1. Department of Electrical Engineering, National Formosa University, Wunhua Road 64, Huwei 632, Taiwan
2. Information Processing Lab, Technology University of Dortmund, Otto-Hahn-Strase 4, 44221 Dortmund, Germany
3. Institute of Electrical Engineering, National Taipei University, University Road 151, San Shia District, New Taipei City 23741, Taiwan