1. Department of Electrical and Computer Engineering, University of Houston, Houston, TX, USA
2. School of Electronics, Peking University, Beijing, China
3. Department of Engineering Technology, University of Houston, Houston, TX, USA
4. Center for Pervasive Communications and Computing, University of California at Irvine, Irvine, CA, USA
5. Department of Electrical and Computer Engineering, Princeton University, Princeton, NJ, USA