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Model order estimation for joint demodulation in DS-CDMA systems

AEU-INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATIONS 2002年第1期56卷 27-35页

作者： Dahlhaus, D Swiss Fed Inst Technol Swiss Fed Inst Technol Commun Tech Lab CH-8092 Zurich Switzerland

An iterative algorithm for estimating the number of relevant transmission paths characterized by the model order vector L in the uplink of a direct sequence code division multiple access (DS-CDMA) system is presented. Estimates of simple lower bounds on the probability of correct one-shot symbol estimates are formulated as a function of bit-error rate estimates of all users and maximized w.r.t. L. The joint demodulation for a given value L is accomplished using a combination of a space-alternating generalized expectation-maximization (sage) algorithm for channel parameter estimation and a multistage detector. Simulation results indicate that the model order is estimated correctly even in situations with considerably different signal power levels.

关键词： multiuser detection multipath propagation bearing estimation sage algorithm near-far effect

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Exploiting a priori information for iterative channel estimation in block-fading amplify-and-forward cooperative networks

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EURASIP JOURNAL ON WIRELESS COMMUNICATIONS AND NETWORKING 2014年第1期2014卷 1页

作者： Aerts, Nico Avram, Iancu Moeneclaey, Marc UGent TELIN B-9000 Ghent Belgium

In an amplify-and-forward cooperative network, a closed-form expression of the a priori distribution of the complex-valued gain of the global relay channel is intractable, so that a priori information is often not exploited for estimating this gain. Here, we present two iterative channel gain and noise variance estimation algorithms that make use of a priori channel information and exploit the presence of not only pilot symbols but also unknown data symbols. These algorithms are approximations of maximum a posteriori estimation and linear minimum mean-square error estimation, respectively. A substantially reduced frame error rate is achieved as compared to the case where only pilot symbols are used in the estimation.

关键词： Cooperative communication MAP estimation Amplify-and-forward sage algorithm

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Two EM-Type channel estimation algorithms for OFDM with transmitter diversity

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IEEE TRANSACTIONS ON COMMUNICATIONS 2003年第1期51卷 106-115页

作者： Xie, YZ Georghiades, CN Texas A&M Univ Dept Elect Engn College Stn TX 77843 USA

We study channel estimation for orthogonal frequency-division multiplexing (OFDM) systems utilizing transmitter diversity and operating over multipath fading channels. Two expectation-maximization (EM)-type algorithms are introduced and compared with each other in terms of convergence rate. At each iteration and for every OFDM link, the EM-type algorithms partition the problem of estimating a multi-input channel into independent channel estimations for each transmit-receive antenna pair, therefore avoiding the matrix inversion encountered in the joint least-square estimation. The EM-type algorithms can also be used to efficiently implement a recently proposed algorithm, termed the significant-tap-catching estimator, so that the system performance is more robust to different multipath channel delay profiles.

关键词： expectation-maximization (EM) algorithm orthogonal frequency-division multiplexing (OFDM) sage algorithm transmitter diversity

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A component-wise EM algorithm for mixtures

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JOURNAL OF COMPUTATIONAL AND GRAPHICAL STATISTICS 2001年第4期10卷 697-712页

作者： Celeux, G Chrétien, S Forbes, F Mkhadri, A INRIA Rhone Alpes ZIRST F-38334 Saint Ismier France Univ Franche Comte Dept Math F-25030 Besancon France Univ Cadi Ayyad Marrahesh Fac Sci Semlalie Dept Math Marrakech Morocco

Maximum likelihood estimation in finite mixture distributions is typically approached as an incomplete data problem to allow application of the expectation-maximization (EM) algorithm. In its general formulation, the EM algorithm involves the notion of a complete data space, in which the observed measurements and incomplete data are embedded. An advantage is that many difficult estimation problems are facilitated when viewed in this way. One drawback is that the simultaneous update used by standard EM requires overly informative complete data spaces, which leads to slow convergence in some situations. In the incomplete data context, it has been shown that the use of less informative complete data spaces, or equivalently smaller missing data spaces, can lead to faster convergence without sacrifying simplicity. However, in the mixture case, little progress has been made in speeding up EM. In this article we propose a component-wise EM for mixtures. It uses, at each iteration, the smallest admissible missing data space by intrinsically decoupling the parameter updates. Monotonicity is maintained, although the estimated proportions may not sum to one during the course of the iteration. However, we prove that the mixing proportions will satisfy this constraint upon convergence. Our proof of convergence relies on the interpretation of our procedure as a proximal point algorithm. For performance comparison, we consider standard EM as well as two other algorithms based on missing data space reduction, namely the sage and AECME algorithms. We provide adaptations of these general procedures to the mixture case. We also consider the ECME algorithm, which is not a data augmentation scheme but still aims at accelerating EM. Our numerical experiments illustrate the advantages of the component-wise EM algorithm relative to these other methods.

关键词： EM algorithm missing data space reduction mixture estimation proximal point algorithm sage algorithm

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The EM algorithm - An old folk-song sung to a fast new tune

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JOURNAL OF THE ROYAL STATISTICAL SOCIETY SERIES B-METHODOLOGICAL 1997年第3期59卷 511-540页

作者： Meng, XL vanDyk, D HARVARD UNIV CAMBRIDGEMA 02138

Celebrating the 20th anniversary of the presentation of the paper by Dempster, Laird and Rubin which popularized the EM algorithm, we investigate, after a brief historical account, strategies that aim to make the EM algorithm converge faster while maintaining its simplicity and stability (e.g. automatic monotone convergence in likelihood). First we introduce the idea of a 'working parameter' to facilitate the search for efficient data augmentation schemes and thus fast EM implementations. Second, summarizing various recent extensions of the EM algorithm, we formulate a general alternating expectation-conditional maximization algorithm AECM that couples flexible data augmentation schemes with model reduction schemes to achieve efficient computations. We illustrate these methods using multivariate t-models with known or unknown degrees of freedom and Poisson models for image reconstruction. We show, through both empirical and theoretical evidence, the potential for a dramatic reduction in computational time with little increase in human effort. We also discuss the intrinsic connection between EM-type algorithms and the Gibbs sampler, and the possibility of using the techniques presented here to speed up the latter. The main conclusion of the pager is that, with the help of statistical considerations, it is possible to construct algorithms that are simple, stable and fast.

关键词： data augmentation expectation conditional maximization algorithm expectation conditional maximization either algorithm Gibbs sampler incomplete data Markov chain Monte Carlo method missing data model reduction multivariate t-distributions Poisson model positron emission tomography rate of convergence sage algorithm

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Maximum-Likelihood Channel Estimation in Block Fading Amplify-and-Forward Relaying Networks

Maximum-Likelihood Channel Estimation in Block Fading Amplif...

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12th IEEE International Workshop on Signal Processing Advances in Wireless Communications

作者： Aerts, Nico Avram, Iancu Moeneclaey, Marc Univ Ghent Dept Telecommun & Informat Proc B-9000 Ghent Belgium

ISBN: (纸本)9781424493326

Several diversity techniques have been proposed to counteract the effect of fading on the error performance of wireless networks. A recent and promising technique, which achieves spatial diversity without increased hardware demands, is cooperative communication, involving other terminals in the network that relay the information broadcasted by the source terminal to the destination terminal. In literature several cooperative protocols have been studied under the simplifying assumption that all channel state information is available at the destination. In this paper, we use the space-alternating generalized expectation-maximization (sage) algorithm to perform code-aided iterative channel estimation from the broadcasted signals in an Amplify-and-Forward protocol, and investigate the resulting error performance.

关键词： Cooperative Communication Amplify-and-Forward sage algorithm Maximum-Likelihood

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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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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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Basestation 3-Dimensional Spatial Propagation Characteristics in Urban Microcell at 28 GHz 11

Basestation 3-Dimensional Spatial Propagation Characteristic...

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11th European Conference on Antennas and Propagation (EUCAP)

作者： Jiang, Tao Tian, Lei Tang, Pan Hu, Zhixue Zhang, Jianhua Beijing Univ Posts & Telecommun Key Lab Universal Wireless Commun Minist Educ POB 92 Beijing 100876 Peoples R China

ISBN: (纸本)9788890701870

This paper presents a millimeter wave channel measurement in Urban Microcell (UMi) scenario at 28 GHz with a bandwidth of 400 MHz. During measuring, a steerable horn antenna is used at receiver (RX) side while an omnidirectional antenna is used at transmitter (TX) side. The horn antenna not only rotates in azimuth with a step of 5 ffi but also points into three different vertical angles. Based on the measured data, the 3-dimensional (3D) space characteristics of the millimeter wave channel are analyzed at the basestation (BS) side, e.g., azimuth angular spread of arrival (AASA), elevation angular spread of arrival (EASA) and their clustering results, by using the Space-Alternating Generalized Expectation-maximization (sage) algorithm and KPowerMeans algorithm. Through comparing the power angular profiles (PAPs) of raw data (RD) and sage results, the dynamic range of sage results will increase. The positive correlation between the measured distance and EASA is also investigated here.

关键词： channel measurement channel statistical characteristics 28 GHz horn antenna sage algorithm

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Decision Directed Channel Estimation for Improving Performance in LTE-A

Decision Directed Channel Estimation for Improving Performan...

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44th Asilomar Conference on Signals, Systems and Computers

作者： Ketonen, Johanna Juntti, Markku Ylioinas, Jari Univ Oulu Ctr Wireless Commun POB 4500 FIN-90014 Oulu Finland Nokia Siemens Networks FIN-90014 Oulu Finland

ISBN: (纸本)9781424497218

The use of decision directed (DD) channel estimation in a MIMO-OFDM downlink receiver with a LTE pilot structure is studied in this paper. The space-alternating generalized expectation-maximization (sage) algorithm is used to improve the receiver performance from the one obtained by using the pilot symbol based least-squares (LS) channel estimator. The DD channel estimation improves the performance with high user velocities, where the pilot symbol density is not sufficient. The DD channel estimation can also be used to reduce the pilot overhead without any performance degradation by transmitting data instead of pilot symbols. The complexity of the sage channel estimator is discussed as well.

关键词： channel estimation Pilots degradation of performance Mentoring sage algorithm

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