MIMO) technologies are discussed, in the scope of subcarrier-based MIMO encoding and decoding within the MIMO-OFDM transceiver structure, i.\ e.\ integrate the MIMO signal processing algorithms into a wideband OFDM system, where each OFDM subcarrier is regarded individually as a narrowband flat-fading subsystem with the Discrete Fourier Transform (DFT) and Inverse Discrete Fou-rier Transform (IDFT). The simulation results and analysis are presented under various radio channel condi-tions with ideal CSI. For practical reasons, channel estimation is necessary for coherent-detection MIMO-OFDM systems. The Pilot-based Channel Estimation (PBCE) schemes are implemented to evaluate the system performance with the realistically estimated CSI. With estimated CSI for MIMO encoding/decoding and data symbol detection, the system performance is reasonably degraded. The system performance results with estimated CSI are presented, and the impact of channel estimation errors is analyzed. In order to ensure a reliable and flexible data transmission in MIMO-OFDM systems, the indicator-based link adaptation procedure is employed to optimize the system throughput by selecting a proper Transmission Mode (TM) according to the instantaneous channel conditions. The Transmission Mode Selection (TMS) procedure with two-dimensional (2D) indicators is developed. A set of indicator candidates and their appro-ximation functions are proposed. With the indicator simulation results and the proposed TMS procedure for MIMO-OFDM systems, the average system throughput results are illustrated for both the conventional link adaptation method and the proposed 2D indicator-based TMS approach. Finally, the general system performance results of MIMO-OFDM systems are summarized. Arguments and suggestions are further made on how to design a MIMO-OFDM system in various wideband wireless com-munication applications.
Author:
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Category :
Languages : en
Pages :
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Book Description
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.
Author: Mohamed Jalloh
Publisher:
ISBN:
Category :
Languages : en
Pages : 197
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Book Description
The age of wireless technologies and the associated convenience that portable wireless products and services provide, continues to drive the need for more advanced products and broadband wireless services that demand carefully selected spectrally efficient modulation schemes to support the desired higher data rates. The development of multicarrier systems has paved the way to meeting the system requirements and fulfilling these needs. Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique that has provided effective means for achieving high data rates and spectral efficiency requirements in wireless communication systems, while making use of relatively simple receiver designs. In wireless communications, one of the major implementation challenges is system sensitivity to synchronization issues, which is even more pronounced in multicarrier systems such as OFDM. The use of OFDM with a high number of subcarriers, to achieve the high data rates it provides, makes it more susceptible to these non-idealities such as phase noise. Another critically limiting factor of system performance is the introduction of channel estimation errors as a consequence of imperfect channel estimation at the receiver. Accurate channel estimates are very essential in ensuring correct detection of the transmitted signal at the receiver. A thorough understanding of system operation therefore requires a detailed analysis of the effects of all the impairments. This dissertation addresses these system impairments by investigating the effects analytically on OFDM systems, deriving bit error rate (BER) expressions for systems that employ a single antenna at both the transmitter and receiver. The investigation is extended to also include OFDM systems that employ multi-antenna configurations at the receiver followed by a similar multi-antenna configuration at the transmitter. The impact of these negative effects is further investigated when applied to a practical system, comparing the analytical results with simulations that makes use of system parameters of the IEEE 802.16 standards.
Author: Sunil Dutt Purohit
Publisher: Springer Nature
ISBN: 9811550778
Category : Technology & Engineering
Languages : en
Pages : 669
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Book Description
This book offers a collection of high-quality peer-reviewed research papers presented at the Second International Conference on Communication and Computational Technologies (ICCCT 2019), held at Rajasthan Institute of Engineering and Technology, Jaipur, Rajasthan, India, on 30–31 August 2019. In contributions prepared by researchers from academia and industry alike, the book discusses a wide variety of industrial, engineering and scientific applications of emerging techniques.
Author: Bios Diallo
Publisher:
ISBN:
Category : Technology
Languages : en
Pages :
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Book Description
DFT Based Channel Estimation Methods for MIMO-OFDM Systems.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
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
