National Institute of Communications of Brazil

Santa Rita do Sapucai, Brazil

National Institute of Communications of Brazil

Santa Rita do Sapucai, Brazil
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Da Silva A.P.T.R.,National Institute of Communications of Brazil | Brito J.M.C.,National Institute of Communications of Brazil
International Conference on Information Networking | Year: 2017

Systems comprised of Cognitive Radio Networks (CRN) have been gaining attention in the current literature, given their ability to reduce spectrum scarcity by reusing parts of the spectrum band, while at the same time ensuring a minimum Quality of Service (QoS) margin. In this regard, it becomes important to consider the CRN's usage of multiple access protocols. In this paper, we consider a CRN with the Slotted Aloha protocol, and in order to improve the system's performance, we also proposed the use of an adaptive modulation technique. Finding the optimum switching points between neighboring modulations is a key issue of the adaptive modulation system. Thus, we investigated the optimum switching points through the maximum throughput criterion for a primary and secondary network considering the Capture Effect and the interference between primary and secondary users. © 2017 IEEE.

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 | Year: 2011

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.

Alberti A.M.,National Institute of Communications of Brazil
Communications in Computer and Information Science | Year: 2012

Currently, there are many proposals to redesign the Internet. While some design ingredients are common to several approaches, the way they are adopted and combined usually differs from proposal to proposal. This paper defends the argument that a deeper architectural rethinking requires a deeper search for synergies among the selected ingredients. It argues that this is fundamentally a possible path to simplify the design, since ingredients are homogenized towards more coherent blueprints. The paper explores raised synergies in a conceptual way and proposes some guidelines to help designing accordingly. © 2012 Springer-Verlag.

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 | Year: 2014

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.

Guimaraes D.A.,National Institute of Communications of Brazil | Aquino G.P.,National Institute of Communications of Brazil
Sensors (Switzerland) | Year: 2015

Recently, a novel resource-efficient technique for the reporting channel transmissions in cooperative spectrum sensing was proposed. In this technique, secondary users are allowed to simultaneously send their local decisions to the fusion center, saving time and frequency resources. Expressions for the probabilities of detection and false alarm for the unitary-gain AWGN reporting channels were derived, while simulation results were given for both the AWGN and Rayleigh fading channels. Here, we provide an expression that is applicable to AWGN channels with different real-valued gains and to time-varying real-valued gains. A simple suboptimum receiver is proposed for the general complex-valued fading and non-fading channels, with an improved performance in the low signal-to-noise ratio condition. Numerical results are shown for both the AWGN and Rayleigh fading reporting channels, demonstrating the accuracy of the derived expressions and the attractive performance of the proposed receiver. © 2015 by the authors; licensee MDPI, Basel, Switzerland.

De Souza R.A.A.,National Institute of Communications of Brazil | Yacoub M.D.,University of Campinas
IEEE Transactions on Wireless Communications | Year: 2010

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.

Alberti A.M.,National Institute of Communications of Brazil
Journal of the Brazilian Computer Society | Year: 2013

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.

Cogliatti R.,National Institute of Communications of Brazil | De Souza R.A.A.,National Institute of Communications of Brazil | Yacoub M.D.,University of Campinas
IEEE Communications Letters | Year: 2012

In this letter, we propose a simple and highly efficient random sequence generator for κ-μ and η-μ variates and a near-100% efficient algorithm for generating α-μ variates. The proposed algorithm may yield an efficiency higher than 80% for η-μ, 87.5% for κ-μ and almost 100% for α-μ. These generators are implemented via the rejection technique and allow for arbitrary fading parameters. The goodness-of-fit is objectively measured using the the p-value of the KolmogorovSmirnov test. © 2012 IEEE.

Brito J.M.C.,National Institute of Communications of Brazil
2016 International Multidisciplinary Conference on Computer and Energy Science, SpliTech 2016 | Year: 2016

It is expected that the fifth generation (5G) of mobile networks will be standardized in 2020. For this new generation, there are several new performance requirements in addition to higher data rates. E-health and the Internet of Things (IoT) are two important applications that define the new requirements. In this paper, we discuss several technological trends in wireless communications towards 5G networks, highlighting the influence of e-health and IoT applications. © 2016 University of Split, FESB.

Alberti A.M.,National Institute of Communications of Brazil
Studies in Computational Intelligence | Year: 2010

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.

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