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EM/sage Based ML Channel Estimation for Uplink DS-CDMA Systems over Time-Varying Fading Channels

IEEE COMMUNICATIONS LETTERS 2008年第10期12卷 740-742页

作者： Dogan, Hakan Istanbul Univ Dept Elect & Elect Engn TR-34320 Istanbul Turkey

The matrix inversion for the maximum likelihood (ML) channel estimation requires high complexity for the direct-sequence code-division multiple-access (DS-CDMA) systems. The prime motivation of the paper is to propose channel estimators that achieve mean square error (MSE) performance of ML channel estimator in an iterative manner without any matrix inversion. Therefore, two computationally efficient solutions to the problem of ML channel estimation are proposed. We compare the both algorithms in terms of the number of used iteration and show that the proposed algorithms converge the same MSE performance of the ML estimator as the increasing number of iterations.

关键词： Expectation-maximization (EM) algorithm sage algorithm channel estimation DS-CDMA

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Modeling and estimation of the direction-delay power spectrum of the propagation channel

Modeling and estimation of the direction-delay power spectru...

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3rd IEEE International Symposium on Control, Communications and Signal Processing (ISCCSP 2008)

作者： Yin, Xuefeng Liu, Lingfeng Pedersen, Troels Nielsen, Daniel K. Fleury, Bernard H. Aalborg Univ Sect Nav & Commun Dept Elect Syst Aalborg Denmark

ISBN: (纸本)9781424416875

In this contribution, a multi-variate probability density function (pdf) is derived and used to describe the normalized direction-(i.e. azimuth and elevation)-delay power spectral density of individual dispersed components in the response of the propagation channel. This pdf maximizes the entropy under the constraint that its first and second moments are specified. We use a sage algorithm, as an approximation of the maximum-likelihood method, to estimate the parameters of the component direction-delay power spectral densities from measurement data. The experimental results show that the proposed pdf and the sage algorithm form altogether an effective tool to characterize direction-delay dispersion in the propagation channel.

关键词： propagation channel direction-delay power spectrum sage algorithm

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Modeling and Estimation of the Direction-Delay Power Spectrum of the Propagation Channel

Modeling and Estimation of the Direction-Delay Power Spectru...

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3rd International Symposium on Communications, Control, and Signal Processing (ISCCSP 2008), vol.1

作者： Xuefeng Yin Lingfeng Liu Troels Pedersen Daniel K. Nielsen Bernard H. Fleury Section Navigation and Communications Department of Electronic Systems University of Aalborg Aalborg Denmark Electromagnetics Microwave Communication Department of Electricity Université Catholique de Louvain Louvain-la-Neuve Belgium Forschungszentrum Telekommunikation Wien Vienna Austria

关键词： Propagation channel Direction-delay power spectrum sage algorithm

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On some near optimal low complexity detectors for MIMO fading channels

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2007年第4期6卷 1182-1186页

作者： Xie, Yongzhe Li, Qiang Georghiades, Costas N. Texas A&M Univ Dept Elect Engn College Stn TX 77843 USA

We introduce several low complexity sub-optimal MIMO detection schemes based on the List-BLAST algorithm, which exhausts the constellation points in the first layer of a BLAST scheme to generate multiple candidate solutions from which the maximum likelihood solution is determined. The candidates can also be used as initial points for the space alternating generalized expectation-maximization (sage) algorithm to further improve performance. The proposed schemes can achieve close to optimal performance for both hard and soft output detection with lower complexity than that of the sphere detection in our simulation settings.

关键词： BLAST EM algorithm sage algorithm MIMO sphere decoding detection

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Direction of arrival (DOA) parameter estimation with the sage algorithm

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SIGNAL PROCESSING 2004年第3期84卷 619-629页

作者： Verhaevert, J Van Lil, E Van de Capelle, A Katholieke Univ Leuven Div ESAT TELEMIC B-3001 Louvain Belgium

In this study, we investigate the estimation of the relative delay, the azimuth and elevation angle and the complex amplitude of a known received signal with the space alternating generalised expectation (sage) maximisation algorithm. This optimisation algorithm is used to replace the high-dimensional optimisation procedure, necessary to compute the joint maximum likelihood estimate of the parameters using several separate maximisation processes, which can be performed sequentially. Spherical arrays provide wide scan coverage with low grating lobe levels. Because a uniform antenna element distribution on this spherical surface gives rise to the smallest variations in received signal levels over the whole angular space, a uniform distribution of antennas on a sphere is used. For this completely general three-dimensional array, we have for the first time investigated the resolution of the sage algorithm, the convergence and the bit error rate as a function of the signal to noise ratio. We will show that this algorithm is a powerful tool that can be applied successfully for high-resolution parameter extraction. (C) 2003 Elsevier B.V. All rights reserved.

关键词： smart antennas DOA maximum likelihood sage algorithm

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Improved sage algorithm for PET image reconstruction using rescaled block-iterative method

Improved SAGE algorithm for PET image reconstruction using r...

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26th Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society

作者： Zhu, HQ Zhou, J Shu, HZ Li, SY Luo, LM Southeast Univ Dept Biol Sci & Med Engn Nanjing 210096 Peoples R China

ISBN: (纸本)0780384393

Iterative reconstruction methods such as the expectation maximization maximum likelihood (EMML) method can be accelerated by using a resealed block-iterative (RBI) algorithm. It was demonstrated that the space-alternating generalized expectation-maximization (sage) algorithm is superior to the EMML due to the following facts: (1) The hidden data spaces can be appropriately chosen and then be used in sage algorithm to speed up the convergence rate. (2) sage algorithm updates the parameters sequentially which makes its M-step to be treated more easily. In this paper, we present a novel algorithm that combines the RBI algorithm with sage algorithm. The convergence property of RBI-sage is discussed, and the image quality is assessed with mean absolute error and chi-square error. The experimental results show that the proposed method is more effective than the sage algorithm even if the projection data includes statistic noise.

关键词： block-iterative algorithm sage algorithm image reconstruction convergence properties

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Recursive EM and sage-inspired algorithms with application to DOA estimation

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2005年第8期53卷 2664-2677页

作者： Chung, PJ Böhme, JF Natl Chiao Tung Univ Dept Elect Engn Hsinchu 300 Taiwan Ruhr Univ Bochum Dept Elect Engn & Informat Sci D-44780 Bochum Germany

This paper is concerned with recursive estimation using augmented data. We study two recursive procedures closely linked with the well-known expectation and maximization (EM) and space alternating generalized EM (sage) algorithms. Unlike iterative methods, the recursive EM and sage-inspired algorithms give a quick update on estimates given new data. Under mild conditions, estimates generated by these procedures are strongly consistent and asymptotically normally distributed. These mathematical properties are valid for a broad class of problems. When applied to direction of arrival (DOA) estimation, the recursive EM and sage-inspired algorithms lead to a very simple and fast implementation of the maximum-likelihood (ML) method. The most complicated computation in each recursion is inversion of the augmented information matrix. Through data augmentation, this matrix is diagonal and easy to invert. More importantly, there is no search in such recursive procedures. Consequently, the computational time is much less than that associated with existing numerical methods for finding ML estimates. This feature greatly increases the potential of the ML approach in real-time processing. Numerical experiments show that both algorithms provide good results with low computational cost.

关键词： array processing DOA estimation EM algorithm recursive EM recursive estimation recursive sage sage algorithm stochastic approximation

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Double directional ultra wideband channel characterization in a line-of-sight home environment

Double directional ultra wideband channel characterization i...

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International Workshop on Ultra Wideband Systems/Conference on Ultra Wideband Systems and Technologies

作者： Haneda, K Takada, J Kobayashi, T Natl Inst Informat & Commun Technol UWB Technol Inst Yokosuka Kanagawa 2390847 Japan Tokyo Inst Technol Grad Sch Sci & Technol Int Dev Engn Tokyo 1528550 Japan Tokyo Denki Univ Tokyo 1018049 Japan

This paper introduces the concept of measuring double directional channels in ultra wideband (UWB) systems. Antenna-independent channel data were derived by doing the measurements in a wooden Japanese house. The data were useful for investigating the impact of UWB antennas and analyzing waveform distortion. Up to 100 ray paths were extracted using the sage algorithm and they were regarded as being dominant. The paths were then identified in a real environment, in which clusterization analyses were done using the directional information on both sides of the radio link. Propagating power was found to be concentrated around the specular directions of reflection and diffraction. This led to the observation that the spatio-temporal characteristics of extracted paths greatly reflected the structure and size of the environment. The power in the clusters indicated that the estimated 100 paths contained 73% of the total received power, while the rest existed as diffuse scattering, i.e., the accumulation of weaker paths. The practical limits of path extraction with sage were also discussed. Finally, we derived the scattering loss and intra-cluster properties for each reflection order, which were crucial for channel reconstrucion based on the deterministic approach.

关键词： ultra wideband UWB channel models sage algorithm spatio-temporal analysis

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Experimental determination of propagation paths for the ETC system - Equipment development and field test

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IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES 2004年第11期E87A卷 3008-3015页

作者： Haneda, K Takada, J Iwata, T Wakinaka, Y Kunishima, T Tokyo Inst Technol Dept Int Dev Engn Tokyo 1528552 Japan Japan Publ Highway Corp Tokyo 1008979 Japan Takenaka Corp Chiba 2701395 Japan

Electronic Toll Collection (ETC), an application of Dedicated Short Range Wireless Communication (DSRC), had suffered from wrong operations due to multipath problems. To solve this problem, we proposed to apply a simple configured path determination scheme for the ETC system. The system consists of a vector network analyzer, low-noise amplifier, and X-Y positioner and achieves an automatic measurement of the spatial transfer function with emphasis on accurate measurement and reproducibility. For the reliable identification of the propagating paths, 3-D Unitary ESPRIT and sage algorithms were employed. Having developed the system, field experiments at the toll gate of the highway was carried out. In the measurements, we could determine many propagation paths so that the dominant propagation phenomena at the toll gate was identified. They included a ground-canopy twice reflected wave, which was a potential path that caused wrong operation. Consequently, their reflection coefficients and polarization characteristics were investigated. From the results, applicability of the path determination system for short range on-site measurement was confirmed.

关键词： ETC DSRC propagation short range wireless communication measurement system path determination 3-D unitary ESPRIT sage algorithm

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Joint multi-dimensional channel parameter estimation schemes for DS-CDMA systems using a modified version of the sage algorithm

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IEICE TRANSACTIONS ON COMMUNICATIONS 2001年第3期E84B卷 511-519页

作者： Senhaji, YR Yamazato, T Katayama, M Ogawa, A Nagoya Univ Dept Informat Engn Grad Sch Engn Nagoya Aichi 4648603 Japan Nagoya Univ Ctr Informat Media Studies Nagoya Aichi 4648603 Japan Meijo Univ Sch Sci & Technol Dept Informat Sci Nagoya Aichi 4688502 Japan

A modified version of the sage algorithm is presented for joint delay-azimuth-attenuation parameters' estimation in a multiuser DS-CDMA system. The introduced modification consists of using different time interval lengths wizen calculating the time correlations for optimizing the different channel parameters. This modification was proposed for the purpose of a further reduction in the algorithm's computational weight in case of receiving sufficiently resolvable waves. Specifically, we found that short interval windows are sufficient for estimating delays and azimuth angles, which is quite effective in reducing the computational burden in their optimization processes. As for the estimation of the attenuation parameters, a longer time window, equal to the preamble length, is considered for more accurate estimation. Also two other estimators are proposed. The first one combining the modified sage with a sequential estimation of the attenuation parameters, suitable for slowly varying channels. Another one, similar to the first, and primarily designed to alleviate the influence of present strong interferers. Through a numerical example, the performances of the three presented estimation schemes, in terms of their near-far resistance, are compared. And it is shown that the proposed second combined estimator outperforms the modified sage in environments with high MAI levels.

关键词： channel parameter estimation EM algorithm sage algorithm Cramer-Rao lower bound maximum-likelihood estimation

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