1. Electronic Engineering Department, University of Seville, Camino de los Descubrimientos S/N, 41092 Seville, Spain
2. School of Engineering, University of Cádiz, Avenida Universidad, No. 10, Puerto Real, 11519 Cadiz, Spain
3. Faculty of Automatic Control and Computers, University Politehnica of Bucharest, 313 Splaiul Independentei, 060042 Bucharest, Romania