1. a Department of Computer Engineering , Chungju National University , Chungju, 380-702, Republic of Korea
2. b Department of Electronic Engineering , Semyung University , Jecheon, 390-711, Republic of Korea
3. c School of Electrical and Electronic Engineering, Chung-Ang University , Seoul, 156-756, Republic of Korea
4. d Department of Mechanical Engineering , University of California , Riverside, CA, 92507, USA