1. University of Yaounde I,Dept. Electrical and Telecommunications Engineering,Yaounde,Cameroon
2. University of Ebolowa,Dept Electrical and Power Engineering,Ebolowa,Cameroon
3. CRIStAL Laboratory, CNRS-UMR,Villeneuve d'Ascq,France,59655
4. University of Yaounde I,Dept. Physic's,Yaounde,Cameroon