nadatelwazane / am-modulation

DSB-SC Modulation using MATLAB

Background

Double Sideband modulation is the easiest and most direct type of analog modulation. In this scheme, the modulated signal is obtained using a direct multiplication of the modulating signal (i.e. the message) by a cosine carrier. If the carrier term is omitted, the modulation is termed double sideband suppressed carrier (DSB-SC). DSB-TC has a significant advantage in the receiver design (i.e. the envelop detector). However, the DSB-TC loses to the other variant (i.e. the SC) in terms of power efficiency.

Procedure

• Use Matlab to read the attached audio file ("eric.wav") which has a sampling frequency Fs= 48 KHz, plot the spectrum of this signal.
• Use an ideal filter to remove all frequencies greater than 4KHZ.
• Obtain the filtered signal in both frequency and time domain.
• Sound the filtered audio signal (make sure that there is only a small error in the filtered signal)
• Generate DSB-SC modulated signal using a carrier signal with carrier frequency Fc=100 KHz, (Note : you have to increase the sampling frequency of filtered signal to be (Fs=5*Fc) before modulation process)
• Demodulate the modulated signal using a coherent detection receiver with SNR=0 ,10, 30 dB.
• For the three SNR cases; sound the received signal and plot it in both time and frequency domain, what conclusion you make of that? (Note: to sound signal after demodulation process you have to decrease the sampling frequency again).
• Repeat the coherent detection with frequency error, Fc=100.1 KHz instead of 100 KHz at receiver with SNR=10dB.
• Repeat the coherent detection with phase error=200 at receiver with SNR=10db.

Contributors

• Nada Alaa Mohamed
• Nada Elwazane