1. College of Engineering, Temple University, Philadelphia, PA 19122, USA.
2. Department of Electrical and Computer Engineering at North Carolina State University, Raleigh, NC, 27695 USA.
3. College of Engineering, Temple University, Philadelphia, PA 19122, USA. (e-mail: xiaonan.lu@ieee.org)
4. Department of Electrical Engineering at Southern Methodist University, Dallas, TX, 75275 USA.