Contributions to QoS and energy efficiency in wi-fi networks

The Wi-Fi technology has been in the recent years fostering the proliferation of attractive mobile computing devices with broadband capabilities. Current Wi-Fi radios though severely impact the battery duration of these devices thus limiting their potential applications. In this thesis we present a set of contributions that address the challenge of increasing energy efficiency in Wi-Fi networks. In particular, we consider the problem of how to optimize the trade-off between performance and energy effciency in a wide variety of use cases and applications. In this context, we introduce novel energy effcient algorithms for real-time and data applications, for distributed and centralized Wi-Fi QoS and power saving protocols and for Wi-Fi stations and Access Points. In addition, the di¿erent algorithms presented in this thesis adhere to the following design guidelines: i) they are implemented entirely at layer two, and can hence be easily re-used in any device with a Wi-Fi interface, ii) they do not require modi¿cations to current 802.11 standards, and can hence be readily deployed in existing Wi-Fi devices, and iii) whenever possible they favor client side solutions, and hence mobile computing devices implementing them can benefit from an increased energy efficiency regardless of the Access Point they connect to. Each of our proposed algorithms is thoroughly evaluated by means of both theoretical analysis and packet level simulations. Thus, the contributions presented in this thesis provide a realistic set of tools to improve energy efficiency in current Wi-Fi networks

Modelagem analítica da vazão de redes sem fio baseadas na norma IEEE 802.11ah

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Elétrica, 2018.Inúmeras tecnologias promissoras foram desenvolvidas desde a concepção da Internet das Coisas (IoT, do inglês Internet of Things) que poderão modificar diferentes aspectos em nosso cotidiano. Tendo em vista o rápido crescimento da IoT, foi criado o grupo de tarefa IEEE 802.11ah para o desenvolvimento de uma nova norma Wi-Fi para lidar com os principais desafios da IoT, que são a conectividade de muitos dispositivos com recursos de energia limitados a um único ponto de acesso e o aumento do alcance das transmissões para distâncias muito maiores do que aquelas tipicamente utilizadas em redes locais sem fio. Assim, esse padrão traz novos mecanismos nas camadas física e de enlace para atender aos requisitos da IoT. Na camada física, houve modificações para operação em faixas de frequências abaixo de 1 GHz e, na camada MAC, o padrão traz novos mecanismos de economia de energia para ter um melhor desempenho em redes densas, sendo um deles o acesso restrito ao canal (RAW, do inglês Restricted Access Window). Recentemente, há muitos trabalhos sobre o IEEE 802.11ah, entretanto, a maior parte deles trazem ideias de agrupamento ou modelagem analítica para descobrirem o tamanho ótimo do RAW para obter maior desempenho da rede. No entanto, para um melhor entendimento dos efeitos dos diversos parâmetros e mecanismos do IEEE 802.11ah, esta dissertação apresenta um modelo analítico da função de coordenação distribuída do IEEE 802.11ah para o caso em que as estações estão distribuídas uniformemente em diversos slots RAW e possuem a mesma prioridade de tráfego, sob condições de tráfego saturado e canal ideal. Em nosso modelo, consideramos que cada intervalo de beacon possui somente um RAW o qual é dividido em slots RAW, e estudamos o impacto no desempenho da vazão ao variar o número de slots RAW e o número de estações na rede. Além disto, introduzimos ao modelo Markoviano uma probabilidade de término do slot RAW e propomos duas expressões empíricas para o cálculo desta probabilidade. Por fim validamos o modelo analítico com simulações no simulador de redes NS3 e, a partir das simulações computacionais, encontramos uma constante de ajuste para aproximar o modelo das simulações.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).Many promising technologies have been developed since the conception of the Internet of Things (IoT) that can modify different aspects of our daily lives. In light of the rapid growth of IoT, it was created the IEEE 802.11ah Task Group to develop a newWi-Fi standard to address IoT’s key challenges, which are the connectivity of many devices with limited power resources to a single access point and the increase in the transmissions range for distances much greater than those typically used in wireless local area networks. Thus, this standard brings new mechanisms in the physical and link layers to meet IoT requirements. In the physical layer, there were modifications to permit the operation in frequency bands below 1 GHz and, in the MAC layer, the standard brings new power saving mechanisms to perform better in dense networks, one of which is the restricted access to the channel (RAW). Recently, there have been a lot of work on IEEE 802.11ah, however, most of them bring grouping or analytical modeling ideas to find out the optimal RAW size for a higher network performance. On the other hand, for a better understanding of the effects of the various IEEE 802.11ah parameters and mechanisms, this dissertation presents an analytical model of the distributed coordination function of IEEE 802.11ah for the case where the stations are evenly distributed in several RAW slots and have the same traffic priority, under conditions of saturated traffic and ideal channel. In our model, we consider that each beacon interval has only one RAW which is divided into RAW slots, and we study the impact on throughput performance by varying the number of RAW slots and the number of stations in the network. In addition, we introduce to the Markovian model a probability of reaching the end of a RAW slot and propose two heuristic expressions for this probability calculation. Finally we validate the analytical model with simulations in the networks simulator NS3 and, from the computational simulations, we find an adjustment constant to approximate the model of the simulations

Inter-Vehicle Communication at Intersections : An Evaluation of Ad-Hoc and Cellular Communication

This book evaluates the ability of ad-hoc and cellular communication to enable cross-traffic assistance at intersections. Potential issues like Non-Line-Of-Sight (NLOS) reception with ad-hoc and limited capacity, higher latency and costs with cellular technology are investigated in two individual evaluations. A method for efficient information delivery via cellular systems and an inter-vehicle NLOS radio propagation model are proposed. Finally, the suitability of both technologies is compared

Information Systems for Supporting Fire Emergency Response

Despite recent work on information systems, many first responders in emergency situations are unable to develop sufficient understanding of the situation to enable them to make good decisions. The record of the UK Fire and Rescue Service (FRS) has been particularly poor in terms of providing the information systems support to the fire fighters decision-making during their work. There is very little work on identifying the specific information needs of different types of fire fighters. Consequently, this study has two main aims. The first is to identify the information requirements of several specific members of the FRS hierarchy that lead to better Situation Awareness. The second is to identify how such information should be presented. This study was based on extensive data collected in the FRS brigades of three counties and focused on large buildings having a high-risk of fire and four key fire fighter job roles: Incident Commander, Sector Commander, Breathing Apparatus Entry Control Officer and Breathing Apparatus Wearers. The requirements elicitation process was guided by a Cognitive Task Analysis (CTA) tool: Goal Directed Information Analysis (GDIA), which was developed specifically for this study. Initially appropriate scenarios were developed. Based on the scenarios, 44 semi-structured interviews were carried out in three different elicitation phases with both novice and experienced fire fighters. Together with field observations of fire simulation and training exercises, fire and rescue related documentation; a comprehensive set of information needs of fire fighters was identified. These were validated through two different stages via 34 brainstorming sessions with the participation of a number of subject-matter experts. To explore appropriate presentation methods of information, software mock-up was developed. This mock-up is made up of several human computer interfaces, which were evaluated via 19 walkthrough and workshop sessions, involving 22 potential end-users and 14 other related experts. As a result, many of the methods used in the mock-up were confirmed as useful and appropriate and several refinements proposed. The outcomes of this study include: 1) A set of GDI Diagrams showing goal related information needs for each of the job roles with the link to their decision-making needs, 2) A series of practical recommendations suitable for designing of human computer interfaces of fire emergency response information system, 3) Human computer interface mock-ups for an information system to enhance Situation Awareness of fire fighters and 4) A conceptual architecture for the underlying information system. In addition, this study also developed an enhanced cognitive task analysis tool capable of exploring the needs of emergency first responders. This thesis contributes to our understanding of how information systems could be designed to enhance the Situation Awareness of first responders in a fire emergency. These results will be of particular interest to practicing information systems designers and developers in the FRS in the UK and to the wider academic community