1. Universidade Federal do Rio de Janeiro, P.O. Box 68504,SMT - Signals, Multimedia, and Telecommunications Lab. DEL/Poli & PEE/COPPE/UFRJ,Rio de Janeiro,RJ,Brazil,21941-972
2. Engineering School, UFF, R. Passo da Patria, 156, room E-406,Niteroi,RJ,Brazil,24210-240