1. Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Avenue, Ann Arbor, MI 48109-2122, USA
2. Department of Electrical Engineering, Tatung Institute of Technology, 40 Chungshan N. Rd., 3rd Sec, Taipei, Taiwan
3. Department of Electrical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusong-dong, Yusong-gu Taejon 305-701, Korea