The Experts below are selected from a list of 5733 Experts worldwide ranked by ideXlab platform
N C Beaulieu - One of the best experts on this subject based on the ideXlab platform.
-
robust Doppler Spread estimation in nonisotropic fading channels
2005Co-Authors: Kareem E Baddour, N C BeaulieuAbstract:A new parametric approach is proposed for the estimation of the maximum Doppler frequency, or equivalently the mobile speed, in narrowband mobile radio channels. In this work, simple and efficient Doppler-frequency estimators are formulated based on using a small number of samples of the channel autocorrelation function. Unlike previous approaches, the chosen parameterization is shown to be robust in a microcellular propagation environment, which may be characterized by nonisotropic scattering and/or a specular component of unknown strength. Simulation results are described to illustrate the effects of additive noise and the finite data-record performance.
-
nonparametric Doppler Spread estimation for flat fading channels
2003Co-Authors: Kareem E Baddour, N C BeaulieuAbstract:Accurate estimation of the Doppler Spread of a mobile radio channel is of significant value as it reveals the channel's rate of change. This information can then be used to improve the performance of many wireless communication subsystems. In this paper, a nonparametric technique is proposed to estimate the maximum Doppler frequency of narrow band fading channels. Moreover, a computationally efficient periodogram-based approach is formulated, and its finite sample performance is assessed and compared to parametric covariance-based estimators via computer simulations. On the basis of these comparisons, we claim that the simplicity of the proposed method, its accurate performance for small sample sizes in a wide range of propagation scenarios, and its robustness to low SNR conditions make it a strong competitor to the parametric approaches.
Heiichi Yamamoto - One of the best experts on this subject based on the ideXlab platform.
-
study for various array antenna assisted Doppler Spread compensator with mrc diversity of isdb t receiver
2005Co-Authors: Minoru Okada, Heiichi YamamotoAbstract:Digital television terrestrial broadcasting (DTTB) based on OFDM (Orthogonal Frequency Division Multiplexing) is sensitive to Doppler Spread and multi-path propagation in mobile environment. A part of authors has already proposed a Doppler Spread compensator based on linear array antenna. However, the proposed linear array antenna assisted Doppler Spread compensator did not take into account an effect of electromagnetic coupling amongst elements. Also, it did not have diversity function while it has a several elements. This paper proposes two types of array antenna assisted Doppler Spread compensators, which employ dipole array and monopole array, and which work as a maximum ratio combining (MRC) diversity as well as the Doppler Spread compensator. Computer simulation results confirm that the dipole-array receiver outperforms the monopole-array receiver.
-
array antenna assisted Doppler Spread compensator for ofdm
2002Co-Authors: Minoru Okada, Hideaki Takayanagi, Heiichi YamamotoAbstract:This paper proposes a novel Doppler Spread compensation scheme using a linear array antenna, which is parallel to the direction of movement of the vehicle. In order to mitigate performance degradation due to Doppler Spread, the compensation scheme estimates the received signal at a point that is ‘fixed’ against the ground during the observation period. Computer simulation results show the proposed compensation scheme can effectively compensate for bit error rate degradation due to Doppler Spread.
Yuh-ren Tsai - One of the best experts on this subject based on the ideXlab platform.
-
Low-complexity ML Doppler Spread estimation for OFDM systems
2014Co-Authors: Yuh-ren TsaiAbstract:[[abstract]]The time domain maximum likelihood (ML) Doppler Spread estimation for OFDM systems provides an accurate estimation performance; however, it results in a much higher computation cost. We propose a low-complexity ML Doppler estimator based on a well-designed preamble sequence along with a suboptimal ML (SML) method to reduce the computational complexity of the optimal ML scheme. Because of the proposed preamble sequence, the received samples are able to be partitioned into uncorrelated subsets, yielding a substantial complexity reduction for the SML scheme. The simulation results show that the proposed estimator provides accurate and efficient Doppler Spread estimation.[[fileno]]2030102030159[[department]]電機工程學
-
joint channel and Doppler Spread estimation over time varying flat fading channels
2012Co-Authors: Kaijie Yang, Chinliang Wang, Yuh-ren TsaiAbstract:In time-varying flat-fading environments, time domain channel correlations are required for accurate channel estimation and interpolation. However, the correlation property, which depends on the Doppler Spread, is hard to be extracted from corrupted channel responses within a short channel estimation interval. In this work, based on an approximate channel model via the Taylor expansion, we propose a joint channel and Doppler Spread estimation scheme over time-varying flat-fading channels. It employs the expectation-maximization (EM) algorithm to iteratively attain the maximum-likelihood (ML) channel and Doppler Spread estimates. Simulation results show that the proposed scheme achieves accurate performance of both channel estimation and Doppler Spread estimation within a short estimation interval.
-
approximate ml Doppler Spread estimation over flat rayleigh fading channels
2009Co-Authors: Yuh-ren Tsai, Kaijie YangAbstract:The maximum likelihood (ML) Doppler Spread estimator provides an accurate estimation performance; however, it results in a much higher computation cost. In this work, we propose a time-domain approximate-ML estimator that significantly reduces the computational complexity of the ML estimator over a flat Rayleigh fading channel. Simulation results show that the proposed method nearly achieves the exact ML performance. Moreover, by using a small number of observation samples, our proposed method gives almost unbiased Doppler Spread estimation for low to medium user mobility.
Sofiene Affes - One of the best experts on this subject based on the ideXlab platform.
-
FPGA-SDR Integration and Experimental Validation of a Joint DA ML SNR and Doppler Spread Estimator for 5G Cognitive Transceivers
2019Co-Authors: Haithem Haggui, Sofiene Affes, Faouzi BelliliAbstract:In a multi-connected, multi-technology, and pervasive mobile infrastructure, such as what is being planned for 5G, artificial intelligence and cognition will play a major role. An important goal of future mobile infrastructures is to self-adapt their characteristics to their operating conditions, at the physical link, as well as at the network and application layers, which gives rise to a new paradigm known as context-aware cognitive radio (CR). CR transceivers (CTRs) mostly incorporate a cognitive engine that relies on various sensorial entities, which attempt to provide sufficient information about the quality of the link through the estimation of various key channel parameters. Two important parameters are required in a wide range of CTR architectures: the signal-to-noise ratio (SNR) and the Doppler Spread. Within this context, we tackle the hardware design and integration of a joint data-aided (DA) maximum likelihood (ML) SNR and Doppler Spread estimator recently shown to outperform main state-of-the-art solutions both in terms of accuracy and complexity. We propose a deep-pipelined and resource-efficient architecture for the outlined joint DA ML estimator, and we integrate our design on an FPGA-based software-defined radio (SDR) platform. We finally validate and test this prototype in real time under realistic over-the-air propagation conditions reproduced by a highly-scalabile channel emulator. Compared to its MATLAB floating-point version, our hardware prototype suggests negligible losses in performance despite the existence of several hardware impairments, thereby confirming its very strong potential and attractiveness for possible integration in future 5G CTRs.
-
a low cost and robust maximum likelihood joint estimator for the Doppler Spread and cfo parameters over flat fading rayleigh channels
2017Co-Authors: Faouzi Bellili, Sofiene Affes, Yassine Selmi, Ali GhrayebAbstract:This paper addresses the problem of Doppler Spread and carrier frequency offset (CFO) estimation under flat-fading Rayleigh channels. We develop a new low-cost and robust approximate maximum likelihood (ML) estimator for these two key parameters that builds upon an elegant two-ray approximation model of the channel’s covariance matrix. The latter is then inverted analytically thereby yielding a closed-form expression for the underlying log-likelihood function that is prone to easy evaluation by the fast Fourier transform. Computer simulations show that the new estimator is accurate over wide ranges of the Doppler Spread and CFO parameters. Moreover, it outperforms many state-of-the-art techniques under the adverse conditions of short data records and/or low SNR thresholds. Most prominently, it exhibits an unprecedented robustness to the Doppler spectrum shape of the channel since it does not require its a priori knowledge.
-
A low-cost and robust maximum likelihood Doppler Spread estimator
2013Co-Authors: Faouzi Bellili, Sofiene AffesAbstract:This paper addresses the problem of Doppler Spread estimation in Rayleigh flat fading channels using a new low-cost and robust maximum likelihood (ML) technique. Relying on a an elegant approximation of the channel covariance matrix by a two-ray model, we are able to invert the overall approximate covariance matrix analytically thereby obtaining a low-cost closed-form approximation of the likelihood function. We show by computer simulations that the new estimator is accurate over a wide Doppler Spread range and that it outperforms many state-of-the-art techniques. In contrast to the latter, it exhibits an unprecedented robustness to the Doppler spectrum shape of the channel since it does not require its a priori knowledge.
-
robust Doppler Spread estimation in the presence of a residual carrier frequency offset
2009Co-Authors: Mehrez Souden, Sofiene Affes, Jacob Benesty, R BahrounAbstract:In high data-rate transmission systems, accurate Doppler Spread estimation is a critical task for not only mobile velocity estimation, but also for optimal adaptive processing. It is known that the residual carrier frequency offset (CFO) which is inherent to the asynchrony between the communicating ends in a wireless link has a detrimental effect on the Doppler Spread estimation. In this correspondence, we propose a new simple and accurate approach that copes with this issue by explicitly taking the CFO into account when estimating the Doppler Spread. This new approach stems from the fact that the cross-correlation of the channel is a weighted summation of monochromatic plane waves (or an inverse Fourier transform of its power spectral density). It turns out that these plane waves are locally (as compared to the sampling rate) distributed around a main frequency which is nothing but the CFO. Using this property, we base our analysis on Taylor series expansions in addition to an observation temporal aperture to develop a two-ray spectrum approximate model for the Doppler Spread estimation. We find that the Doppler Spread is half of the frequency spacing between both rays which are located symmetrically around the CFO. Finally, we deduce new closed-form estimators for the Doppler Spread and also for the CFO. These estimators are accurate and practical in environments with isotropic scattering where the channel power spectrum density (PSD) is symmetric. Simulations are provided to illustrate the advantages of the proposed method and its robustness to the CFO.
Shengli Zhou - One of the best experts on this subject based on the ideXlab platform.
-
characterization and receiver design for underwater acoustic channels with large Doppler Spread
2015Co-Authors: Yi Huang, Zhaohui Wang, Shengli ZhouAbstract:A time-varying underwater acoustic channel consists of multiple propagation paths which could have drastically distinct Doppler scaling factors. For example, in a communication scenario with mobile nodes, some paths might experience positive Doppler scales while others have negative Doppler scales, leading to a large Doppler Spread. In this work, we address two issues. First, we quantify the channel Doppler Spread of an underwater acoustic channel based on the instantaneous channel estimate from a probing signal. Second, we develop an OFDM receiver specifically for channels with large Doppler Spread. Data sets collected from a swimming pool with a moving node are used for channel characterization and performance evaluation.
-
frequency domain oversampling for zero padded ofdm in underwater acoustic communications
2012Co-Authors: Zhaohui Wang, Georgios B Giannakis, Christian R Berger, Shengli Zhou, Jie HuangAbstract:Although time-domain oversampling of the received baseband signal is common for single-carrier transmissions, the counterpart of frequency-domain oversampling is rarely used for multicarrier transmissions. This is because frequency-domain oversampling cannot be taken advantage of, when using the commonly used low-complexity receiver that assumes orthogonal subcarriers. In this paper, we explore frequency-domain over-sampling to improve the system performance of zero-padded (ZP) orthogonal frequency division multiplexing (OFDM) transmissions over underwater acoustic channels with large Doppler Spread. In these channels, intercarrier interference (ICI) has to be addressed explicitly via frequency-domain equalization, which enables inclusion of additional frequency samples at little increased complexity. We use a signal design that enables separate sparse channel estimation and data detection, reducing equalization complexity. Based on both simulation and experimental results, we observe that the receiver with frequency-domain oversampling outperforms the conventional one considerably, where the gain increases as the Doppler Spread increases.
-
frequency domain oversampling for zero padded ofdm in underwater acoustic communications
2010Co-Authors: Zhaohui Wang, Georgios B Giannakis, Christian R Berger, Shengli Zhou, Jie HuangAbstract:Although time-domain oversampling of the received baseband signal is common for single-carrier transmissions, the counterpart of frequency-domain oversampling is rarely used for multicarrier transmissions. In this paper, we explore frequency-domain oversampling to improve the system performance of zero-padded OFDM transmissions over underwater acoustic channels with large Doppler Spread. We use a signal design that enables separate sparse channel estimation and data detection, rendering a low complexity receiver. Based on both simulation and experimental results, we observe that the receiver with frequency-domain oversampling outperforms the conventional one considerably in channels with moderate and large Doppler Spreads, and the gain increases as the Doppler Spread increases. Although a raised-cosine pulse-shaping window can be used to improve the system performance relative to a rectangular window at the expense of data rate reduction, the performance gain is much less than that brought by frequency-domain oversampling in the considered OFDM system for Doppler Spread channels.
-
sparse channel estimation for multicarrier underwater acoustic communication from subspace methods to compressed sensing
2010Co-Authors: Christian R Berger, Shengli Zhou, James C Preisig, Peter WillettAbstract:In this paper, we investigate various channel estimators that exploit channel sparsity in the time and/or Doppler domain for a multicarrier underwater acoustic system. We use a path-based channel model, where the channel is described by a limited number of paths, each characterized by a delay, Doppler scale, and attenuation factor, and derive the exact inter-carrier-interference (ICI) pattern. For channels that have limited Doppler Spread we show that subspace algorithms from the array processing literature, namely Root-MUSIC and ESPRIT, can be applied for channel estimation. For channels with Doppler Spread, we adopt a compressed sensing approach, in form of Orthogonal Matching Pursuit (OMP) and Basis Pursuit (BP) algorithms, and utilize overcomplete dictionaries with an increased path delay resolution. Numerical simulation and experimental data of an OFDM block-by-block receiver are used to evaluate the proposed algorithms in comparison to the conventional least-squares (LS) channel estimator. We observe that subspace methods can tolerate small to moderate Doppler effects, and outperform the LS approach when the channel is indeed sparse. On the other hand, compressed sensing algorithms uniformly outperform the LS and subspace methods. Coupled with a channel equalizer mitigating ICI, the compressed sensing algorithms can effectively handle channels with significant Doppler Spread.
-
receiver comparisons on an ofdm design for Doppler Spread channels
2009Co-Authors: Sean Mason, Shengli Zhou, Christian Berger, Keenan Ball, Lee Freitag, Peter WillettAbstract:Underwater acoustic channels induce large Doppler drifts that render intercarrier interference (ICI) for OFDM transmissions. Assuming that after proper Doppler compensation the residual ICI is limited to only direct neighbors, we propose an OFDM signal design that decouples channel estimation and data demodulation. We investigate eight receivers that are categorized into three groups: (i) three receivers that ignore the residual ICI, (ii) three receivers that are based on a basis expansion model (BEM) and pursue channel estimation independently along each basis, and (iii) two receivers that are based on discrete-path modeling. The receiver performance is compared based on data from the SPACE experiment conducted off the coast of Martha's Vineyard, Massachusetts, October 2008. The receiver based on the discrete-path modeling and a basis pursuit algorithm achieves the best performance while the receiver based on BEM and least-squares channel estimation performs the worst. The performance differences among different receivers drastically increase as the channel's Doppler Spread and the signal constellation size increase. Interestingly, the BEM based receivers are often inferior to the ICI-ignorant counterparts, implying that the ability of ICI compensation could be limited by the estimation accuracy of the much increased number of model parameters.