1. Technical University of Sofia, Plovdiv Branch,Department of Electrical Engineering,Plovdiv,Bulgaria
2. The University of Plovdiv “Paisii Hilendarski”,Faculty of Physics and Technology,Department of Electricity and Telecommunications,Smolyan,Bulgaria
3. The University of Plovdiv “Paisii Hilendarski,”,Faculty of Physics and Technology,Department of Electronics, Telecommunications and Information Technologies,Plovdiv,Bulgaria