Beatriz Quinta, Ricardo A. M. Pereira, Institute of Telecommunications, University of Aveiro, Aveiro, 3810-193, Portugal, Portugal; Carolina Gouveia, Colab Almascience, Madan Parque, 2829-516 Caparica, Portugal, Portugal; Daniel Albuquerque, Escola Superior de Tecnologia e Gestao de ˜ Agueda, 3750-127 ´ Agueda, Portugal, Portugal; Pedro Pinho, Institute of Telecommunications, University of Aveiro, Aveiro, 3810-193, Portugal, Portugal