Hermínio S. Gomes

The Influence of Interference Networks in QoS Parameters in a WLAN 802.11g : a Bayesian Approach

In spite of the significant increase of the use of Wireless Local Area Network (WLAN) experienced in the last years, design aspects and capacity planning of the network are still systematically neglected during the network implementation. For instance, to determine the location of the access point (AP), important factors of the environment are not considered in the project. These factors become more important when several APs are installed, sometimes without a frequency planning, to cover a unique building. Faults such as these can cause interference among the cells generated by each AP. Therefore, the network will not obtain the QoS patterns required for each service. This paper proposes a strategy to determine how much a given network can affect the QoS parameters of another network, by interference. In order to achieve this, a measurement campaign was carried out in two stages: firstly with a single AP and later with two APs using the same channel. A VoIP application was used in the experiment and a protocol analyzer collected the QoS metrics. In each stage 46 points were measured , that are insufficient for statistically characterize the environment. For expanding this data, an Artificial Neural Network (ANN) was used. After the measurement, an analysis of the results and a set of inferences were made by using Bayesian Networks, whose inputs were the experimental data, i.e., QoS metrics like throughput, delay, jitter, packet loss, PMOS and physical metrics like power and distance.

Path loss model for densely arboreous cities in Amazon Region

This work proposes a propagation loss model for densely arboreous environment at 900 and 1800 MHz bands. In this model, the environment non-homogeneities and the base station antenna height effects are incorporated in the total loss. A measurement campaign was accomplished in three cities of the State of Para, Brazil, for validate the model.

Methodology for analysis of the coverage probability of WLAN using the padé approximant

This paper proposes a methodology for analysis of the signal reception probability in a 2.4GHz Wireless Local Area Network (WLAN). For validating this methodology a measurement campaign was carried out in an indoor environment using an access point as signal transmitter, and a notebook computer, equipped with a wireless board, as receiver. Twenty five average power received values were collected in this environment. Considering that the number of samples was insufficient for statistically characterize the environment, the colleted data was expanded using an Artificial Neural Network (ANN). The propagation loss was calculated using the expanded data in an adapted Pade Approximant model. It was included also, in the model, the number of obstacles intersected by the signal, as well as the loss due to each kind of obstacles. The obtained results were compared to a classical literature model.

Empirical study of the QoS parameters behavior of a VoIP application in wi-fi networks

The use of wireless local area networks (WLANs), as well as the proliferation of the use of multimedia applications has grown fast in recent years. Some factors affect the quality of service(QoS) received by the user. The interference is an example. This work presents an empirical study of the QoS parameters of a VoIP application in the presence of an interference network, as well as the relevance in the design of wireless networks to determine the range of an access point, taking into account several parameters as power, jitter, packet loss, delay and PMOS.

A WLAN planning proposal through computational intelligence and genetic algorithms hybrid approach

This paper proposes a WLAN planning strategy through the use of computational intelligence and genetic algorithm. A measurement technique was used to collect data from a real WLAN network. Metrics like power, distance, delay, jitter, packet loss, throughput and PMOS were analysed through the use of bayesian networks. Finally, to optimize the QoS parameters a genetic algorithm was applied to find the best distance from the AP to support the QoS ITU-T recommendations.

A Visualization Tool for Analyzing the Design of Physical and Network Layers Parameters of a Wireless Network

The use of wireless networks (WLANs, femtocells, Wimax), as well as the increasing use of multimedia applications have grown fast in recent years. Some factors affect the quality of service (QoS) received by the user such as interference. This paper presents a novel data visualization tool for performance evaluation of wireless networks aiding analysis and design of their networks, considering relevant parameters from both physical and network layers (power, jitter, packet loss, delay and PMOS). The performance evaluation is achieved in three steps: measurement, computational intelligence approach through Bayesian networks and mathematical model. The measurement was done implementing an empirical study of the quality of services (QoS) parameters of a VoIP application in the presence of an interference network. Thus, this work is based on a hybrid approach that considers measuring and conditional probability tables, generated from a Bayesian Network, applied to wireless networks, considering QoS parameters. In this work an indoor environment was used to be analyzed but other wireless networks can make use of this visualization tool.

The compromise with the covered area and the bit error rate in a suburban environment densely arboreous

In this paper a model is used for electromagnetic propagation waves in suburban environment densely arboreous to evaluate the covered efficiency of a cellular mobile communication system. The compromise with the covered area and the Bit Error Rate (BER) is identified as the key in the propagation characteristics that have the potential to influence the performance of the system. After that, the Bit Error Probability and the covered area is studies numerically for different heights of transmitter antenna. Experimental data had been gotten in one densely arboreous environment to adjust the considered model. Simulation for a GSM system had been carried through to evaluate the covered and the BER of the system and the results obtained indicate the performance of the system for the QoS requirement.

Empirical radio propagation model for DTV applied to non-homogeneous paths and different climates using machine learning techniques

The establishment and improvement of transmission systems rely on models that take into account, (among other factors), the geographical features of the region, as these can lead to signal degradation. This is particularly important in Brazil, where there is a great diversity of scenery and climates. This article proposes an outdoor empirical radio propagation model for Ultra High Frequency (UHF) band, that estimates received power values that can be applied to non-homogeneous paths and different climates, this last being of an innovative character for the UHF band. Different artificial intelligence techniques were chosen on a theoretical and computational basis and made it possible to introduce, organize and describe quantitative and qualitative data quickly and efficiently, and thus determine the received power in a wide range of settings and climates. The proposed model was applied to a city in the Amazon region with heterogeneous paths, wooded urban areas and fractions of freshwater among other factors. Measurement campaigns were conducted to obtain data signals from two digital TV stations in the metropolitan area of the city of Belém, in the State of Pará, to design, compare and validate the model. The results are consistent since the model shows a clear difference between the two seasons of the studied year and small RMS errors in all the cases studied.

New strategies for planning and performance evaluation of wireless networks: case studies based on the cross-layer approach

The use of wireless local area networks, called WLANs, as well as the proliferation of the use of multimedia applications have grown rapidly in recent years. Some factors affect the quality of service (QoS) received by the user and interference is one of them. This work presents strategies for planning and performance evaluation through an empirical study of the QoS parameters of a voice over Internet Protocol (VoIP) application in an interference network, as well as the relevance in the design of wireless networks to determine the coverage area of an access point, taking into account several parameters such as power, jitter, packet loss, delay, and PMOS. Another strategy is based on a hybrid approach that considers measuring and Bayesian inference applied to wireless networks, taking into consideration QoS parameters. The models take into account a cross layer vision of networks, correlating aspects of the physical environment, on the signal propagation (power or distance) with aspects of VoIP applications (e.g., jitter and packet loss). Case studies were carried out for two indoor environments and two outdoor environments, one of them displaying main characteristics of the Amazon region (e.g., densely arboreous environments). This last test bed was carried out in a real system because the Government of the State of Para has a digital inclusion program called NAVEGAPARA.

Vibration monitoring of electric generators without sensor dedicated

This paper describes a method for on-line condition monitoring of rotating electric generators without a need for installed sensors dedicated. This sensorless method has been based on continuous monitoring vibration using neural networks for the classification of bearing failures experimentally induced. The results obtained have an error of less than 0,5% confirming the validity of the method proposed.