The invention provides a method for generating signal envelope by demodulating received signals. The received signals comprise the characteristics of transmitting with a carrier frequency, modulating pulse series of data symbol with a given baud rate according to the preset communication protocol, and defining the modulated signals by the preset communication protocol. The method includes: measuring the duration of time of selected characteristics in the signal envelope defined by the communication protocol. Without pulse counting of the received signals, the baud rate of signals is estimatedbased on the measured duration of time. The signal envelope is processed in respond to the estimated baud rate so as to transcode the data symbol.