Fs-mac: um sistema para flexibilização da subcamada mac em redes sem fio

Abstract

Current wireless networks are very dynamic and have a wide variety of applications with very different requirements. As a consequence, there are many communication standards that deal with the specific problems and characteristics of each network, such as high interference, time varying channels and mobility. Moreover, applications with diverse requirements usually coexist within the same network. Applications such as voice and video, for example, require low latency to ensure quality in the transmission, but tolerate reasonable error rates. On the other hand, data applications such as web and message services have low error tolerance, however low latency is not an essential requirement. This diversity raises the need for more flexible equipment as well as networks that adapt to the context of the network. In the MAC sublayer, one of the problems that still persist is that the protocols are not efficient in all scenarios. Protocols based on TDMA (Time Division Multiple Access), for example, have good throughput when the medium is congested. However, due to the overhead of control messages used to allocate the slots, they are not suitable when the medium is not congested. In contrast, protocols based on CSMA (Carrier sense multiple access) are suitable for sparse networks because they have low overhead, but their performance decreases due to frequent message collisions when the medium is congested. This master thesis addresses proposes to increase the flexibility on the medium access control. We propose an architecture called FS-MAC (Flexible System for Me- dium Access Control), which is based on the working structure of cognitive radio. It allows more than one protocol to be used on the network, activating each one in the situation where it is most efficient. In addition, the solution uses a Fuzzy system to make decisions and allows new MAC protocols to be added to the existing set without changing the entire sublayer. We implemented a prototype of the architecture using Software Defined Radios (SDR), a technology that allows the programming of wireless protocols and applications with a high degree of flexibility. The prototype was tested in a testbed where we varied the load and number of connected stations. Regarding throughput, the results showed that FS-MAC was able to recognize the best scenario for each protocol and to activate each one when it is most efficient. We also performed tests where we modified the optimization objective, prioritizing the minimization of the number of retransmissions. In both cases, FS-MAC showed similar performance to the most efficient protocol at any given time, having an overhead of around 2%. In addition to the presented results, this work generated as contributions the following publications: FS-MAC: Uma Plataforma para a Flexibilização da Subcamada MAC em Redes Sem Fio [Cordeiro et al., 2017], Experimental Wireless Networking Research using Software-Defined Radios [Souza et al., 2017] and Introdução a Rádios Definidos por Software com aplicações em GNU Radio [Silva et al., 2015];.