1. Key Laboratory of Underwater Acoustic Communication and Marine Information Technology of the Ministry of Education, Xiamen University, Xiamen, Fujian 361005, China
2. Department of Electrical and Computer Engineering, University of Alabama, Tuscaloosa, Alabama 35487, USA
3. Department of Computer Science and Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA