Abstract: The detection of modulated signals and analysis has been verified under white Gaussian noise channel for different signal to noise ratiolevels.The up gradations of detection performance and reliability have been enhanced under white Gaussian noise channel using spectrum analysis method. In this paper we have developed different models and performed simulation using Mat lab version 2014a by spectrum analysis method for several digital modulated mobile signals commonly used in today’s communication world. The proposed spectrum method is based on modified Periodogarm algorithm is superior in simplicity of computation to detect the presence of mobile modulated signals efficiently at low SNR which can be used to sense spectrum effectively to solve the problem of spectrum scarcity.