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Santa Rita do Sapucai, Brazil

Rabelo G.S.,Brazilian Labor Public Ministry MPT | Yacoub M.D.,University of Campinas | De Souza R.A.A.,National Institute of Communications of Brazil
IEEE Transactions on Vehicular Technology

Correlation among channels is a physical phenomenon that affects the performance of a wireless communication system and that cannot be neglected in a myriad of realistic fading scenarios. Providing computable mathematical means to better characterize the corresponding statistics is certainly of interest to any design engineer. In this context, this paper further extends the statistical correlation investigations of the α-μ fading model, presenting a new, exact, and easily computable series-type formulation for the multivariate α-μ joint cumulative distribution function (JCDF). Along with this general result and capitalizing on practical assumptions, an alternative, simpler formulation for the α-μ multivariate joint density function and its corresponding distribution function are also provided. These formulations are still general and yet compact, assuming arbitrary fading parameters and correlations among the marginal variates. An important feature of the series-type distribution is that any truncation version of it is a valid distribution. As an application example, the truncated series-based outage probability of the selection combining scheme is computed and compared with that obtained by means of numerical methods and simulations. The results show that a small number of terms of the series are sufficient to provide excellent agreement between approximate and exact results. © 2011 IEEE. Source

Beltran-Mejia F.,University of Campinas | Beltran-Mejia F.,National Institute of Communications of Brazil | Biazoli C.R.,University of Campinas | Cordeiro C.M.B.,University of Campinas
Optics Express

The sensitivity of an optical fiber microsensor based on inter-modal interference can be considerably improved by tapering a short extension of the multimode fiber. In the case of Graded Index fibers with a parabolic refractive index profile, a meridional ray exhibits a sinusoidal path. When these fibers are tapered, the period of the propagated beam decrease down-taper and increase up-taper. We take advantage of this modulation -along with the enhanced overlap between the evanescent field and the external medium- to substantially increase the sensitivity of these devices by tuning the sensor's maximum sensitivity wavelength. Moreover, the extension of this device is reduced by one order of magnitude, making it more propitious for reduced space applications. Numerical and experimental results demonstrate the success and feasibility of this approach. © 2014 Optical Society of America. Source

De Souza R.A.A.,National Institute of Communications of Brazil | Yacoub M.D.,University of Campinas
IEEE Transactions on Wireless Communications

An infinite series formulation for the multivariate - joint probability density function with arbitrary correlation matrix and non-identically distributed variates is derived. The expression is exact and general and includes all of the results previously published in the literature concerning the distributions comprised by the α-μ distribution. The general expression is then particularized to an indeed very simple, approximate closed-form solution. In addition, a multivariate joint cumulative distribution function is obtained, again in simple, closed-form manner. As an application example, the exact and approximate performances of the selection combining scheme given in terms of the outage probability is shown. Approximate and exact results are very close to each other for small as well as medium values of correlation. © 2006 IEEE. Source

Alberti A.M.,National Institute of Communications of Brazil
Journal of the Brazilian Computer Society

Nowadays, research initiatives to redesign the Internet are popping up around the world. Each of these projects has a particular focus and its own set of design requirements and key technologies. The panorama shows a wide diversity of pre-requirements and arguments, some very specific and superficial, others more general and deep. Despite this diversity, a conceptual-driven analysis of such scenario could reveal the current state-of-the-art on future Internet research, the common aspects that permeate all initiatives, and the open issues to be addressed in future work. This paper provides a comprehensive overview of the contemporary research from an abstract point of view, covering the design requirements and ingredients that are being adopted, interrelating, and analyzing them. © 2013 The Brazilian Computer Society. Source

Alberti A.M.,National Institute of Communications of Brazil
Studies in Computational Intelligence

The Internet became an extraordinary artifact for information exchanging, and it is now being considered a strategic infrastructure even for countries development. However, its success has fueled an upward spiral of new applications, which require increasingly intensive use of its capabilities, putting a lot of pressure on a design originally drawn for a scenario remarkably different from the current one. Concerned with actual Internet evolution and its limitations towards a future global information infrastructure, many research initiatives started to reinvent or rethink Internet, so it can fully assume the role we are assigning to it. This text discusses technological requirements, challenges and trends towards future network architectures. It covers latest new Internet design approaches and their main innovations. © 2010 Springer-Verlag Berlin Heidelberg. Source

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