1. School of Electrical and Automation Engineering, East China Jiaotong University, Nanchang 330013, P. R. China
2. Laboratory of Condensed Matter, Electronics and Signal Processing, Department of Physics, University of Dschang, P. O. Box 067, Dschang, Cameroon
3. School of Artificial Intelligence, Nanjing University of Information Science and Technology, Nanjing 210044, P. R. China
4. School of Physics and Electronics, Central South University, Changsha 410083, P. R. China