[1] Huawei Technol, France Res Ctr, F-92100 Paris, France
[2] Trinity Coll Dublin, Sch Comp Sci & Stat, Dublin 2, Ireland
[3] Shanghai Jiao Tong Univ, Dept Elect Engn, Shanghai 200240, Peoples R China
[4] Univ Massachusetts, Sch Comp Sci, Amherst, MA 01002 USA
[5] Tech Univ Berlin, Dept Elect Engn & Comp Sci, D-10623 Berlin, Germany