Reduzindo colisões em redes locais sem fio através do alargamento das janelas de contenção por encurtamento dos slots e da divisão de tempo

Orientadora: Profa. Dra. Michele Nogueira LimaDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Informática. Defesa: Curitiba, 28/03/2017Inclui referências : p. 79-86Resumo: As Redes Locais Sem Fio (RLSF) são uma das principais formas de acesso à rede mundial de computadores na atualidade, presentes em praticamente todos os grandes centros urbanos. Contudo, a próxima geração de RLSF terá que prover protocolos de acesso ao meio escaláveis o suficiente para suportar a grande quantidade de dispositivos Wi-Fi esperada para os próximos cinco anos. Isto, porém, tem se mostrado um grande desafio, pois resultados de pesquisas indicam que o mecanismo atual de acesso ao meio destes dispositivos utiliza um processo de contenção ineficaz em ambientes com muitos usuários, tais como estádios e locais de eventos (redes densas). Este processo de contenção visa impedir que transmissões simultâneas, provenientes de diferentes terminais, causem interferências entre si, retendo-as em uma janela de tempo e liberando-as de forma controlada. Com isto, pretende-se aliviar a degradação do desempenho da rede causada por estas interferências. No entanto, os estudos publicados sobre o tema mostram que isto tem sido pouco eficaz à medida que a quantidade de transmissores concorrentes aumenta. Buscando uma solução para tal problema, este trabalho analisa e explora a proposta de alargamento das janelas de contenção através da redução da duração dos slots, a ser implementada pela futura emenda 802.11ax. Esta proposta tem o objetivo de mitigar as falhas de acesso ao meio, existentes no padrão atual, quando aplicado em redes densas. A mudança deve melhorar o desempenho da próxima geração de RLSF nestes cenários densos, o que é um dos objetivos da nova emenda. A análise aqui apresentada considera as diferentes classes de tráfego, ponderando as categorias de acesso para priorização de dados e suas respectivas janelas. O modelo matemático desenvolvido permite estimar as taxas de colisões de acordo com a densidade da rede. Os resultados de simulação indicam que a proposta atenua o problema das colisões inerentes ao processo de contenção e diminui a probabilidade de descartes de quadros. O estudo demostra os benefícios que a mudança alcança em termos de aumento da taxa de transferência e redução das retransmissões e também alerta para o seu possível impacto no processo de verificação do canal. Além do mais, a pesquisa aponta formas de melhorar a proposta em estudo para o 802.11ax, através de mecanismos de divisão de tempo que potencializam os seus ganhos em desempenho. Os resultados apresentam formas de aperfeiçoamento da solução, contribuindo com a literatura e assistindo no avanço da próxima geração de RLSF. Palavras-chave: 802.11ax, Protocolos MAC, Acesso ao Meio, Janela de Contenção.Abstract: Wireless Local Area Networks (WLAN) are one of the main means of Internet access, present in virtually all major urban centers. However, the next generation of WLAN will have to provide medium access protocols scalable enough to support the large number of Wi-Fi devices expected over the next five years. But, this has been proven to be a major challenge. As research results state, the current medium access mechanism of these devices uses an inefficient contention process when applied in environments with many users, such as stadiums and event locations (dense networks). This process aims to prevent simultaneous transmissions from different terminals to avoid interference among them. It holds transmissions in a time window and releases them in a controlled way. Thus, this has intended to reduce the network performance degradation caused by these interferences. However, published studies on the subject show that this has been ineffective as increases the number of concurrent transmitters. Looking for a solution to this problem, this research analyzes and explores the proposal of contention windows enlargement through time slots reduction, to be implemented in the future 802.11ax amendment. The purpose of this proposal is to mitigate medium access failures, present in the current standard when it is applied in dense networks. This change must improve the performance of the next generation WLAN in these dense scenarios, which is one of the goals on the new amendment. Our analysis considers the different classes of traffic, reflecting on the access categories for data prioritization and their respective windows. A mathematical model was developed to estimate the collision rates accordingly to the network density. Simulation results indicate that the proposal reduces collisions issues inherent to the backoff procedure, and it decreases the frame loss. Our study shows the improvements achieved by this proposal as increased throughput and reduced retransmissions and also it warns to the impact on the clear channel assessment process. Further, the research points out how to improve the proposal, through time division mechanisms that potentiate their gains in performance. The results present ways of improving the solution, contributing to the literature and assisting in the advance of the next generation WLAN. Keywords: 802.11ax, MAC Protocols, Backoff, Contention Window

Characterization, Avoidance and Repair of Packet Collisions in Inter-Vehicle Communication Networks

This work proposes a combined and accurate simulation of wireless channel, physical layer and networking aspects in order to bridge the gaps between the corresponding research communities. The resulting high fidelity simulations enable performance optimizations across multiple layers, and are used in the second part of this thesis to evaluate the impact of fast-fading channel characteristics on Carrier-Sense Multiple Access, and to quantify the benefit of successive interference cancellation

Characterization, Avoidance and Repair of Packet Collisions in Inter-Vehicle Communication Networks

This work proposes a combined and accurate simulation of wireless channel, physical layer and networking aspects in order to bridge the gaps between the corresponding research communities. The resulting high fidelity simulations enable performance optimizations across multiple layers, and are used in the second part of this thesis to evaluate the impact of fast-fading channel characteristics on Carrier-Sense Multiple Access, and to quantify the benefit of successive interference cancellation

Systematic Approaches for Telemedicine and Data Coordination for COVID-19 in Baja California, Mexico

Conference proceedings info: ICICT 2023: 2023 The 6th International Conference on Information and Computer Technologies Raleigh, HI, United States, March 24-26, 2023 Pages 529-542We provide a model for systematic implementation of telemedicine within a large evaluation center for COVID-19 in the area of Baja California, Mexico. Our model is based on human-centric design factors and cross disciplinary collaborations for scalable data-driven enablement of smartphone, cellular, and video Teleconsul-tation technologies to link hospitals, clinics, and emergency medical services for point-of-care assessments of COVID testing, and for subsequent treatment and quar-antine decisions. A multidisciplinary team was rapidly created, in cooperation with different institutions, including: the Autonomous University of Baja California, the Ministry of Health, the Command, Communication and Computer Control Center of the Ministry of the State of Baja California (C4), Colleges of Medicine, and the College of Psychologists. Our objective is to provide information to the public and to evaluate COVID-19 in real time and to track, regional, municipal, and state-wide data in real time that informs supply chains and resource allocation with the anticipation of a surge in COVID-19 cases. RESUMEN Proporcionamos un modelo para la implementación sistemática de la telemedicina dentro de un gran centro de evaluación de COVID-19 en el área de Baja California, México. Nuestro modelo se basa en factores de diseño centrados en el ser humano y colaboraciones interdisciplinarias para la habilitación escalable basada en datos de tecnologías de teleconsulta de teléfonos inteligentes, celulares y video para vincular hospitales, clínicas y servicios médicos de emergencia para evaluaciones de COVID en el punto de atención. pruebas, y para el tratamiento posterior y decisiones de cuarentena. Rápidamente se creó un equipo multidisciplinario, en cooperación con diferentes instituciones, entre ellas: la Universidad Autónoma de Baja California, la Secretaría de Salud, el Centro de Comando, Comunicaciones y Control Informático. de la Secretaría del Estado de Baja California (C4), Facultades de Medicina y Colegio de Psicólogos. Nuestro objetivo es proporcionar información al público y evaluar COVID-19 en tiempo real y rastrear datos regionales, municipales y estatales en tiempo real que informan las cadenas de suministro y la asignación de recursos con la anticipación de un aumento de COVID-19. 19 casos.ICICT 2023: 2023 The 6th International Conference on Information and Computer Technologieshttps://doi.org/10.1007/978-981-99-3236-

Performance Analysis For Wireless G (IEEE 802.11 G) And Wireless N (IEEE 802.11 N) In Outdoor Environment

This paper described an analysis the different capabilities and limitation of both IEEE technologies that has been utilized for data transmission directed to mobile device. In this work, we have compared an IEEE 802.11/g/n outdoor environment to know what technology is better. the comparison consider on coverage area (mobility), through put and measuring the interferences. The work presented here is to help the researchers to select the best technology depending of their deploying case, and investigate the best variant for outdoor. The tool used is Iperf software which is to measure the data transmission performance of IEEE 802.11n and IEEE 802.11g

Performance analysis for wireless G (IEEE 802.11G) and wireless N (IEEE 802.11N) in outdoor environment

This paper described an analysis the different capabilities and limitation of both IEEE technologies that has been utilized for data transmission directed to mobile device. In this work, we have compared an IEEE 802.11/g/n outdoor environment to know what technology is better. The comparison consider on coverage area (mobility), throughput and measuring the interferences. The work presented here is to help the researchers to select the best technology depending of their deploying case, and investigate the best variant for outdoor. The tool used is Iperf software which is to measure the data transmission performance of IEEE 802.11n and IEEE 802.11g