In the second part of this assignment, we are interested in simulating amplitude
ID: 2082986 • Letter: I
Question
In the second part of this assignment, we are interested in simulating amplitude and angle modulations. More specifically, we would like to perform modulation and demodulation of a specific signal using DSB-SC modulation, AM, SSB modulation, FM and PM. To start, consider the signal g(t) = 2 Delta(t + 0.02/0.02) - 3 Delta(t - 0.02/0.02). 1) Based on the bandwidth of this signal, peak a suitable sampling rate and plot the discrete version of this signal in time and frequency domain with proper scaling. Justify the selection of sampling frequency. Calculate the energy of the signal in time and frequency domains using MATLAB. 2) Next perform DSB-SC modulation with carrier frequency 300Hz. Plot the modulated signal in time and frequency domain with proper scaling. What is the bandwidth of the modulated signal? Perform coherent demodulation twice with two different low-pass filters (LPFs): one with order 5 and the other with order 40. Plot the resulted (demodulated) signals in time and frequency domain with proper scaling. What is the difference between the two resulted demodulated signals? Explain. 3) Now we want to generate a DSB+C modulated signal. What is a proper selection for the carrier amplitude? Based on that calculate the modulation index. Plot the modulated signal in time and frequency domain with proper scaling. Using MATLAB, calculate the power efficiency in this case. Perform coherent demodulation using an LPF of order 40 and plot the resulted (demodulated) signal in time and frequency domain with proper scaling. If we are supposed to do non-coherent demodulation, sketch the demodulator circuit. What would be a good choice for R and C values in the envelope detector circuit?Explanation / Answer
clc; close all; clear all; disp(' example: m=1 means 100% modulation'); %m=input(' Enter the value of modulation index (m) = '); m=1; % for 100% modulation if (0>m||m>1) error('m may be less than or equal to one and geter than to zero'); end Am=5; % Amplitude of modulating signal fa=2000; % Frequency of modulating signal Ta=1/fa; % Time period of modulating signal t=0:Ta/999:6*Ta; % Total time for simulation ym=Am*sin(2*pi*fa*t); % Eqation of modulating signal figure(1) subplot(3,1,1); plot(t,ym), grid on;% Graphical representation of Modulating signal title ( ' Modulating Signal '); xlabel ( ' time(sec) '); ylabel (' Amplitud(volt) '); Ac=Am/m;% Amplitude of carrier signal [ where, modulation Index (m)=Am/Ac ] fc=fa*10;% Frequency of carrier signal Tc=1/fc;% Time period of carrier signal yc=Ac*sin(2*pi*fc*t);% Eqation of carrier signal subplot(3,1,2); plot(t,yc), grid on;% Graphical representation of carrier signal title ( ' Carrier Signal '); xlabel ( ' time(sec) '); ylabel (' Amplitud(volt) '); y=Ac*(1+m*sin(2*pi*fa*t)).*sin(2*pi*fc*t); % Equation of Amplitude %modulated signal subplot(3,1,3); plot(t,y);% Graphical representation of AM signal title ( ' Amplitude Modulated signal '); xlabel ( ' time(sec) '); ylabel (' Amplitud(volt) '); grid on;