[1] Politecn Torino, Dept Elect & Telecommun, Turin, Italy
[2] Univ Helsinki, Dept Comp Sci, Helsinki, Finland
[3] Univ Politecn Cartagena, Cartagena, Spain
[4] Univ Calif Irvine, Irvine, CA USA
[5] Natl Tech Univ Athens, Geodesy & Nav, Athens, Greece