1. University Carlos III of Madrid,Signal Theory and Communication Department,Leganés,Spain
2. Universidad Politécnica de Madrid,ETSI de Telecomunicación,Departamento de Matemática Aplicada a las TIC,Madrid,Spain
3. University of Colorado Boulder,Department of Electrical, Computer, and Energy Engineering,Boulder,CO,USA
4. Scuola Superiore Meridionale,Napoli,Italy,80138