1. a Department of Electrical Engineering, Pohang University of Science and Technology, Pohang, Gyungbuk 790-784, South Korea
2. b Department of Electrical Engineering, Pohang University of Science and Technology, Pohang, Gyungbuk 790-784, South Korea
3. c Samsung Electronics Co., Maetan-3 dong, Yeongtong-gu, Suwon-city, Gyeonggi 442-600, South Korea
4. d Department of Electrical Engineering, Pohang University of Science and Technology, Pohang, Gyungbuk 790-784, South Korea;, Email: syoh@postech.ac.kr