Channel estimation techniques based on pilot arrangement in OFDM systems
TL;DR: This work has implemented a decision feedback equalizer for all sub-channels followed by periodic block-type pilots and compared the performances of all schemes by measuring bit error rates with 16QAM, QPSK, DQPSK and BPSK as modulation schemes, and multipath Rayleigh fading and AR based fading channels as channel models.
Abstract: Channel estimation techniques for OFDM systems based on a pilot arrangement are investigated. Channel estimation based on a comb type pilot arrangement is studied through different algorithms for both estimating the channel at pilot frequencies and interpolating the channel. Channel estimation at pilot frequencies is based on LS and LMS methods while channel interpolation is done using linear interpolation, second order interpolation, low-pass interpolation, spline cubic interpolation, and time domain interpolation. Time-domain interpolation is obtained by passing to the time domain by means of IDFT (inverse discrete Fourier transform), zero padding and going back to the frequency domain by DFT (discrete Fourier transform). In addition, channel estimation based on a block type pilot arrangement is performed by sending pilots in every sub-channel and using this estimation for a specific number of following symbols. We have also implemented a decision feedback equalizer for all sub-channels followed by periodic block-type pilots. We have compared the performances of all schemes by measuring bit error rates with 16QAM, QPSK, DQPSK and BPSK as modulation schemes, and multipath Rayleigh fading and AR based fading channels as channel models.
Citations
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TL;DR: This paper addresses basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques.
Abstract: Orthogonal frequency-division multiplexing (OFDM) effectively mitigates intersymbol interference (ISI) caused by the delay spread of wireless channels. Therefore, it has been used in many wireless systems and adopted by various standards. In this paper, we present a comprehensive survey on OFDM for wireless communications. We address basic OFDM and related modulations, as well as techniques to improve the performance of OFDM for wireless communications, including channel estimation and signal detection, time- and frequency-offset estimation and correction, peak-to-average power ratio reduction, and multiple-input-multiple-output (MIMO) techniques. We also describe the applications of OFDM in current systems and standards.
915 citations
Cites background from "Channel estimation techniques based..."
...Two of the simplest ways are piecewise constant and linear interpolation [2], [64]....
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...If the statistics of channel variation either in the frequency domain (PDP) or in the time domain (Doppler spectrum) are known a priori, a high-order polynomial can be applied to accurately fit wireless channels [64], [65]....
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Patent•
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TL;DR: In this article, a multiple-access MIMO WLAN system that employs MIMI, OFDM, and TDD was proposed, which employs a channel structure with a number of configurable transport channels, supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities.
Abstract: A multiple-access MIMO WLAN system that employs MIMO, OFDM, and TDD. The system (1) uses a channel structure with a number of configurable transport channels, (2) supports multiple rates and transmission modes, which are configurable based on channel conditions and user terminal capabilities, (3) employs a pilot structure with several types of pilot (e.g., beacon, MIMO, steered reference, and carrier pilots) for different functions, (4) implements rate, timing, and power control loops for proper system operation, and (5) employs random access for system access by the user terminals, fast acknowledgment, and quick resource assignments. Calibration may be performed to account for differences in the frequency responses of transmit/receive chains at the access point and user terminals. The spatial processing may then be simplified by taking advantage of the reciprocal nature of the downlink and uplink and the calibration.
759 citations
TL;DR: Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system using the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel.
Abstract: Techniques are described for efficiently estimating and compensating for the effects of a communication channel in a multi-carrier wireless communication system. The techniques exploit the fact that the transmitted symbols are drawn from a finite-alphabet to efficiently estimate the propagation channel for multi-carrier communication systems, such systems using OFDM modulation. A transmitter transmits data through a communication channel according to the modulation format. A receiver includes a demodulator to demodulate the data and an estimator to estimate the channel based on the demodulated data. The channel estimator applies a power-law operation to the demodulated data to identify the channel. The techniques can be used in both blind and semi-blind modes of channel estimation.
604 citations
Cites background or methods from "Channel estimation techniques based..."
...Indeed, if the system can tolerate more latency, then the channel estimation for non-training OFDM symbols can be improved by higher order polynomials [66, 84, 85]....
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...Fourier [31, 84, 101, 104, 105], Hadamard [106, 107], Discrete Cosine [108, 109], Karhunen-Loeve Transform KLT [110], and 2-D Fourier Transformation [111] are few to name....
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...Piecewise Linear Interpolation — Two of the simplest ways of interpolation are the use of piecewise constant [86] and linear interpolation [22, 84, 87, 88]....
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...In the spline interpolation, basis function of some orders or Beizer curve are defined over a group of subcarriers [60, 84]....
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10 Feb 2011
TL;DR: An overview of the existing vehicular channel measurements in a variety of important environments, and the observed channel characteristics (such as delay spreads and Doppler spreads) therein, is provided.
Abstract: To make transportation safer, more efficient, and less harmful to the environment, traffic telematics services are currently being intensely investigated and developed. Such services require dependable wireless vehicle-to-infrastructure and vehicle-to-vehicle communications providing robust connectivity at moderate data rates. The development of such dependable vehicular communication systems and standards requires accurate models of the propagation channel in all relevant environments and scenarios. Key characteristics of vehicular channels are shadowing by other vehicles, high Doppler shifts, and inherent nonstationarity. All have major impact on the data packet transmission reliability and latency. This paper provides an overview of the existing vehicular channel measurements in a variety of important environments, and the observed channel characteristics (such as delay spreads and Doppler spreads) therein. We briefly discuss the available vehicular channel models and their respective merits and deficiencies. Finally, we discuss the implications for wireless system design with a strong focus on IEEE 802.11p. On the road towards a dependable vehicular network, room for improvements in coverage, reliability, scalability, and delay are highlighted, calling for evolutionary improvements in the IEEE 802.11p standard. Multiple antennas at the onboard units and roadside units are recommended to exploit spatial diversity for increased diversity and reliability. Evolutionary improvements in the physical (PHY) and medium access control (MAC) layers are required to yield dependable systems. Extensive references are provided.
454 citations
Cites methods from "Channel estimation techniques based..."
...The block least square (B-LS) estimator [98]–[100] is defined in [97, (1)]....
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...These techniques have been used in other communication systems with good results [98]–[100], [102], [103]....
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TL;DR: The estimation error shows that the presented algorithm is comparable to the minimum mean square error (MMSE) with full knowledge of the channel statistics, and it is better than an approximation to linear MMSE.
Abstract: In this letter, we present a deep learning algorithm for channel estimation in communication systems. We consider the time–frequency response of a fast fading communication channel as a 2D image. The aim is to find the unknown values of the channel response using some known values at the pilot locations. To this end, a general pipeline using deep image processing techniques, image super-resolution (SR), and image restoration (IR) is proposed. This scheme considers the pilot values, altogether, as a low-resolution image and uses an SR network cascaded with a denoising IR network to estimate the channel. Moreover, the implementation of the proposed pipeline is presented. The estimation error shows that the presented algorithm is comparable to the minimum mean square error (MMSE) with full knowledge of the channel statistics, and it is better than an approximation to linear MMSE. The results confirm that this pipeline can be used efficiently in channel estimation.
373 citations
Cites background from "Channel estimation techniques based..."
...To estimate the channel, specifically in the channels with fading, the time domain response is divided into subframes H = {h[1],h[2], ....
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...Depending on these pilot arrangements, three different structures can be considered: block-type, comb-type and lattice-type [1], [2]....
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References
More filters
Book•
01 Jan 1989
TL;DR: In this paper, the authors provide a thorough treatment of the fundamental theorems and properties of discrete-time linear systems, filtering, sampling, and discrete time Fourier analysis.
Abstract: For senior/graduate-level courses in Discrete-Time Signal Processing. THE definitive, authoritative text on DSP -- ideal for those with an introductory-level knowledge of signals and systems. Written by prominent, DSP pioneers, it provides thorough treatment of the fundamental theorems and properties of discrete-time linear systems, filtering, sampling, and discrete-time Fourier Analysis. By focusing on the general and universal concepts in discrete-time signal processing, it remains vital and relevant to the new challenges arising in the field --without limiting itself to specific technologies with relatively short life spans.
10,388 citations
TL;DR: The analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel using the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel is discussed.
Abstract: This paper discusses the analysis and simulation of a technique for combating the effects of multipath propagation and cochannel interference on a narrow-band digital mobile channel. This system uses the discrete Fourier transform to orthogonally frequency multiplex many narrow subchannels, each signaling at a very low rate, into one high-rate channel. When this technique is used with pilot-based correction, the effects of flat Rayleigh fading can be reduced significantly. An improvement in signal-to-interference ratio of 6 dB can be obtained over the bursty Rayleigh channel. In addition, with each subchannel signaling at a low rate, this technique can provide added protection against delay spread. To enhance the behavior of the technique in a heavily frequency-selective environment, interpolated pilots are used. A frequency offset reference scheme is employed for the pilots to improve protection against cochannel interference.
2,627 citations
"Channel estimation techniques based..." refers methods in this paper
...The linear interpolation method is shown to perform better than the piecewise-constant interpolation in [7]....
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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
"Channel estimation techniques based..." refers background or methods in this paper
...The MMSE estimate has been shown to give 10–15 dB gain in signal-to-noise ratio (SNR) for the same mean square error of channel estimation over LS estimate [2]....
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28 Apr 1996
TL;DR: The theory of optimal rank-reduction is applied to linear minimum mean-squared error (LMMSE) estimators and it is shown that these estimators, when using a fixed design, are robust to changes in channel correlation and signal-to-noise ratio (SNR).
Abstract: We present and analyze low-rank channel estimators for orthogonal frequency-division multiplexing (OFDM) systems using the frequency correlation of the channel. Low-rank approximations based on the discrete Fourier transform (DFT) have been proposed, but these suffer from poor performance when the channel is not sample spaced. We apply the theory of optimal rank-reduction to linear minimum mean-squared error (LMMSE) estimators and show that these estimators, when using a fixed design, are robust to changes in channel correlation and signal-to-noise ratio (SNR). The performance is presented in terms of uncoded symbol-error rate (SER) for a system using 16-quadrature amplitude modulation (QAM).
1,566 citations
"Channel estimation techniques based..." refers methods in this paper
...The estimation of the channel for this block-type pilot arrangement can be based on Least Square (LS) or Minimum Mean-Square (MMSE)....
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Book•
14 May 1999
TL;DR: Mobile Radio Communications, Second Edition as discussed by the authors is a reference work for second and third-generation mobile radio communications that provides a comprehensive overview of the current state-of-the-art.
Abstract: From the Publisher:
Mobile radio communications technology has progressed rapidly and it is now capable of the transmission of voice, data and image signals. This new edition explains the latest techniques employed in second and third generation systems. A comprehensive all-in-one mobile communication reference work, Mobile Radio Communications, Second Edition reflects the current state-of-the-art by featuring expanded and updated sections on voice compression techniques, interleaving and channel coding methods, quaternary frequency shift keying, continuous phase modulation methods, Viterbi equalisation and slow frequency hopping as well as extended coverage of the GSM system; and three new chapters on wireless multimedia, third generation systems and on WATM respectively. As in the first edition, this edition continues to cover important topics such as radio propagation, multiple access methods and, on a higher level, cordless telecommunications and teletraffic issues. This book will prove invaluable to mobile communication engineers, designers, researchers and students in the design, operation and research of second and third generation systems and wireless LANs.
871 citations