Global navigation satellite system “GNSS” is defined as a set of positioning satellite systems offering the possibility for a receiver to determine its position at any time and in any place on earth. The accuracy of this calculation, which is extremely solicited, is disputed by the phenomenon of multipath. for this purpose, several multipath mitigation techniques have been proposed in the literature. To prove the effectiveness of these methods, a preliminary assessment of their performances in the presence of multipath is more than necessary. This assessment is done by criteria such as the multipath error envelope and the running average of the multipath error envelope. In this project, we propose the derivation of mathematical models characterizing the average of the multipath error envelope of the C / A-GPS and BOC (n,n) Galileo signals for different values of the spacing between the delay locked loop correlators. The obtained results have shown that the pro-posed analytical models coincide with the numerical ones.