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ABSTRACT: Independent component analysis (ICA) is a widely used multivariate analysis technique with applications in many diverse fields such as medical imaging, image processing and data mining. Up to date almost all ICA research have focused on estimation of the mixing and demixing matrix but almost nothing exists on testing hypotheses of the mixing vectors or mixing coefficients. In this paper, we construct tests for this purposes using deflation-based FastICA estimator. The developed (Wald-type) test statistic utilizes the asymptotic covariance matrix of the estimator and its asymptotic normality. The developed test can be used e.g. in fMRI analysis where the mixing vectors correspond to the time courses of the independent spatial maps. In this context, it is of interest to test if the hypothesized task-related time course is significantly different from the found mixing vectors. Simulations and an example on synthetic data illustrate the validity and usefulness of our approach.
Biomedical Imaging: From Nano to Macro, 2011 IEEE International Symposium on; 05/2011
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ABSTRACT: Complex-valued signals arise in many diverse fields such as communications, radar, biomedical sciences, physical sciences, and related fields. This paper briefly reviews some important tools, statistics, models and estimators that are useful for handling complex-valued random signals. Over the past four decades, circularity (i.e. invariance of the distribution under multiplication by a unit complex number) or second-order circularity (i.e. uncorrelatedness of the random vector with its complex conjugate) has been a common implicit assumption. Hence in this paper a special emphasis is put on this circularity property, as optimal signal processing methods for circular and non-circular signals are often different and choosing the right type of processing can provide significant performance gains. Topics reviewed in this paper include different types of circularity measures and detectors of circularity, complex elliptical symmetry of random variables, Cramér-Rao lower bounds on the estimation of complex-valued parameters, optimization of a real-valued cost function with respect to complex-valued parameters using CR-calculus, and complex-valued independent component analysis.
Information Theory and Applications Workshop (ITA), 2011; 03/2011
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ABSTRACT: Complex elliptically symmetric (CES) distributions constitute a flexible and broad class of distributions for many engineering applications and include the widely used complex Gaussian, complex -, complex generalized Gaussian and symmetric -stable distributions for example. Their careful statistical characterization is needed. Moreover, the mechanisms for generating random variables from these distributions are not well defined in literature. In this paper we provide such treatment in order to provide a better insight on their statistical properties and simplifying proofs and derivations. For example, insightful expressions for complex kurtosis coefficients of CES distributions are derived providing an interpretation on what complex kurtosis really measures. Also derived are asymptotic distributions of circularity measures, the sample circularity quotient and coefficient, assuming i.i.d. samples from an unspecified CES distribution. Also new Wald's type detectors of circularity are proposed that are valid within CES distributions with finite fourth-order moments. These results are accompanied with examples that are of interest in developing signal processing algorithms for complex-valued signals.
IEEE Transactions on Signal Processing 02/2011; · 2.63 Impact Factor
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ABSTRACT: Complex random signals play an increasingly important role in array, communications, and biomedical signal processing and related fields. However, the fundamental properties of complex-valued signals and mathematical tools needed to process them are scattered in literature. We provide a concise, unified, and rigorous treatment of essential properties and tools of complex random variables, and apply these fundamentals to derive complex extensions of Leibniz rule, Faá di Bruno's formula, and Taylor's series. The extensions allow establishing relationships among complex moments and cumulants, and characterizing the circularity property. We propose measures for testing and quantifying circularity, and observe that non-circularity may be more common in practical applications than previously thought. All results are rigorously proved and supplemented with clarifying examples.
IEEE Transactions on Signal Processing 11/2010; · 2.63 Impact Factor
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ABSTRACT: Recent research have elucidated that significant performance gains can be achieved by exploiting the circularity/non-circularity property of the complex-valued signals. The generalized likelihood ratio test (GLRT) of circularity assuming complex normal (Gaussian) sample has an asymptotic chi-squared distribution under the null hypothesis, but suffers from its sensitivity to Gaussianity assumption. With a slight adjustment, by diving the test statistic with an estimated scaled standardized 4th-order moment, the GLRT can be made asymptotically robust with respect to departures from Gaussianity within the wide-class of complex elliptically symmetric (CES) distributions while adhering to the same asymptotic chi-squared distribution. Our simulations demonstrate the validity of the chi<sup>2</sup> approximation even at small sample lengths. A practical communications example is provided to illustrate its applicability. In passing, we derive the connection with the kurtosis of a complex random variable with a CES distribution with the kurtosis of its real and imaginary part.
Signal Processing Advances in Wireless Communications, 2009. SPAWC '09. IEEE 10th Workshop on; 07/2009
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ABSTRACT: In this paper, we consider array processors that are scale-invariant functions of the array covariance matrix. The emphasis is on Capon's MVDR beamformer. We call such an array processor as scatter matrix based (SMB) array processor since the covariance matrix is required only up to a constant scalar and thus a scatter matrix (proportional to covariance under finite covariance assumption) provides sufficient information. In order to establish interesting statistical robustness and large sample properties, we derive a general expression for the influence function and the asymptotic covariance structure of SMB-MVDR beamformer weights. Our results apply under the class of complex elliptically symmetric distributions, which includes the commonly used complex normal distribution as a special case. We illustrate the theory by deriving the IF and asymptotic relative efficiencies of the conventional SMB-MVDR beamformer that employs the sample covariance matrix and beamformers that employ robust M -estimators of scatter. Theoretical findings are confirmed by simulations. Our findings favor beamformers based upon M -estimators of scatter, since they combine a high efficiency with appealing robustness properties.
IEEE Transactions on Signal Processing 02/2009; · 2.63 Impact Factor
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ABSTRACT: Despite of the increased interest in independent component analysis (ICA) during the past two decades, a simple closed form expression of the Cramer-Rao bound (CRB) for the demixing matrix estimation has not been established in the open literature. In the present paper we fill this gap by deriving a simple closed-form expression for the CRB of the demixing matrix directly from its definition. A simulation study comparing ICA estimators with the CRB is given.
IEEE Transactions on Signal Processing 05/2008; · 2.63 Impact Factor
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ABSTRACT: In this paper, we derive a stochastic maximum-likelihood (ML) method for estimating spatio-temporal parameters for multiple-input multiple-output (MIMO) channels. Such estimators are needed in propagation studies where extensive channel measurements and sounding are required. These are seminal tasks in the process of developing advanced channel models. The proposed method employs an angular von Mises distribution model which is appropriate for angular data observed in channel measurement campaigns. The signal model is stochastic, and consequentially the method is particularly useful for estimation of the diffuse scattering component. This approach leads to lower complexity and faster convergence in comparison to deterministic models. These benefits are due to lower dimensionality of the model, leading to a simpler optimization problem. The statistical performance of the estimator is studied by establishing the Crameacuter-Rao lower bound (CRLB) and comparing the variances. The simulations show that the variance of the proposed estimation technique reaches the CRLB for relatively small sample size. The estimator is robust in the sense that meaningful results are obtained when applied to data generated by channel models other than the one used in its derivation
IEEE Transactions on Signal Processing 02/2007; · 2.63 Impact Factor
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ABSTRACT: For the development of future wireless systems, it is crucial to create accurate channel models. Channel sounding using antenna arrays and consequently propagation parameter estimation are key tasks in creating such models. In this paper we present an estimator for the angular distribution of the diffuse scattering component that is observed in channel sounding measurements. The angular distribution is modeled as a mixture of Von Mises distributions, which correspond to scatterer clusters. The parameters of the individual distributions as well as the mixture proportions are estimated. The large sample performance of the estimator is studied by deriving the Cramer-Rao lower bound and comparing the variance of the estimates to it. The simulations show that the the proposed estimator has asymptotically optimal performance since it attains the Cramer-Rao lower bound for relatively small sample sizes.
Acoustics, Speech, and Signal Processing, 2005. Proceedings. (ICASSP '05). IEEE International Conference on; 04/2005 · 4.63 Impact Factor
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ABSTRACT: Realistic channel models are crucial in developing future wireless systems. Channel sounding and consequently propagation parameter estimation are key tasks in creating such models. In this paper we present an estimator for the angular distribution of the diffuse scattering component that is frequently observed in channel sounding measurements. Finding the Cramer-Rao lower bound and comparing the variances study the large sample performance of the estimator. The simulations show that the variance of the proposed estimation technique closely reaches the Cramer-Rao lower bound for small sample size and for any number of antennas.
Signals, Systems and Computers, 2004. Conference Record of the Thirty-Eighth Asilomar Conference on; 12/2004
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ABSTRACT: We will derive a stochastic maximum likelihood method for estimating spatio-temporal channel parameters. Such estimators are needed in propagation studies where extensive channel measurements and sounding are required. These are seminal tasks in the process of developing advanced channel models. The proposed method employs angular Von Mises distribution model which is appropriate for directional data typically observed in channel measurement campaigns. The signal model is stochastic. The performance of the proposed method is compared to SAGE algorithm where the signal model is deterministic. The computational complexity of the proposed method is lower and channel parameters are estimated with higher fidelity because the underlying distribution model is well-suited for directional data.
Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
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ABSTRACT: We introduce a new class of distributions called generalized complex elliptically symmetric distributions. Several distributions commonly used in the literature, for example, the multivariate complex normal and Cauchy and the generalized complex normal distribution, are prominent members of this class. The treatment covers both proper and improper random vectors and goes beyond second-order concepts in defining the distribution model. Some properties of these distributions are studied and illustrative examples of their applications in multichannel signal processing are presented such as tests for circularity.
Sensor Array and Multichannel Signal Processing Workshop Proceedings, 2004; 08/2004
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ABSTRACT: In this paper we propose a robust method for estimation of the space-time array scatter matrix, i.e. the space-time pseudo-covariance matrix of the antenna array observations. Such scatter matrix and the subspaces spanned by its eigenvectors serve as a basis of broadband beamforming, high-resolution angle of arrival estimation methods and maximum likelihood array processing algorithms. The proposed estimator is based on a heavy-tailed probability model. Robustness and computational issues of the estimator are discussed. The considered estimator can be calculated using a simple iterative algorithm where no user-defined tuning constants are needed. The robust performance of the estimator is demonstrated in MVDR beamforming and GPS receiver examples, using a space-time uniform linear array (ULA). We demonstrate that the method is highly robust and suffers only a small performance loss in additive white Gaussian noise conditions.
Vehicular Technology Conference, 2003. VTC 2003-Fall. 2003 IEEE 58th; 11/2003
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ABSTRACT: This paper addresses the problem of antenna array processing in nonGaussian noise and interference conditions. Such conditions arise due to man-made interference in indoor and outdoor mobile communication channels as well as in military communications. In this paper M-estimators of the array (pseudo-)covariance matrix based upon complex data set are introduced. Estimates of the noise and signal subspaces based on M-estimators are then used to robustify the subspace direction of arrival (DOA) estimation methods. In addition, eigenvalues based on M-estimators are used in MDL criterion, thus yielding a robust signal detection method. The reliable performance of the proposed methods are shown by simulations.
Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003. 14th IEEE Proceedings on; 10/2003
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ABSTRACT: The international population policy agenda has traditionally been dominated by demographically driven population control policies. However, in the population policy development that preceded the International Conference on Population and Development in 1994, people's reproductive needs and rights received more emphasis. The aim of this study was to analyze how the new emphasis in population policies has been interpreted at the country level. In analyzing population policy rhetoric and its practical interpretations in India in 1994, the authors found that the rhetoric was broadening to encompass women's empowerment and reproductive health and that the use of direct method-specific monetary incentives and disincentives for accepting family planning methods was disapproved. However, population policy options were still considered mainly in terms of their ability to reduce fertility. Furthermore, the increased emphasis on the general market agenda was more important than that on reproductive needs and rights in molding population policies, as was evident in the greater stress on cost-recovery systems and nongovernmental actors. The findings suggest that the broader agenda for population policies and reproductive rights has been interpreted so that it can serve the aims of population-growth control and be implemented in the context of more market-oriented social policies and trade liberalization.
International Journal of Health Services 02/2000; 30(1):87-110. · 1.21 Impact Factor
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ABSTRACT: Norplant and Norplant-2 have been available for use by Finnish women since 1984 and 1986, respectively. The objective of this study was to explore Norplant users' experiences of insertions, removals and medical treatments.
A questionnaire was sent to women who had received Norplant or Norplant-2 implants one to two years earlier (n = 262) in normal clinical settings; the response rate was 79%.
At insertion, problems were experienced by 9% and at least some pain by 23% of women. During the first year 20% of all users (14% of Norplant and 33% of Norplant-2 users) had their implants removed. Problems were experienced at removal by 33% of women and pain was experienced by 40%; nevertheless most users were satisfied with the device. Findings were similar for the two types of Norplant. Forty-two percent of the women had received minipills containing levonorgestrel before Norplant insertions in an attempt to assess Norplant's suitability, and 8% had received drugs for adverse effects caused by Norplant.
Studies including perspectives of Norplant users and the whole lifespan of Norplant (including removal) should be conducted in all clinical settings where Norplant is provided.
British Journal of Obstetrics and Gynaecology 05/1997; 104(4):488-94.
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ABSTRACT: Objective Norplant® and Norplant-2® have been available for use by Finnish women since 1984 and 1986, respectively. The objective of this study was to explore Norplant users’ experiences of insertions, removals and medical treatments.Design A questionnaire was sent to women who had received Norplant® or Norplant-2® implants one to two years earlier (n= 262) in normal clinical settings; the response rate was 79%.Results At insertion, problems were experienced by 9% and at least some pain by 23% of women. During the first year 20% of all users (14% of Norplant® and 33% of Norplant-2® users) had their implants removed. Problems were experienced at removal by 33% of women and pain was experienced by 40%; nevertheless most users were satisfied with the device. Findings were similar for the two types of Norplant. Forty-two percent of the women had received minipills containing levonorgestrel before Norplant insertions in an attempt to assess Norplant's suitability, and 8% had received drugs for adverse effects caused by Norplant.Conclusions Studies including perspectives of Norplant users and the whole lifespan of Norplant (including removal) should be conducted in all clinical settings where Norplant is provided.
BJOG An International Journal of Obstetrics & Gynaecology 03/1997; 104(4):488 - 494. · 3.41 Impact Factor
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ABSTRACT: Norplant implantable contraceptives were developed mainly for use in Third World countries, but first were approved for marketing in Finland in 1983 and in Sweden in 1985. Since then Norplant has been approved in more than 40 countries, most of them in the Third World. The authors analyzed the clinical documentation submitted to the Finnish and Swedish drug control authorities, and the assessments made of the data. The Finnish review process lasted for three years, and the number of data increased substantially during that time. The authors have not been allowed to publish the clinical data submitted in Finland, but a reconstruction from the Swedish data showed that the clinical data were of poor quality and were mainly focused on assessing efficacy. Side effects, acceptability, and requirements of the health care system for proper use of Norplant were poorly studied. This example of Norplant licensing in Finland shows that licensing of drugs in industrialized countries is insufficient for guaranteeing their safety in Third World countries.
International Journal of Health Services 02/1997; 27(2):309-28. · 1.21 Impact Factor
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ABSTRACT: The objective of this paper is to describe secrecy in drug regulation in Finland, by recording and reporting our experience in obtaining Norplant® licensing documentation. The materials used are the documents, phone calls and other contacts recorded in a research diary that were produced while relevant authorities considered our application to obtain the documents and the publication of our manuscript. The application process was complicated, and it took three years to obtain the licensing documentation and two years to try, unsuccessfully, to get permission to publish the manuscript. In the course of these procedures we made 188 active contacts, and the authorities wrote several memoranda. The drug regulatory authority and the manufacturer wanted to categorise the whole licensing process as a trade secret, and to have the manufacturer define what a trade secret is and when trade secrets could be released, while the Ministry for Social Affairs and Health valued more open regulation. The process is still not complete because the manufacturer has sued the ministry in court about their decision to grant dispensation. It can be concluded that to enable independent research on drugs and drug regulation, the publicity status of documents must be clear, and trade secrecy must be defined narrowly. Decisions on dispensation to give access to classified documents should consider the interests of public health and should be made by authorities other than the drug regulatory authority.
The International journal of risk & safety in medicine 01/1996; 9(3):161-72.
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ABSTRACT: This study was designed to assess users' perceptions of and satisfaction with the Norplant contraceptive implant.
A questionnaire was mailed to all women having had Norplant inserted one or two years before the study initiation in seven public out-patient family-planning clinics in the capital area of Finland, of whom 82% responded (n = 207).
Practically all women (97%) had experienced some side-effects and 72% considered at least one of them to be disruptive. Of these side-effects, bleeding irregularities proved most often bothersome during the first 6 months of use, but depression and nervousness were relatively more important reasons for early removal. Regardless of the ubiquity of side-effects, 78% were satisfied with Norplant. High satisfaction was common especially among older users with their second set of capsules. Dissatisfaction with the method was best explained by the experience of unexpected and disruptive side-effects.
Our results suggest that mental problems related to Norplant use have received too little attention and that satisfaction is highest in carefully selected users among older women.
Acta Obstetricia Et Gynecologica Scandinavica 08/1995; 74(6):441-5. · 1.77 Impact Factor
