[1] Nanyang Technol Univ, Sch Phys & Math Sci, Singapore 637371, Singapore
[2] US Army DEVCOM Army Res Lab South, Houston, TX 77005 USA
[3] Rice Univ, Dept Elect & Comp Engn, Houston, TX 77005 USA
[4] Univ Sannio, Dept Engn, I-82100 Benevento, BN, Italy
[5] Univ Southern Calif, Ming Hsieh Dept Elect & Comp Engn, Los Angeles, CA 90089 USA