1. a Graduate Institute of Communication Engineering , Tatung University , 40, Chungshan N. Rd., 3rd Sec., Taipei, 104, Taiwan, R.O.C. Phone: Fax: E-mail:
2. b Department of Computer and Communication Engineering , China University of Technology , Taipei, 116, Taiwan, R.O.C.
3. c Graduate Institute of Communication Engineering , Tatung University , 40, Chungshan N. Rd., 3rd Sec., Taipei, 104, Taiwan, R.O.C.