1. a Institut Fresnel, Faculte des Sciences de Saint-Jerome , Marseille cedex , France
2. b Ericsson AB, Ericsson Research, Wireless Access Networks , Kista , Sweden
3. c GREMAQ-University Toulouse I, Manufacture des Tabacs, Alle de Brienne , Toulouse , France
4. d School of Operations Research and Industrial Engineering, Cornell University , Ithaca , New York , USA
5. e Department of Mathematics , Chalmers University of Technology , Gothenburg , Sweden