In wireless sensor networks (WS N), Network lifetime is a critical metric, therefore, maximizing the network lifetime is a key challenge. In this article, we study the problem of optimal power allocation, taking into account the estimation of total signal-to-noise ratio (S NR) at the Fusion Center (FC). In order to analyze the proposed approach, we start by applying it in to orthogonal channels, and then we extend it to non-orthogonal channels. We consider that nodes transmit their data over quasi-static Rayleigh fading channels (QS RC) where these nodes have channel state Information (CS I). S imulations that have been conducted using these different channel conditions show the efficiency of the proposed approach.