Walter Godoy

Particle Swarm Optimization for the Multidimensional Knapsack Problem

The multidimensional 0/1 knapsack problem is a classical problem of discrete optimization. There are several approaches for solving the different variations of such problem, including mathematical programming and stochastic heuristic methods. This paper presents the application of Particle Swarm Optimization (PSO) for the problem, using selected instances of ORLib. For the instances tested, results were very close or equal to the optimal solution known, even considering that the parameters of PSO were not optimized. The analysis of the results suggests the potential of a simple PSO for this class of combinatorial problems.

On the impact of active queue management on VoIP quality of service

In this paper, we assess the impact of active queue management (AQM) on the quality of service of voice over IP (VoIP). Some of the most representative AQM schemes are analyzed through extensive simulations; evaluating its effect on the perceived quality of voice calls. We investigate different network scenarios, changing network loads and scheme control parameters. Network impairments are related to user perception by means of well known algorithmic models, expressing user satisfaction in the MOS scale. Our main results shows that the use of active queue management schemes significantly improve the perceived quality of voice calls, offering adequate user satisfaction.

A new approach to the information set decoding algorithm

An efficient suboptimal soft-decision decoding algorithm for block codes, called the modified information set algorithm with real time information set generation, is presented. In this algorithm the information provided by soft decisions are used to generate, in real time, the information sets used in the decoding. Moreover, a new high performance stop rule, called the sum rule, is used to reduce the number of information sets generated. The algorithms performance is also evaluated by computer simulation.

A novel DWT-SVD video watermarking scheme using side view

In this paper, we propose a new method that use side view video pre-processing with DWT-SVD based water-marking scheme. This processing switch the video references of the frames with dimensions equivalent of the number of frames like width and the same height than the original video. The DWT-SVD watermarking is applied in this video using a grayscale image inserted in Y(luminance) of the YUV. The experimental results showed that method have success to make the watermark imperceptible according to the PSNR metric and robust against noises addition, frames attacks and MPEG compression.

A Heuristic Algorithm Based on Ant Colony Optimization for Multi-objective Routing in Vehicle Ad Hoc Networks

Vehicle Ad hoc Network (VANET) provides an opportunity for innovation in the transportation area, enabling services for Intelligent Transportation System (ITS). Because of VANET features, such as highly dynamic networks topology and frequent discontinuity, it is desirable to establish, at a given moment, routes for fast delivery of messages, having a low probability of disconnection. This leads to a multiobjective problem. In this work we propose multiobjective heuristic algorithm, based on ACO (Ant Colony Optimization) to find routes considering the best commitment between the shortest path (number of nodes in a route) and the lowest probability of disconnection. Simulations were done with three different scenarios: static routing, static routing with obstacles, and dynamic routing. Results were very promising, obtained with small computational effort, and allowing the use of the algorithm for real-time optimization.

A proposal of a cryptography algorithm with techniques of error correction

A new cryptographic system is presented in this paper which combines error-correction techniques with cryptographic protection as secure as one might want. The proposed system is based on the following: given a linear block code (n, k), n > k, we have a lot of possibilities to distribute ‘k’ information symbols among ‘n’ symbols composing the code word. A method for the cryptanalysis of the system is also proposed. These possibilities increase when n ⪢ k and include the order and place of the T symbols among the ‘n’ symbols. Practical results were obtained via simulation on a PC486, 66 MHz, where the proposed system and its cryptographic analysis were implemented.Abstract A new cryptographic system is presented in this paper which combines error-correction techniques with cryptographic protection as secure as one might want. The proposed system is based on the following: given a linear block code (n, k), n > k, we have a lot of possibilities to distribute ‘k’ information symbols among ‘n’ symbols composing the code word. A method for the cryptanalysis of the system is also proposed. These possibilities increase when n ⪢ k and include the order and place of the T symbols among the ‘n’ symbols. Practical results were obtained via simulation on a PC486, 66 MHz, where the proposed system and its cryptographic analysis were implemented.

An Efficient Approach of Scheduling with Call Admission Control to Fixed WiMAX Networks

The major challenge for the second decade of this century is the implementation of access to high-speed internet, known as broadband internet. Thus, the IEEE (Institute of Electrical and Electronics Engineers) has developed a new standard for wireless access, called IEEE 802.16. Also known as WiMAX (Worldwide Interoperability for Microwave Access), it is an emerging technology for next generation wireless networks which supports a large number of users, both mobile and nomadic (fixed), distributed across a wide geographic area. Based on these assumptions, and considering that the standard does not specify a scheduling algorithm, a new scheduler with call admission control was proposed based on Latency-Rate (LR) server theory and with system characteristics as specified by the system standard using the WirelessMAN-OFDM (Orthogonal Frequency Division Multiplexing) air interface. The proposed scheduler calculates the time frame (TF) in order to maximize the number of stations allocated in the system while managing the delay required for each user. Properties of this proposal have been investigated theoretically and through simulations. The results of simulations show that an upper bound on the delay can be achieved for a large range of network loads, with bandwidth optimization.

Voice over IP quality of service using active queue management

This paper presents a comprehensive study about the impact of active queue management (AQM) on voice over Internet protocol (VoIP) quality of service. One of the most representative AQM scheme is analyzed through extensive simulation and its effect on the perceived quality of voice calls is evaluated. Different network scenarios, changing network loads and different scheme control parameters are investigated. Network impairments are related to user perception by means of well known algorithmic models, expressing user satisfaction in the MOS scale. The main results obtained show that the use of active queue management schemes like adaptive random early detection (ARED) significantly improve the perceived quality of voice calls.

Effective bandwidth based connection admission control for stored variable bit rate video streams

This paper proposes a novel admission control architecture for video-on-demand servers, which provide deterministic guarantees on the maximum delay of video traffic and increase the network resource utilization. The framework take advantage of the fact that stored video streams can be processed off-line to calculate the space and time parameters in order to estimate its effective bandwidth under the many sources asymptotic regime. The automatic generation of video data representation (packetized and encapsulated in network protocols) in textual format allows a full characterization of the underlying process so as to precisely calculate its bandwidth requirements. To bypass the traffic prediction problem, since the off-line estimation does not capture the exact dynamics of the video stream in the time domain, the link is divided into several virtual links, where only streams with same content are multiplexed (group multiplexing approach). The admission control is aided by a Database Management System, where a stored procedure decides whether to accept or reject a connection by simple compare the sum of effective bandwidths for the traffic streams with the available resources. The efficiency of the model is analyzed and compared with the deterministic approach. It achieves accuracy and high channel utilization.

A fast modular simulator for combinational logic circuits generated by genetic algorithm

This paper presents a structure for a fast generic simulator for combinational logic circuits, intended for use with genetic algorithm (GA) multi-objective optimization. A modular structure is proposed containing a chromosome translator layer, so to isolate the simulator from the idiosyncrasies of the chosen genetic codification. The simulator archieved high performance, considering its software-only implementation, and it was successfully used to generate valid circuits while integrated into a GA.