Multilayer optimization in radio resource allocation for the packet transmission in wireless networks

In the last decade mobile wireless communications have witnessed an explosive growth in the user’s penetration rate and their widespread deployment around the globe. It is expected that this tendency will continue to increase with the convergence of fixed Internet wired networks with mobile ones and with the evolution to the full IP architecture paradigm. Therefore mobile wireless communications will be of paramount importance on the development of the information society of the near future. In particular a research topic of particular relevance in telecommunications nowadays is related to the design and implementation of mobile communication systems of 4th generation. 4G networks will be characterized by the support of multiple radio access technologies in a core network fully compliant with the Internet Protocol (all IP paradigm). Such networks will sustain the stringent quality of service (QoS) requirements and the expected high data rates from the type of multimedia applications to be available in the near future. The approach followed in the design and implementation of the mobile wireless networks of current generation (2G and 3G) has been the stratification of the architecture into a communication protocol model composed by a set of layers, in which each one encompasses some set of functionalities. In such protocol layered model, communications is only allowed between adjacent layers and through specific interface service points. This modular concept eases the implementation of new functionalities as the behaviour of each layer in the protocol stack is not affected by the others. However, the fact that lower layers in the protocol stack model do not utilize information available from upper layers, and vice versa, downgrades the performance achieved. This is particularly relevant if multiple antenna systems, in a MIMO (Multiple Input Multiple Output) configuration, are implemented. MIMO schemes introduce another degree of freedom for radio resource allocation: the space domain. Contrary to the time and frequency domains, radio resources mapped into the spatial domain cannot be assumed as completely orthogonal, due to the amount of interference resulting from users transmitting in the same frequency sub-channel and/or time slots but in different spatial beams. Therefore, the availability of information regarding the state of radio resources, from lower to upper layers, is of fundamental importance in the prosecution of the levels of QoS expected from those multimedia applications. In order to match applications requirements and the constraints of the mobile radio channel, in the last few years researches have proposed a new paradigm for the layered architecture for communications: the cross-layer design framework. In a general way, the cross-layer design paradigm refers to a protocol design in which the dependence between protocol layers is actively exploited, by breaking out the stringent rules which restrict the communication only between adjacent layers in the original reference model, and allowing direct interaction among different layers of the stack. An efficient management of the set of available radio resources demand for the implementation of efficient and low complexity packet schedulers which prioritize user’s transmissions according to inputs provided from lower as well as upper layers in the protocol stack, fully compliant with the cross-layer design paradigm. Specifically, efficiently designed packet schedulers for 4G networks should result in the maximization of the capacity available, through the consideration of the limitations imposed by the mobile radio channel and comply with the set of QoS requirements from the application layer. IEEE 802.16e standard, also named as Mobile WiMAX, seems to comply with the specifications of 4G mobile networks. The scalable architecture, low cost implementation and high data throughput, enable efficient data multiplexing and low data latency, which are attributes essential to enable broadband data services. Also, the connection oriented approach of Its medium access layer is fully compliant with the quality of service demands from such applications. Therefore, Mobile WiMAX seems to be a promising 4G mobile wireless networks candidate. In this thesis it is proposed the investigation, design and implementation of packet scheduling algorithms for the efficient management of the set of available radio resources, in time, frequency and spatial domains of the Mobile WiMAX networks. The proposed algorithms combine input metrics from physical layer and QoS requirements from upper layers, according to the crosslayer design paradigm. Proposed schedulers are evaluated by means of system level simulations, conducted in a system level simulation platform implementing the physical and medium access control layers of the IEEE802.16e standard.

Avaliação de desempenho dos treinadores: práticas e implicações no contexto da gestão dos clubes desportivos

O estudo tem por objetivo descrever e compreender o processo de avaliação de desempenho dos treinadores de desporto. Especificamente, procura-se aferir se a definição dos objetivos de trabalho, o escalão etário dos atletas, o nível competitivo, a situação contratual e a atribuição de prémios se relacionam com o facto de os treinadores serem ou não avaliados. Pretende-se ainda verificar se existe uma diferenciação dos critérios de avaliação de desempenho em função do nível competitivo em que o treinador atua e do escalão etário dos atletas. A metodologia de investigação foi alicerçada nos paradigmas interpretativo e positivista. Primeiramente, entrevistaram-se os responsáveis pela avaliação de desempenho de nove clubes desportivos da Madeira. Posteriormente, aplicou-se um questionário anónimo a 223 treinadores, sendo que os dados obtidos foram tratados com recurso à análise fatorial, ao teste T-Student, ao teste do Qui-Quadrado e à ANOVA. Os resultados descritivos dos grupos mostram que a avaliação de desempenho é uma prática pouco estruturada e assumida no âmbito gestão dos clubes. Com efeito, apresenta falhas ao nível da definição de instrumentos/critérios de avaliação e do feedback de desempenho. Os resultados da análise inferencial mostram que a definição dos objetivos, a situação contratual dos treinadores e a atribuição de prémios estão positivamente relacionados com a valorização da avaliação de desempenho. Os resultados revelam ainda a inexistência de uma distinção entre os critérios de avaliação dos treinadores que trabalham com atletas de diferentes escalões, à exceção dos resultados desportivos que foram mais valorizados para os treinadores de seniores. É de salientar ainda que foi entre os treinadores de atletas de nível nacional/internacional que se verificou maior valorização de critérios relacionados com a competição, nomeadamente: os resultados desportivos, as competências de planeamento, de formação dos atletas, de liderança e de scouting. Finalmente, deste estudo emerge a necessidade de um ajustamento entre o contexto em que o treinador atua e os critérios de avaliação do desempenho e de novas linhas de investigação, a fim de analisar a influência da avaliação de desempenho na eficiência e eficácia do treinador.