[pt] Sistemas de Medição de Desempenho (SMD) são amplamente estudados por meio de trabalhos teóricos e práticos. No âmbito de trabalhos práticos, é identificado na literatura uma carência de estudos empíricos que englobem a etapa de implementação. Já os estudos que abordam tal etapa relatam diversas barreiras, o que corrobora com a necessidade de considerar a etapa piloto antes da implementação completa. Essa dissertação de mestrado tem como objetivo: propor um framework conceitual com diretrizes para o redesenho de SMD já existentes comtemplando formalmente uma etapa piloto e realizar o redesenho de um SMD através da utilização de um estudo empírico utilizando o framework conceitual proposto. Além redesenhar o processo e avaliar as barreiras enfrentadas em sua implantação, a dissertação fornece uma avaliação da forma com que a etapa piloto introduzida conseguiu mitigar os riscos mapeados na literatura. / [en] Performance Measurement Systems (PMS) are extensively studied through theoretical and practical work. In the scope of practical work, a lack of empirical studies concerning the implementation stage is identified in the literature. The studies that approach this stage report several barriers, which corroborates with the need to consider the pilot stage before full implementation. This dissertation aims to: propose a conceptual framework with guidelines for the redesign of existing PMS by formally contemplating a pilot phase and carry out the redesign of an PMS through the use of an empirical study using the proposed conceptual framework. In addition to redesigning the process and evaluating the barriers faced in its implementation, the dissertation provides an evaluation of the way in which the pilot stage introduced managed to mitigate the risks mapped in the literature.

Approved for public release; distribution is unlimited / OFDM systems have experienced increased attention in recent years and have found applications in a number of diverse areas including telephone-line based ADSL links, digital audio and video broadcasting systems, and wireless local area networks (WLAN). Orthogonal frequency-division multiplexing (OFDM) is a powerful technique for high data-rate transmission over fading channels. However, to deploy OFDM in a WLAN environment, precise frequency synchronization must be maintained and tricky frequency offsets must be handled. In this thesis, various techniques to improve the data throughput of OFDM WLAN are investigated. A simulation tool was developed in Matlab to evaluate the performance of the IEEE 802.11a physical layer. We proposed a rapid time and frequency synchronization algorithm using only the short training sequence of the IEEE 802.11a standard, thus reducing the training overhead to 50%. Particular attention was paid to channel coding, block interleaving and antenna diversity. Computer simulation showed that drastic improvement in error rate performance is achievable when these techniques are deployed. / Lieutenant, Hellenic Navy