1. Department of Electrical Eng., National Taiwan Ocean University, Keelung, Taiwan 202, Republic of China
2. Department of Computer Science and Information Engineering, Fortune Institute of Technology, Chi-shan Town, Kaohsiung, Taiwan 842, Republic of China
3. College of Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801
4. Global Analytical Research & Development, Abbott Laboratories, 1401 Sheridan Road, North Chicago, Illinois 60064-6292