1. a Graduate Institute of Communications Engineering, National Changhua University of Education, Changhua, Taiwan 500, R.O.C.
2. b Department of Electrical Engineering, Feng Chia University, Taichung, Taiwan 40724, R.O.C.
3. c Graduate Institute of Communications Engineering, Department of Electronics Engineering, National Changhua University of Education, Changhua, Taiwan 500, R.O.C.;, Email: iecher@cc.ncue.edu.tw