1. Department of Electrical Engineering, Chonnam National University, 77 Yongbong-Ro, Buk-Gu, Gwangju 500-756, Korea
2. Department of Electronic Engineering, Sunchon National University, 255 Jungang-Ro, Sunchon, Jeonnam 540-950, Korea
3. Division of Electrical, Electronic and Computer Engineering, Chonnam National University, 50 Daehak-Ro, Yeosu, Jeonnam 550-749, Korea