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Compressive and Noncompressive Power Spectral Density Estimation from Periodic Nonuniform Samples  [PDF]
Michael A. Lexa,Mike E. Davies,John S. Thompson
Mathematics , 2011,
Abstract: This paper presents a novel power spectral density estimation technique for band-limited, wide-sense stationary signals from sub-Nyquist sampled data. The technique employs multi-coset sampling and incorporates the advantages of compressed sensing (CS) when the power spectrum is sparse, but applies to sparse and nonsparse power spectra alike. The estimates are consistent piecewise constant approximations whose resolutions (width of the piecewise constant segments) are controlled by the periodicity of the multi-coset sampling. We show that compressive estimates exhibit better tradeoffs among the estimator's resolution, system complexity, and average sampling rate compared to their noncompressive counterparts. For suitable sampling patterns, noncompressive estimates are obtained as least squares solutions. Because of the non-negativity of power spectra, compressive estimates can be computed by seeking non-negative least squares solutions (provided appropriate sampling patterns exist) instead of using standard CS recovery algorithms. This flexibility suggests a reduction in computational overhead for systems estimating both sparse and nonsparse power spectra because one algorithm can be used to compute both compressive and noncompressive estimates.
Performance Improvement of MIMO OFDM Systems through Channel Estimation  [PDF]
B Shoba,K Jayanthi
International Journal of Wireless & Mobile Networks , 2012,
Abstract: A brief overview of MIMO-OFDM system design has been discussed and its key techniques areintroduced. It also focuses on OFDM-based air interface, spatial channel modelling, transceiver design,channel estimation and minimizing the BER ratio by modifying the Maximum Likelihood function throughchannel estimation.
Joint Iterative Channel Estimation and Detection for OFDM/OQAM System

Hu Su Wu Gang Xiao Yue Li Shao-qian,

电子与信息学报 , 2009,
Abstract: Compared with OFDM system with Cyclic Prefix (CP-OFDM) which satisfies strictly complex field orthogonality, OFDM/Offset QAM system (OFDM/OQAM) only satisfies the real field orthogonality. Therefore, in present of multipath fading channel, the Inter Symbol Interference (ISI) and Inter Carrier Interference (ICI) always exist in the OFDM/OQAM system if utilizing the conventional preamble based channel estimation method for CP-OFDM system. In this paper, a joint iterative channel estimation and detection is proposed for OFDM/OQAM system. The proposed method exchanges the information between channel estimator and demodulator to remove the ISI and ICI effectively. Simulation results demonstrate that as the number of iterative time increasing, BER performance of the joint iterative channel estimation and detection method is approximately close to perfect channel estimation.
Compressive Channel Estimation for OFDM Cooperation Networks  [cached]
Aihua Zhang,Guan Gui,Shouyi Yang
Research Journal of Applied Sciences, Engineering and Technology , 2012,
Abstract: In this study, we study compressive channel estimation for Orthogonal Frequency Division Multiplexing (OFDM) modulated Amplify-and-Forward (AF) relay networks. Based upon the mathematical channel model of P2P and sparseness measure function, by using Monte-Carlo runs, we show that the OFDM cooperation convoluted channels also exhibit sparsity. In this study, we propose two compressive channel estimation methods to exploit the inherent sparse structure in multipath fading channels of OFDM cooperation networks with Amplify-and-Forward (AF) relays, Simulation results demonstrate that the proposed compressive channel estimation methods provide significant improvement in mean square error (MSE) performance compared with the conventional channel estimation methods.
Vishal Ahlawat,Prachi Dahiya
International Journal of Electronics and Computer Science Engineering , 2012,
Abstract: Orthogonal frequency-division multiplexing (OFDM) has been employed in several current and future 4-thgeneration (4G) wireless standards. Frequency offsets in OFDM introduce intercarrier interference (ICI). Channel estimations are also required. This thesis focuses on the channel and frequency offset estimation for OFDMbased systems. For cooperative-relay OFDM with frequency offsets, where inter-relay interference (IRI) exists, channel estimation is developed. Optimal pilot designs are proposed by minimizing the IRI in the mean square error (MSE) of the least square (LS) channel estimation. The impact of frequency offset on the channel estimation accuracy is derived. The pairwise error probability (PEP) with both the frequency offset and channel estimation errors is evaluated. The power allocation is discussed. For multiple-input multiple-output (MIMO) OFDMsystems, channel and frequency offset estimation errors are investigated. The signal-to-interference-and-noise ratio (SINR) is first analyzed given channel and frequency offset estimation errors. The bit error rate (BER) is then approximated for multiple-antenna reception with maximal ratio combing (MRC) and equal gain combining (EGC). For orthogonal frequency-division multiplexing access (OFDMA) systems, the variance of the frequency offset estimation is derived as a function of SINR and signalto- noise ratio (SNR). This variance information is exploited to improve the accuracy of frequency offset estimators. A successive interference cancelation (SIC)-based frequency offset estimator is also developed. The accuracy of frequency offset estimation of the OFDMA uplink can also be improved by using the cooperative relaying. Both conventional amplify-and-forward (AF) relays and new decodeand-compensate-and forward (DcF) relays are studied. The frequency offset estimate is derived from combining different link estimates. In addition, when CSI is available, a scheme is proposed to adaptively switch between the cooperative and conventional (no relaying) transmissions to optimize the frequency offset estimation.
Doppler Spread Estimation by Subspace Tracking for OFDM Systems  [PDF]
Xiaochuan Zhao,Tao Peng,Ming Yang,Wenbo Wang
Mathematics , 2008,
Abstract: This paper proposes a novel maximum Doppler spread estimation algorithm for OFDM systems with the comb-type pilot pattern. By tracking the drifting delay subspace of the multipath channel, the time correlation function is measured at a high accuracy, which accordingly improves the estimation accuracy of the maximum Doppler spread considerably.
Study on Performance of Turbo Product Coded OFDM with LS Channel Estimation and Diversity Reception

Liu Wei,Zhang Hai-lin,Liu Zeng-ji,

电子与信息学报 , 2004,
Abstract: The low-complexity Least Square (LS) channel estimation in Orthogonal Frequency Division Multiplexing (OFDM) is studied in this paper. To reduce the error floor of OFDM with LS channel estimation, the diversity reception and turbo product coding are used in system design. The simulation results show that the turbo product coding and diversity combining can reduce the error floor in seriously frequency-selective channel. The gap of the OFDM system with LS channel estimation and with channel state information is only 4dB.
Artificial Neural Network Channel Estimation for OFDM System
Kanchan Sharma,Shweta Varshney
International Journal of Electronics and Computer Science Engineering , 2012,
Abstract: This paper uses Artificial Neural Network (ANN) for channel estimation based on Levenberg-Marquardt training algorithm in OFDM systems over Rayleigh fading channels. This technique utilizes the learning property of neural network. By using this feature, there is no need of any matrix computation and proposed technique is less complex. This technique is useful to achieving the high data rate, transmission capability with high bandwidth, efficiency and its robustness to multipath delay. In OFDM system, the Channel estimation is an essential problem so the Pilot-aided channel estimation has been used; a good choice of the pilot pattern should match the channel behavior both in time and frequency domains. In this arrangement, the performance of the channel estimation is analyzed with estimators based on Least Square Algorithm is carried out through MATLAB Simulation. The performance of OFDM with ANN is evaluated on the basis of Bit Error Rate (BER). The OFDM with ANN has been shown to perform much better than the OFDM without ANN.
Analysis of OFDM System using Pilot Channel Estimation  [PDF]
Amit,Rajesh Kumar,Priyanka Jangra
International Journal of Computer Science and Management Studies , 2012,
Abstract: Orthogonal Frequency Division Multiplexing (OFDM) ismultiplexing technology of orthogonal multicarrier, and thechannel estimation model based on pilot in OFDM systemsis analyzed; Now that, the channel estimation based onpilot needs interpolation, in order to reduce the complexityof the interpolation algorithm, the FFT channel estimationalgorithm based on pilot is studied. Because of the directFFT channel estimation algorithm existing energy spectrumleakage problems, the optimized FFT channel estimationalgorithm based on the Hamming windowed function is putforward. A lot of conventional algorithms have tried tocancel the residual frame synchronization error (RFSE),which causes the performance degradation of channelestimation when using interpolation between pilot subcarriersin comb-type pilot-aided OFDM systems.Orthogonal frequency-division multiplexing (OFDM) is atransmission technique that is based on many orthogonalcarriers that are transmitted simultaneously. Channelestimation techniques for OFDM systems, based on combtypepilot arrangement, over frequency-selective Rican andtime-varying fading channel are investigated. Theadvantage of comb-type pilot arrangement, in channelestimation, is the ability to track the variation in thechannel, which is the main reason for inter-carrierinterference modeled as an additive white Gaussian noise,leading to an increase in the noise level.
A maximum entropy approach to OFDM channel estimation  [PDF]
Romain Couillet,Merouane Debbah
Mathematics , 2008,
Abstract: In this work, a new Bayesian framework for OFDM channel estimation is proposed. Using Jaynes' maximum entropy principle to derive prior information, we successively tackle the situations when only the channel delay spread is a priori known, then when it is not known. Exploitation of the time-frequency dimensions are also considered in this framework, to derive the optimal channel estimation associated to some performance measure under any state of knowledge. Simulations corroborate the optimality claim and always prove as good or better in performance than classical estimators.
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