1. Institute of Electrical Engineering, Slovak Academy of Sciences, Dúbravská cesta 9, Bratislava 841 04, Slovakia
2. Institute of Technological Sciences, Wuhan University, Wuhan 430072, China
3. Faculty of Electrical Engineering and Information Technology, Institute of Electronics and Photonics, Slovak University of Technology, Ilkovičova 3, Bratislava 812 19, Slovakia