1. Key Laboratory of Dynamic Cognitive System of Electromagnetic Spectrum Space, Nanjing University of Aeronautics and Astronautics, Nanjing, P. R. China
2. No.8511 Research Institute of CASIC, Nanjing, P. R. China
3. School of Communication and Information Engineering, Xi'an University of Posts and Telecommunications, Xi'an, P. R. China
4. School of Electronics and Information, Northwestern Polytechnical University, P. R. China
5. Department of Informatics & Telecommunications, University of Thessaly, Lamia, Greece