1. Department of Electrical Engineering; Federal University of Para; Av. Augusto Corrêa, n 1, CEP 66075-900 Belém Pará Brazil
2. Technological Institute of Aeronautics; Praça Marechal Eduardo Gomes; 50-Vila das Acácias, CEP 12228-900 São José dos Campos São Paulo Brazil
3. Research and Development Center in Telecommunications (CPqD); Rod SP 340, Km 118,5-Fazenda Pau D'alho, CEP 13086-902 Campinas São Paulo Brazil