1. Polytechnic School of Pernambuco (Poli), University of Pernambuco (UPE), Recife 50720-001, PE, Brazil
2. Department of Electronics and Systems (DES), Universidade Federal de Pernambuco (UFPE), Recife 50740-550, PE, Brazil
3. David R. Cheriton School of Computer Science, University of Waterloo, Waterloo, ON N2L 3G1, Canada