How can we separate mixed signals
Hi Nouali Ibrahim Yassine, 

Without any additional information about the two signals, what you are trying to do is a blind source separation. This means that you will have to use a set of advanced statistical tools ( principal components analysis or independent component analysis for example, I would go more for the Independant component analysis) to try to figure out different signal patterns. 

If you can have additional information about your signals (I guess you know your sensors, their number, their signal characteristics such as spectral distribution or some pre recorded patterns that you can use to correlate with the mixed signal, their inter-correlation) You may find a simpler solution to your problem. 

In any case, here is some lecture about the methods that I stated. There may be other ones that are better suited for your problem. 

Blind source seperation in general : 
https://perso.univ-rennes1.fr/laurent.albera/alberasiteweb/bss.html
Principal component analysis : 
http://www.sthda.com/english/articles/31-principal-component-methods-in-r-practical-guide/112-pca-principal-component-analysis-essentials/
Principal component analysis versus Independant component analysis : 
https://www.quora.com/What-is-the-difference-between-PCA-and-ICA

Best regards,

Mourad