Identification of dialed telephone numbers in touch tone telephone system based on frequency analysis

This work investigates identification of dialed numbers in a touch-tone telephone system based on Dual Tone Multi Frequency (DTMF) signaling technique. The tone of each dialed number is a sum of two carrier frequencies uniquely assigned to the number and any dialed number can be uniquely identified or decoded by analyzing and locating the pair of frequencies where there is maximum energy or amplitude in the spectrum of each tone. Frequency analysis is performed using Discrete Time Fourier Transform (DTFT) and simulation steps and results of the decoding technique are presented. Reliable DTMF decoding is essential as nowadays the use of DTMF signaling is prevalent not only for ordinary telephone signaling but also remote controlling of home, industrial and rural applications.