1. Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut, Einsteinufer 37, D-10587 Berlin, Germany, phone: +49 30 31002 503, e-mail: bach@hhi.fhg.de
2. Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institut, Einsteinufer 37, D-10587 Berlin, Germany, phone: +49 30 31002 503