Sang Uk Shin+ and Kyung Hyune Rhee++
+Electronics and Telecommunications Research Institute
Yusong-Gu, Daejon, 305-350, Korea
E-mail: shinsu@etri.re.kr
++Division of Electronics, Computer and Telecommunications Engineering
PuKyong National University
Nam-Gu, Pusan, 608-737, Korea
E-mail: khrhee@pknu.ac.kr