异步CDMA系统中的盲多用户检测算法

针对实际应用中的DS/CDMA系统多为多径衰落信道下的异步DS/CDMA系统情况,通过对用于AWGN信道下的同步DS/CDMA系统中的常规盲多用户检测算法的改进,使这类算法在多径衰落信道下的异步DS/CDMA系统中仍具有很好的性能。理论分析和计算机仿真结果证实了改进方法的可行性。     

时分多址与码分多址数字通信系统比较分析

回顾了移动通信发展历程，介绍了移动通信领域比较流行的时分多址与码分多址蜂窝数字系统，并对时分多址与码分多址蜂窝数字通信系统进行了比较与分析，提出了21世纪移动通信的发展方向。     

Testing for equivalence of variances using Hartley's ratio

Hartley's test for homogeneity of k normal‐distribution variances is based on the ratio between the maximum sample variance and the minimum sample variance. In this paper, the author uses the same statistic to test for equivalence of k variances. Equivalence is defined in terms of the ratio between the maximum and minimum population variances, and one concludes equivalence when Hartley's ratio is small. Exact critical values for this test are obtained by using an integral expression for the power function and some theoretical results about the power function. These exact critical values are available both when sample sizes are equal and when sample sizes are unequal. One related result in the paper is that Hartley's test for homogeneity of variances is no longer unbiased when the sample sizes are unequal. The Canadian Journal of Statistics 38: 647–664; 2010 © 2010 Statistical Society of Canada     

Nonparametric likelihood and doubly robust estimating equations for marginal and nested structural models

This article considers Robins's marginal and nested structural models in the cross‐sectional setting and develops likelihood and regression estimators. First, a nonparametric likelihood method is proposed by retaining a finite subset of all inherent and modelling constraints on the joint distributions of potential outcomes and covariates under a correctly specified propensity score model. A profile likelihood is derived by maximizing the nonparametric likelihood over these joint distributions subject to the retained constraints. The maximum likelihood estimator is intrinsically efficient based on the retained constraints and weakly locally efficient. Second, two regression estimators, named hat and tilde, are derived as first‐order approximations to the likelihood estimator under the propensity score model. The tilde regression estimator is intrinsically and weakly locally efficient and doubly robust. The methods are illustrated by data analysis for an observational study on right heart catheterization. The Canadian Journal of Statistics 38: 609–632; 2010 © 2010 Statistical Society of Canada     

Model‐based linear clustering

The authors propose a profile likelihood approach to linear clustering which explores potential linear clusters in a data set. For each linear cluster, an errors‐in‐variables model is assumed. The optimization of the derived profile likelihood can be achieved by an EM algorithm. Its asymptotic properties and its relationships with several existing clustering methods are discussed. Methods to determine the number of components in a data set are adapted to this linear clustering setting. Several simulated and real data sets are analyzed for comparison and illustration purposes. The Canadian Journal of Statistics 38: 716–737; 2010 © 2010 Statistical Society of Canada     

OBM Today and Tomorrow

Abstract

In this article I present the speech I gave when accepting the OBM Network's award for outstanding achievement. In that speech I characterized the field as I understood it in 1992 and directions I thought it should take in the future, including the role that JOBM should play in that future. The acceptance speech is followed by my extensive commentary and opinion concerning developments in the field of OBM up to the year 2000 and the paths along which I think it should develop and paths I think it should avoid in the future.     

Model‐based clustering of longitudinal data

A new family of mixture models for the model‐based clustering of longitudinal data is introduced. The covariance structures of eight members of this new family of models are given and the associated maximum likelihood estimates for the parameters are derived via expectation–maximization (EM) algorithms. The Bayesian information criterion is used for model selection and a convergence criterion based on the Aitken acceleration is used to determine the convergence of these EM algorithms. This new family of models is applied to yeast sporulation time course data, where the models give good clustering performance. Further constraints are then imposed on the decomposition to allow a deeper investigation of the correlation structure of the yeast data. These constraints greatly extend this new family of models, with the addition of many parsimonious models. The Canadian Journal of Statistics 38:153–168; 2010 © 2010 Statistical Society of Canada     

Small area estimation of poverty indicators

The authors propose to estimate nonlinear small area population parameters by using the empirical Bayes (best) method, based on a nested error model. They focus on poverty indicators as particular nonlinear parameters of interest, but the proposed methodology is applicable to general nonlinear parameters. They use a parametric bootstrap method to estimate the mean squared error of the empirical best estimators. They also study small sample properties of these estimators by model‐based and design‐based simulation studies. Results show large reductions in mean squared error relative to direct area‐specific estimators and other estimators obtained by “simulated” censuses. The authors also apply the proposed method to estimate poverty incidences and poverty gaps in Spanish provinces by gender with mean squared errors estimated by the mentioned parametric bootstrap method. For the Spanish data, results show a significant reduction in coefficient of variation of the proposed empirical best estimators over direct estimators for practically all domains. The Canadian Journal of Statistics 38: 369–385; 2010 © 2010 Statistical Society of Canada     

Social Security in Italy

The United States is confronting two simultaneous demographic shifts with profound implications for public policy: population aging and increasing diversity. These changes are accelerating during a dramatic economic downturn, placing entitlement reform prominently on the national policy agenda. Using decennial census data from 2000, this paper examines the nexus of these trends by examining characteristics of Latino baby boomers. In the census data, Latinos constituted 10% of the 80 million boomers; roughly one-third of Latino boomers (37%) were born in the United States or abroad to a U.S. parent; 6% were born in a U.S. territory; 21% were naturalized citizens; and 36% were noncitizens. Compared to non-Latinos, Latino baby boomers had lower levels of education, home ownership, and investment income and higher rates of material hardship and poverty; however, there was considerable variation based on citizenship status. A better understanding of Latino baby boomers will help policy makers anticipate the retirement needs of baby boomers as the United States prepares for the aging of a racially and ethnically diverse population.     

‘The World Will Never Be the Same Again’? Reflecting on the Experiences of Jubilee 2000, Mobilizing Globally for the Remission of Unpayable Debts

The emergence of global citizen action has been widely recognized as having become part of the discourse and practice of democratic politics and social change. Jubilee 2000 was a remarkable example of global citizen action, campaigning against unpayable Third World debt. Whilst Jubilee 2000 had novel features, however, the conclusion that ‘the world will never be the same again’ invites further exploration, both in relation to the implications for theoretical debates and in relation to social movements as these have been developing globally, in practice.

This paper starts by summarizing key features of differing approaches to the study of social movements in general and global social movements more specifically. This provides the context for exploring their relevance to the analysis of the experiences and achievements of Jubilee 2000. The evidence comes from published sources and discussion papers and from interviews with particular individuals involved, as staff and activists, in Jubilee 2000 itself and its constituent organizations.