1. Department of Electrical Engineering and Information Technology, University of Naples Federico II, Naples, Italy
2. Department of Astronautical, Electrical and Energy Engineering, University of Rome La Sapienza, Rome, Italy
3. Instituto de Telecomunicacoes, Instituto Superior Tecnico, Universidade de Lisboa, Lisboa, Portugal
4. Department of Electrical Engineering, Tsinghua University, Beijing, China
5. Kinectrics Inc., Toronto, ON, Canada