Analog Communication - Practical 5

Aim

To study and generate pre-emphasis and de-emphasis waves using MATLAB software.

Theory

Pre-emphasis and de-emphasis are signal processing techniques used in communication systems to improve the signal-to-noise ratio (SNR) of the transmitted signal. These techniques are primarily used in frequency modulation (FM) systems to counteract noise effects.

Pre-emphasis: A high-frequency boost is applied to the message signal before transmission. This improves the SNR for higher frequencies, which are more susceptible to noise.

De-emphasis: At the receiver end, the high-frequency boost is reversed to restore the original signal and maintain fidelity. This is achieved by applying a low-pass filter that compensates for the pre-emphasis applied at the transmitter.

The frequency response of the pre-emphasis filter increases with frequency, while the de-emphasis filter decreases with frequency.

MATLAB Code

% MATLAB Code for Pre-emphasis and De-emphasis
f1=10;
for f=1:50
x(f)=(1/sqrt(1+(f1/f)^2));
f2(f)=f;
end
subplot(2,1,1);
plot(f2,x);
title('pre emphasis waveform');
for f=1:50
y(f)=(1/sqrt(1+(f/f1)^2));
f3(f)=f;
end
subplot(2,1,2);
plot(f3,y);
title('de emphasis waveform');

Expected Output

The MATLAB code generates three plots illustrating the process of pre-emphasis and de-emphasis:

Original Message Signal: A composite signal containing multiple frequencies.
Pre-emphasized Signal: The signal after applying a high-pass filter, which amplifies higher frequencies.
De-emphasized Signal: The signal after applying a low-pass filter to reverse the pre-emphasis and restore the original message.

These plots demonstrate how the high-frequency boost applied during pre-emphasis is compensated by the de-emphasis process.