[1] Dept. of Electron. and Elec. Eng., University of Strathclyde, Glasgow G1 1XW, United Kingdom
[2] GMD-Fokus, Kaiserin-Augusta-Allee 31, Berlin, Germany
[3] Computer Science Department, Humboldt University, Berlin, Germany
[4] Dept. of Electron. and Elec. Eng., University of Strathclyde, Glasgow, United Kingdom
[5] University of Strathclyde, Glasgow, United Kingdom