1. Department of Computer Science and Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
2. Division of Electronics and Information Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, South Korea
3. Division of Electronic Engineering and Intelligent Robot Research Center, Chonbuk National University, Jeonju, Jeonbuk 561-756, South Korea
4. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA 94720, USA