VII International Telecommunications Symposium

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Rank codes – the State of Art
Ernst M. Gabidulin

DOI: 10.14209/sbrt.2010.1
Keywords: rank metric matrix rank code vector rank code random rank error rank row erasure rank column erasure fast decoding algorithm space-time code network coding public-key cryptography
Abstract
The State of Art for rank codes is presented. The theory and applications are considered.

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Capacity of CSMA under Nakagami Fading
Elvio J. Leonardo, Michel D. Yacoub

DOI: 10.14209/sbrt.2010.2
Keywords: Wireless communication CSMA Nakagami fading
Abstract
This paper investigates the throughput performance of carrier sense multiple access (CSMA) in a packet radio network and Nakagami fading environment. The approach considered includes the signal capture model with incoherent addition of interfering signals. The cases of uniform attenuation for all terminals (or perfect power control) as well as unequal average power levels are studied. Analytical and numerical results are presented.

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Ascending chain of semigroup rings and encoding
Tariq Shah, Atlas Khan, Antonio Aparecido de Andrade

DOI: 10.14209/sbrt.2010.3
Keywords: Semigroup ring BCH code alternant code Goppa code Srivastava code
Abstract
Let B be any finite commutative ring with identity. · · · ⊂ B[X; 1ak Z0] · · · ⊂ B[X; a12 Z0] ⊂ B[X; a1 Z0], where a ∈ {2, 3, 5, 7, · · ·}, k ≥ 1, is the descending chain of commutative semigroup rings. All these semigroup rings are containing the polynomial ring B[X; Z0]. In this paper initially we introduced the construction technique of cyclic codes through a semigroup ring B[X; 1 ak Z0] instead of a polynomial ring. After this we separately considered BCH, alternant, Goppa, Srivastava codes and by this new constructions we improve the several results of [1] by adopting the same lines as in [1].

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A New Model for VoIP Traffic Generation
Carlos Ignacio de Mattos, Eduardo Parente Ribeiro, Carlos Marcelo Pedroso

DOI: 10.14209/sbrt.2010.4
Keywords: Traffic Models Voice over IP Voice Codecs
Abstract
In this work a new model for VoIP traffic generation is proposed. The innovation of this model consists in modeling the user behavior instead of the aggregated traffic. We have analyzed the call holding time and the time interval between calls to characterize the user behavior. In order to provide an accurate packet generation, the data nature was modeled by identifying the time for packet transmission and the time interval between packets. Those variables of the proposed model were characterized with probability distributions. The parameters of the distributions were obtained with the analysis of real data collected from two major Brazilian telecommunications carriers. A VoIP traffic simulator was implemented and its results were compared with real data to validate the model. The similarity between synthetic and real data indicates that our model works properly and can be used for VoIP networks modeling and workload generation.

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Mobile Station Location using Genetic Algorithm Optimized Radio Frequency Fingerprinting
Rafael Saraiva Campos, Lisandro Lovisolo

DOI: 10.14209/sbrt.2010.5
Keywords: Mobile Station Location Radio Frequency Fingerprints Propagation Modeling Genetic Algorithms First Generation Population Correlation Space
Abstract
Radio Frequency Fingerprinting estimates the mobile station location by comparing a measured radio frequency fingerprint with a set of previously collected or generated reference fingerprints. This set is referred to as the search or correlation space. Genetic algorithms can be used to optimize both the location accuracy and the time required to produce a position fix, reducing the size of the search space. This paper proposes an innovation in such application of genetic algorithms, restricting the first generation population to the predicted best server area of the serving sector measured by the mobile station. In field tests in a GSM cellular network in a dense urban environment, this approach achieved reductions of 20% and 15% in the 50-th and 90-th percentile location errors, respectively, in comparison to the original formulation, where the initial population is randomly distributed throughout the whole service area. An average reduction of 91% in the time to produce a position fix was also observed

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A Traffic Policing Mechanism for Wimax Systems Based on Multifractal Modeling
Josemar A. Santos Jr, Flávio G. C. Rocha, Flávio H. T. Vieira

DOI: 10.14209/sbrt.2010.6
Keywords: Multifractal Traffic IEEE 802.16 Policing algorithms Wireless Traffic
Abstract
In this paper, we analyze the queueing performance in terms of loss rate of an OFDM (Orthogonal FrequencyDivision Multiplexing)/TDMA(Time Division Multiplexing Access) based Wimax system taking into account the multifractal behavior of the wireless traffic flows. To this end, first, we show evidences of multifractal characteristics on wireless traffic traces. These findings motivated us to propose a traffic policing and control scheme based on a multifractal envelope process in order to maintain the traffic flows wellbehaved, i.e., in accordance to the desired parameters. Simulations and comparisons to other methods are carried out to verify the efficiency of the proposed traffic policing.

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Mean Weight Behavior for the Generalized Subband Decomposition LMS Algorithm
Javier E. Kolodziej, Orlando J. Tobias, Rui Seara

DOI: 10.14209/sbrt.2010.7
Keywords: Averaging principle least-mean-square (LMS) algorithm mean weight behavior subband adaptive filters
Abstract
This paper presents an improved stochastic model for the generalized subband decomposition least-mean-square (GSD-LMS) algorithm. This algorithm is used as an alternative to the standard LMS aiming to improve the convergence speed under correlated input data. An analytical model for the first moment of the adaptive filter weights is derived considering just the independence between weight and input data vectors. Numerical simulation results confirm the accuracy of the proposed model, outperforming other models presented previously in the literature.

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Lossless Multi-Grid Chain Code with Optimized Cell Usage for Contour Description of Visual Objects
Fabiana O. P. Fernandes, Willian G. de Almeida, Flávia M. Freitas, Abraham Alcaim

DOI: 10.14209/sbrt.2010.8
Keywords: shape encoding object-based image compression MPEG-4 chain code grid cell
Abstract
In the context of object-based image compression, shape encoders that describe the contour of the objects, called chain codes, tend to be more efficient than that the one based on bitmap, which is the MPEG-4 Part 2 framework. Among the chain codes, those based on grid cells are expected to outperform the ones that employ a symbol to code each particular boundary pixel. This paper presents a lossless chain code based approach for binary shapes encoding, called OCULMGCC (Optimized Cell Usage - Lossless Multi Grid Chain Code). The OCU-LMGCC solves shortcomings in the original MGCC, optimizes the required extra parallel information to the decoder and uses a new set of coding symbols, better suited to the novel cell-switching schemes proposed. Results showed a compression gain noticeable larger than the known algorithms reported in the literature.

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An Adequate Objective Performance Evaluation of Dirac Video Codec Compared to H.264/AVC
André F. de Araujo, Yuzo Iano, Rangel Arthur

DOI: 10.14209/sbrt.2010.9
Keywords: Dirac video codec H.264; Video Coding Vide Compression Wavelet-based video coding
Abstract
Dirac, a relevant new open wavelet-based video codec, has been released recently. The main contribution of this paper is an adequate performance evaluation of this codec compared to the well-known H.264/AVC. This work differs significantly from previous ones which present unfair and inconclusive comparisons. Eight videos comprising three different resolutions with various degrees and kinds of motion are used to perform the simulations, as well as appropriate tuning of coding parameters for both codecs. In every case, H.264’s objective visual quality results outperform Dirac ones, but some evidences indicate Dirac might provide better subjective quality.

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Providing Higher Entropy Cryptographic Keys by the Use of Biometrics
D. P. B. A. Camara, V. C. da Rocha Jr.

DOI: 10.14209/sbrt.2010.10
Keywords: Biometrics cryptography error-correcting codes security
Abstract
In this paper modifications are investigated to a previously introduced Key Regeneration system used to obtain cryptographic keys from biometric data, specifically from the iris. These modifications improve the performance of the previous system making possible the regeneration of longer and higher entropy cryptographic keys. The modified system was evaluated on two public databases: CBS-BiosecureV1 and NIST-ICE 2005. On NIST-ICE 2005 it is possible to regenerate a 287 binary digit cryptographic key with an estimated entropy of 231 bits at 0.28% False Acceptance Rate (FAR) and 6.30% False Rejection Rate (FRR). The cryptographic keys regenerated possess enough length and entropy to be used on practical cryptosystems like, for example, the AES.

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