AUTOMATIC ASSINCHRONOUS VIDEO DEMULTIPLEXING

Marcelo Hor-Meyll Alvares, Rafael Dueire Lins

DOI: 10.14209/sbrt.2010.66

Keywords: demultiplexing video forensics

Abstract

The work on real forensics videos involving banking images lead to the method presented here: a software approach to the problem of demultiplexing time multiplexed security videos. This approach is of particular interest in cases in which, for some reason, the regular demultiplexing hardware/software is not available. Based on comparisons of the mean frame luminance and having low frequency characteristics of the scenes as references, this approach is being used with good results by video experts in Brazil to help locating sequences of particular interest in surveillance time multiplexed videos recorded in magnetic video cassettes.

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Efficiently Generating Digital Libraries of Proceedings with The LiveMemory Platform

Rafael Dueire Lins, Gabriel de Pereira e Silva, Gabriel Torreão, Neide F. Alves

DOI: 10.14209/sbrt.2010.67

Keywords: digital libraries proceedings document engineering document processing

Abstract

The proceedings of many technical events in different areas of knowledge witness the history of the development of that area. This paper describes LiveMemory, a user friendly software platform designed to generate digital libraries of proceedings.

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Close Approximations for Daublets and their Spectra

V. Vermehren V., J. E. Wesen, H. M. de Oliveira

DOI: 10.14209/sbrt.2010.68

Keywords: Wavelets compactly support Fourier Scalogram OFDM

Abstract

This paper offers a new regard on compactly supported wavelets derived from FIR filters. Although being continuous wavelets, analytical formulation are lacking for such wavelets. Close approximations for daublets (Daubechies wavelets) and their spectra are introduced here. The frequency detection properties of daublets are investigated through scalograms derived from these new analytical expressions. These near-daublets have been implemented on the MatlabTM wavelet toolbox and a few scalograms presented. This approach can be valuable for wavelet synthesis from hardware or for application involving continuous wavelet-based systems, such as wavelet-OFDM.

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Performance Analysis of HARQ in WiMAX Networks Considering Imperfect Channel Estimation

Ricardo V. Dias, João P. Leite, Rafhael M. Amorim, André N. Barreto, Paulo Henrique P. de Carvalho, Robson D. Vieira

DOI: 10.14209/sbrt.2010.69

Keywords: channel estimation HARQ incremental redundancy WiMAX

Abstract

Hybrid Automatic Repeat Query (HARQ) is an error correction technique that has become an integral part of most current broadband wireless standards such as IEEE 802.16 and 3GPP-LTE (Long Term Evolution). Although extensive studies have been made on the performance of HARQ, they usually assume perfect channel state information at the receiver. This paper addresses the performance of incremental redundancy HARQ under the specifications of the physical layer of the WiMAX standard considering imperfect channel state information, such as the one obtained by channel estimation. Several combinations of modulation, channel code rates and information block size are considered, and a realistic physical channel model used for standardization is used throughout the simulations to evaluate the performance of HARQ. Results show that the link throughput can be severely degraded, specifically at low values of signal-to-noise ratio, and HARQ performance may be too optimistic if channel estimation is ignored.

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Demonstrating the security vulnerabilities of the Identity-based Key Management scheme for MANETs

Eduardo da Silva, Murilo Soares Lima, Luiz Carlos P. Albini

DOI: 10.14209/sbrt.2010.70

Keywords: Key Management Security Attacks MANETs

Abstract

The next generation of mobile communications will merge the well-known infrastructured wireless networks and the infrastructureless mobile ad hoc networks. However, their natural characteristics make them vulnerable to numerous severe attacks, making security a major issue in such networks. Cryptography mechanisms, both symmetric and asymmetric, provide strong techniques against most vulnerabilities. Among the asymmetric ones, the Identity-Based (IDbased) cryptographic mechanisms are proposed to simplify key management and to reduce the memory storage cost. In IDbased schemes, the node or user identity is used as its public key, while the private key is still provided by an external entity. Among all ID-based key management schemes found in the literature, the Identity-based key management (IKM) is the most suitable for the mobile ad hoc networks environment. However, IKM does not consider the presence of malicious nodes in the system. This paper analyses the IKM operations, evaluating its communication performance and its effectiveness in scenarios under false accusation attacks. Results show that IKM is not efficient in terms of communication costs neither resistant to false accusation attacks.

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Removing Back-to-Front Interference in Documents with Mirror Filtering

R. D. Lins, I. G. da Silva Netto

DOI: 10.14209/sbrt.2010.71

Keywords: Back-to-front interference Bleeding

Abstract

Very often documents are written on both sides on translucent paper making visible the ink from one side on the other. This artifact was called “back-to-front interference”. The direct binarization of documents with such interference yields unreadable documents. A mirror transformation to remove such noise was suggested over a decade ago, but there is no record in the literature either on how to implement it or of its effectiveness. This paper proves viable the mirror transformation method for generating high-quality monochromatic images of documents with back-to-front interference.

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Blocking-Effect Reduction in a Reversed-Complexity Video Codec Based on a Mixed-Quality Framework

Edson M. Hung, Ricardo L. de Queiroz

DOI: 10.14209/sbrt.2010.72

Keywords: Video codec reversity-complexity blocking-effect overlapped motion compensation

Abstract

This paper presents a blocking-effect reduction in a method for reversed-complexity video codec. We used intra predicted frames encoded at different quality (distortion) targets. We propose a technique to improve the enhancement layer of a mixed-quality encoded sequence, using information from the high-quality (key) frames to enhance the low-quality (non-key) ones at the decoder. The results show that it is possible to subjectively reduce the blocking effect by using overlapped motion compensation at the enhancement layer. It is shown that the subjective quality is improved and the objective quality is incremented at the non-key frames.

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EGPRS2 Deployment as a Resource-saving Feature for Voice

A. J. Loureiro, R. F Iida

DOI: 10.14209/sbrt.2010.73

Keywords: GERAN Evolution EGPRS EGPRS2 spectrum efficiency resources saving

Abstract

EGPRS2 is part of the GERAN evolution standardized in 3GPP GERAN Release 7 and it allows higher throughput rates per timeslot due to the adoption of higher order modulation, higher symbol rate, turbo codes and spectrally wide pulse shape. Another possibility for EGPRS2 adoption by operators is to keep the existing EGPRS throughput rates using less network resources. EGPRS2 with higher spectrum efficiency and higher number of multiplexed users per timeslot can lead to lower PDTCH utilization. EGPRS2 deployment can lead to resource savings, which in turn can be used to increase the voice quality/capacity or can be used to refarm spectrum to WCDMA/HSPA/LTE networks. This paper shows how EGPRS2 adoption can provide voice gains in a regular scenario where PDTCH resources can be saved. EGPRS with 4 PDTCH is compared with EGPRS2 using 3 PTDCH.

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Cyclotomic Basis for Computing the Discrete Fourier Transform

G. Jerônimo da Silva Jr., R. M. Campello de Souza

DOI: 10.14209/sbrt.2010.74

Keywords: FFT DFT multiplicative complexity cyclotomic basis

Abstract

This paper presents a new fast algorithm for computing an N-point discrete Fourier transform. The algorithm meets the Heideman multiplicative complexity lower bound for N = {3, 4, 6, 8, 12} and is based upon the decomposition of the elements of the transform matrix into a cyclotomic basis.

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HMM Modeling of Burst Error Channels by Particle Swarm Optimization of the Likelihood Function

M. Vinicius dos Santos, Ernesto L. Pinto, Marco Grivet

DOI: 10.14209/sbrt.2010.75

Keywords: Hidden Markov models Fritchman models ML estimation PSO

Abstract

This paper proposes a new strategy for fitting Hidden Markov Models to error processes of channels with memory. Our approach consists of obtaining the analytical expression of the likelihood function of the model parameters and applying particle swarm optimization (PSO) to obtain their maximum likelihood (ML) estimates. In particular, this approach is here applied to the well known single error-state (simplified) Fritchman models, which have been recognized as a very useful tool for modeling error process of several communications systems over the last decades. The paper also addresses the mathematical analysis of several statistics of burst errors produced by these models. Some numerical examples are given in order to illustrate the effectiveness of the approach here proposed.

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