Simulating DC Offset Impairment in MATLAB

This document explains how to simulate DC offset impairment and its effect on constellation diagrams using MATLAB code. The code is structured into parts, with parts A and C being identical to the code used on the AWGN page (presumably a related resource). This section focuses on the MATLAB code responsible for simulating the DC offset.

Part B: DC Offset Simulation

DCO=input('Enter DC offset:(default:2.5)');
%map_out_dc= (real(mapper_out)+DCO) +i*(imag(mapper_out)+DCO);
map_out_dc= mapper_out* DCO;

%figure;plot(real(mapper_out_ori),imag(mapper_out_ori),'b+');title('constellation without DC offset');
figure;plot(real(map_out_dc),imag(map_out_dc),'r+');title('constellation with DC offset');

Explanation:

1. DCO=input('Enter DC offset:(default:2.5)'): This line prompts the user to enter the desired DC offset value. If no value is entered, the default value of 2.5 is used.

2. map_out_dc= mapper_out* DCO;: This line simulates the DC offset impairment. The original signal, represented by mapper_out, is multiplied by the DC offset value (DCO). Note: The commented-out line map_out_dc= (real(mapper_out)+DCO) +i_(imag(mapper_out)+DCO); represents an alternative, and potentially more accurate, way of applying the DC offset by adding it to the real and imaginary components separately.*

3. figure;plot(real(map_out_dc),imag(map_out_dc),'r+');title('constellation with DC offset');: This section generates a constellation diagram of the signal after the DC offset has been applied. The plot function displays the real and imaginary components of map_out_dc as red plus signs (‘r+’). The title command adds the title “constellation with DC offset” to the plot. The commented-out lines would have plotted the original signal.

Constellation Diagrams

Here are example constellation diagrams to illustrate the effect of DC offset.

Input constellation diagram (without DC offset)

Constellation diagram with DC offset

As you can see from the example images, DC offset shifts the entire constellation away from the origin. This shift can cause errors in demodulation if not properly compensated for.