1. Institute of Electrical Control Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
2. Institute of Communications Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan
3. Department of Electrical Engineering, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
4. National Mobile Communications Research Laboratory, Southeast University, Nanjing, China
5. School of Electrical and Electronics Engineering, Nanyang Technological University, Jurong West, Singapore