Department of Informatics Engineering, Department of Electrotechnical Engineering, ISEP, Rua Dr Bernardino Almeida 431, Porto, Portugal. acc@isep.ipp.pt|Department of Informatics Engineering, Department of Electrotechnical Engineering, ISEP, Rua Dr Bernardino Almeida 431, Porto, Portugal. acc@isep.ipp.pt|Department of Informatics Engineering, Department of Electrotechnical Engineering, ISEP, Rua Dr Bernardino Almeida 431, Porto, Portugal. acc@isep.ipp.pt