1. Jiangsu Key Laboratory of Wireless CommunicationsNanjing University of Posts and TelecommunicationsNanjingPeople's Republic of China
2. Department of Computer ScienceSan Diego State UniversitySan DiegoUSA
3. National Mobile Communications Research LaboratorySoutheast UniversityNanjingPeople's Republic of China
4. Communication Research CenterHarbin Institute of TechnologyHarbinPeople's Republic of China