Todas as correções determinadas pelo júri, e só essas, foram efetuadas. O Presidente do Júri, Porto, ______/______/_________ I would like to thank my supervisor Prof. Miguel Coimbra for accepting to supervise my thesis, providing time and expertise and pushing me to new territories. It was a challenging experience, but very rewarding. I would like to thank Malik Sultan for his technical advice, general guidance and friendship during this entire process. None of this would be possible without my wife. Her support, patience through every step was instrumental to allow me to get to this point. She was also a great reviewer giving me nice pointers and suggestions. I'm also thankful for my family for providing me with moral support for my Master studies and my life in general. I would also like to thank the Instituto de Telecomunicações-IT for providing me with the dataset used in this thesis, allowing me to do the necessary research with it.