1. Inatel, Santa Rita do Sapucaí, Brazil
2. Department of Computer Engineering, Federal University of Ceará, Sobral, Brazil
3. School of Electrical and Information Engineering, University of the Witwatersrand, Johannesburg, South Africa
4. Wireless Technology Laboratory (WissTek), Department of Communications, School of Electrical and Computation Engineering, State University of Campinas, DECOM/FEEC/UNICAMP, Campinas, Brazil