Dual-tone multi-frequency (DTMF) signals are the tones (sinusoidal signals) generated by a telephone keypad. Each digit on the keypad is coded to a signal that is composed of two sinusoids, based on Table 1. Table 1: DTMF Tones 1336 Hz 1209 Hz 1477Hz 697 Hz 1 4 7 852 Hz 2 5 8 770 Hz 3 6 9 For instance, once the button for digit “1” is pressed, the signal sin(2π1336t) + sin(2π697t) is generated by the phone, where the signal duration is 0.5 seconds. At the decoder, each digit is identified based on the same pre-defined tone combination. One important application of DMTF is private branch exchange (PBX), which is a private telephone network used within an organization. In PBX systems, each telephone line connected to the PBX is assigned an extension number. Someone who dials the organization’s number, once connected, is asked to enter the desired extension number of a specific party. Based on the keyed extension number (input signal), the call is routed to the appropriate telephone line within the organization. The objective of this project is to design a DTMF decoder, which is capable of decoding a fourdigit extension number. Note that a four-digit extension number is composed of four consecutive DMTF tones based on Table 1. Twenty signals are uploaded to blackboard. Signals “TestSignal No1” to “TestSignal No10” are noiseless signals, while signal “TestSignal No11” to “TestSignal No20” are noisy signals. All signals are sampled with 8 kHz sampling frequency. Note: in MATLAB, you can sound any of the test signals using the “play” function. In this project, each group will design and implement a DTMF decoder in MATLAB/Simulink. The decoder should be able to decode any four-digit extension number generated from Table 1, whether noisy or noiseless. Thus, the input to the decoder should be any of the test signal (or any signal generated based on Table 1), and the output should be the corresponding four-digit extension number.
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