1. College of Information and Communication Engineering, Sungkyunkwan University, 2066 Seobu-Ro, Jangan-Gu, Suwon, Gyeonggi-Do 16419, Republic of Korea
2. Mobile Access Research Division, Electronics and Telecommunications Research Institute, 138 Gajeongno, Yuseong-gu, Daejeon 34129, Republic of Korea