Pilot sequence design for improving OFDM channel estimation in the presence of CFO
18 Jul 2010-pp 1-5
TL;DR: The proposed procedure completely eliminates the effect of the ICI on the channel estimate and both analytical and computer simulation results demonstrate the superiority of the proposed scheme over the mLS estimator.
Abstract: We consider the design of pilot sequences for channel estimation in the presence of carrier frequency offset (CFO) in systems that employ orthogonal frequency division multiplexing (OFDM). The CFO introduces intercarrier interference (ICI) which degrades the accuracy of the channel estimation. To minimize this effect, we solve for the pilot sequence that minimizes the mean square error of the modified least squares (mLS) channel estimator. The transmission of this sequence results in high peak-to-average power ratio (PAPR) of the OFDM signal. To solve this problem, we first introduce a new estimator as an alternative to the mLS estimator. We then design a low PAPR pilot sequence tailored to this new estimator. We show that the proposed procedure completely eliminates the effect of the ICI on the channel estimate. Both analytical and computer simulation results demonstrate the superiority of the proposed scheme over the mLS estimator.
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TL;DR: A novel modified LS channel estimation method is proposed, which is based on noise reduction procedure to improve the channel estimation accuracy, and the simulation results demonstrate that comparing to LSChannel estimation algorithm, LMMSE algorithm and the proposed modified LS algorithm provide better performances.
5 citations
Cites methods from "Pilot sequence design for improving..."
...efficiency, simple and efficient implementation by the application of the fast Fourier transform(FFT) and the inverse fast Fourier transform(IFFT), reduction of inter symbol interference(ISI) by inserting cyclic prefix(CP), and robustness to multi-path fading and delay[1-3]....
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TL;DR: The authors introduce a new estimator as an alternative to the mLS estimator and design a low PAPR pilot sequences tailored to this new estimators, showing that the proposed procedure completely eliminates the effect of the ICI on the channel estimate.
Abstract: The authors consider the design of pilot sequences for channel estimation in the presence of carrier frequency offset (CFO) in systems that employ orthogonal frequency division multiplexing (OFDM). The CFO introduces intercarrier interference (ICI) which degrades the accuracy of the channel estimation. In order to minimise this effect, the authors design pilot sequence that minimises the mean square error (MSE) of the modified least squares (mLS) channel estimator. Since the identical pilot sequence, which minimises this MSE, has high peak-to-average power ratio of the OFDM signal, an alternative approach is proposed for channel estimation. The authors first introduce a new estimator as an alternative to the mLS estimator and design a low PAPR pilot sequences tailored to this new estimator. They show that the proposed procedure completely eliminates the effect of the ICI on the channel estimate. They then extend their design of pilot sequences for realistic sparse channels. Both analytical and computer simulation results presented in this study demonstrate the superiority of the proposed approach over conventional methods for channel estimation in the presence of ICI.
4 citations
TL;DR: In this article, the effect of power amplifier nonlinearity on the uplink and downlink sum-rate of CF mMIMO systems was studied in the presence of hardware impairments.
Abstract: Cell free (CF) massive multiple input multiple output (mMIMO) has been suggested as a key solution to meet the high data rate demands of future wireless communications. Studying the performance of these systems in practical scenarios such as in the presence of hardware impairments is of vital importance. In this paper, we study the effect of power amplifier non-linearity on the uplink and downlink sum-rate of CF mMIMO systems. We derive closed form expressions for the uplink and downlink achievable sum-rates of orthogonal frequency division multiplexing (OFDM) based CF mMIMO systems. Our results show that in the uplink the sum-rate does not increase unlimitedly as the number of access points (AP) increases, being upper bounded, contrarily to the ideal linear case. In fact, the rate of each user is limited by the distortion signal of its power amplifier. However, in the downlink, the sum-rate of the system with non-linear power amplifiers is not bounded and increases unlimitedly with the number of APs. Our results also indicate that for the same signal to distortion ratio (SDR) at the power amplifier output or the same normalized saturation level of the power amplifiers, the relative downlink sum-rate degradation is lower than the relative uplink sum-rate degradation (both with respect to their corresponding values in the ideal linear case). In fact, our results confirm that the user side power amplifier non-linearity has higher impact on the system performance than the power amplifier non-linearity on the AP antennas.
1 citations
References
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Book•
31 Dec 1999
TL;DR: In this paper, the authors present a comprehensive introduction to OFDM for wireless broadband multimedia communications and provide design guidelines to maximize the benefits of this important new technology, including modulation and coding, synchronization, and channel estimation.
Abstract: From the Book:
The manifestations of the mode of goodness can be experienced when all the gates of the body are illuminated by knowledge
The Bhagavad Gita (14.11)
During the joint supervision of a Master's thesis "The Peak-to-Average Power Ratio of OFDM," of Arnout de Wild from Delft University of Technology, The Netherlands, we realized that there was a shortage of technical information on orthogonal frequency division multiplexing (OFDM) in a single reference. Therefore, we decided to write a comprehensive introduction to OFDM. This is the first book to give a broad treatment to OFDM for mobile multimedia communications. Until now, no such book was available in the market. We have attempted to fill this gap in the literature.
Currently, OFDM is of great interest by the researchers in the Universities and research laboratories all over the world. OFDM has already been accepted for the new wireless local area network standards from IEEE 802.11, High Performance Local Area Network type 2 (HIPERLAN/2) and Mobile Multimedia Access Communication (MMAC) Systems. Also, it is expected to be used for the wireless broadband multimedia communications.
OFDM for Wireless Multimedia Communications is the first book to take a comprehensive look at OFDM, providing the design guidelines one needs to maximize benefits from this important new technology. The book gives engineers a solid base for assessing the performance of wireless OFDM systems. It describes the new OFDM-based wireless LAN standards; examines the basics of direct-sequence and frequency-hopping CDMA, helpful in understanding combinations of OFDM and CDMA. It also looks at applications of OFDM, includingdigital audio and video broadcasting, and wireless ATM. Loaded with essential figures and equations, it is a must-have for practicing communications engineers, researchers, academics, and students of communications technology.
Chapter 1 presents a general introduction to wireless broadband multimedia communication systems (WBMCS), multipath propagation, and the history of OFDM. A part of this chapter is based on the contributions of Luis Correia from the Technical University of Lisbon, Portugal, Anand Raghawa Prasad from Lucent Technologies, and Hiroshi Harada from the Communications Research Laboratory, Ministry of Posts and Telecommunications, Yokosuka, Japan.
Chapters 2 to 5 deal with the basic knowledge of OFDM including modulation and coding, synchronization, and channel estimation, that every post-graduate student as well as practicing engineers must learn. Chapter 2 contains contributions of Rob Kopmeiners from Lucent Technologies on the FFT design.
Chapter 6 describes the peak-to-average power problem, as well as several solutions to it. It is partly based on the contribution of Arnout de Wild.
Basic principles of CDMA are discussed in Chapter 7 to understand multi carrier CDMA and frequency-hopping OFDMA, which are described in Chapters 8 and 9. Chapter 8 is based on the research contributions from Shinsuke Hara from the University of Osaka, Japan, a postdoctoral student at Delft University of Technology during 1995-96, Chapter 9 is based on a UMTS proposal, with main contributions of Ralf Bohnke from Sony, Germany, David Bhatoolaul and Magnus Sandell from Lucent Technologies, Matthias Wahlquist from Telia Research, Sweden, and Jan-Jaap van de Beek from Lulea University, Sweden.
Chapter 10 was written from the viewpoint of top technocrats from industries, government departments, and policy-making bodies. It describes several applications of OFDM, with the main focus on wireless ATM in the Magic WAND project, and the new wireless LAN standards for the 5 GHz band from IEEE 802.11, HIPERLAN/2 and MMAC. It is partly based on contributions from Geert Awater from Lucent Technologies, and Masahiro Morikura and Hitoshi Takanashi from NTT in Japan and California, respectively.
We have tried our best to make each chapter quite complete in itself This book will help generate many new research problems and solutions for future mobile multimedia communications. We cannot claim that this book is errorless. Any remarks to improve the text and correct any errors would be highly appreciated.
4,020 citations
"Pilot sequence design for improving..." refers background in this paper
...For the case X0 = IN , x = [1, 1, · · · , 1] T and, b = 1 N W x = [1, 0, 0, · · · , 0] , the PAPR is given by PAPRI = 1 (1/N)[1] = N, and hence identical pilots are not desirable in practical OFDM systems [4]....
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...However, OFDM is highly vulnerable to carrier frequency offset (CFO) due to oscillator mismatch, Doppler frequency spread and phase noise [1]....
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...Orthogonal frequency division multiplexing (OFDM) has received considerable attention in modern broadband communication systems owing to its immunity to frequencyselective fading, along with high bit rate support [1]....
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TL;DR: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered and the degradation of the bit error rate is evaluated.
Abstract: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >
1,816 citations
"Pilot sequence design for improving..." refers background in this paper
...Consequently, CFO introduces intercarrier interference (ICI) among the subcarriers, which leads to high bit error rates (BER) [2]....
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25 Jul 1995
TL;DR: The authors present the MMSE and LS estimators and a method for modifications compromising between complexity and performance and the symbol error rate for a 18-QAM system is presented by means of simulation results.
Abstract: The use of multi-amplitude signaling schemes in wireless OFDM systems requires the tracking of the fading radio channel. The paper addresses channel estimation based on time-domain channel statistics. Using a general model for a slowly fading channel, the authors present the MMSE and LS estimators and a method for modifications compromising between complexity and performance. The symbol error rate for a 18-QAM system is presented by means of simulation results. Depending upon estimator complexity, up to 4 dB in SNR can be gained over the LS estimator.
1,647 citations
"Pilot sequence design for improving..." refers background or methods in this paper
...We first show the identical pilot sequence that minimizes the MSE of mLS estimator [5] is free from ICI....
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...(2) can be improved by replacing the last N − L values of ĥ with zeros [5]....
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...Such an estimator is called in [4][5] as the modified least squares (mLS) estimator....
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...The wireless channel can be estimated by employing the pilot-aided schemes outlined in [4][5], with the assumption of perfect CFO estimation at the receiver....
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...(1), the LS estimator [5] of h (assuming a perfect estimate CFO ǫ at the receiver) is obtained as...
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28 Dec 2009
TL;DR: Orthogonal Frequency Division Multiplexing for Wireless Communications is an edited volume with contributions by leading authorities in the subject of OFDM, providing a comprehensive introduction of the theory and practice ofOFDM.
Abstract: Orthogonal Frequency Division Multiplexing for Wireless Communications is an edited volume with contributions by leading authorities in the subject of OFDM. Its coverage consists of principles, important wireless topics (e.g. Synchronization, channel estimation, etc.) and techniques. Included is information for advancing wireless communication in a multipath environment with an emphasis on implementation of OFDM in base stations. Orthogonal Frequency Division Multiplexing for Wireless Communications provides a comprehensive introduction of the theory and practice of OFDM. Chapter 1, by G. Stber, briefly introduces the history of OFDM or multicarrier modulation and basic concepts of OFDM, Chapter 2, by Y. (G.) Li, presents design of OFDM systems for wireless communications, various impairments caused by wireless channels, and some other types of OFDM related modulation. Chapter 3 to Chapter 6 address different techniques to mitigate the impairments and to improve the performance of OFDM systems. Chapter 3, by J. Cioffi and L. Hoo, focuses on system optimization techniques, including channel partitioning, loading of parallel channels, and optimization through coding. Chapter 4, by S. Wilson and P. dling, addresses timing- and frequency-offset estimation in OFDM systems. It also briefly discusses sampling clock offset estimation and correction. Chapter 5, by Y. (G.) Li, deals with pilot aided and decision-directed channel estimation for OFDM systems. Chapter 6, by C. Tellambura and M. Friese, discusses various techniques to reduce the peak-to-average power ratio of OFDM signals. To facilitate the readers, extensive subject indices and references are given at the end of the book. Even though each chapter is written by different experts, symbols and notations in all chapters of the book are consistent.
453 citations
TL;DR: It is shown that the bit-error rate for an uncoded OFDM system with quadrature amplitude modulation (QAM) can be expressed by the sum of a few integrals, whose number depends on the constellation size.
Abstract: We introduce an analytical approach to evaluate the error probability of orthogonal frequency-division-multiplexing (OFDM) systems subject to carrier frequency offset (CFO) in frequency-selective channels, characterized by Rayleigh or Rician fading. By properly exploiting the Gaussian approximation of the intercarrier interference (ICI), we show that the bit-error rate (BER) for an uncoded OFDM system with quadrature amplitude modulation (QAM) can be expressed by the sum of a few integrals, whose number depends on the constellation size. Each integral can be evaluated numerically, or, in Rayleigh fading, by using a series expansion that involves generalized hypergeometric functions. Simulation results illustrate that the theoretical analysis is quite accurate, especially for Rayleigh channels, and also with nonlinear amplifiers.
212 citations
"Pilot sequence design for improving..." refers background in this paper
...Therefore, CFO is estimated and compensated [3] at the receiver to improve the overall system performance....
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