[1] Univ Seville, Dept Elect Engn, Seville 41092, Spain
[2] Univ Politehn Bucuresti, Dept Comp Sci, Bucharest 060042, Romania
[3] Univ Cadiz, Sch Engn, Cadiz 11519, Spain
[4] Univ Munster, Inst Comp Sci, Commun & Networked Syst ComSys, D-48149 Munster, Germany