کمک برای پروژه شبیه سازی متلب در درس مخابرات

">   [COLOR=#231F20][FONT=Futura-Heavy][B]Envelope detection of suppressed carrier signals[/B]
[COLOR=#231F20][FONT= ]Write a MATLAB program that emulates the envelope detector of Fig. 4.5–6a to
[COLOR=#231F20][FONT= ]have it detect a 100 percent modulated AM signal and then a D SB signal. Show why
[COLOR=#231F20][FONT= ]it is not suitable for detection of DSB signals. Use a single-tone message and plot
[COLOR=#231F20][FONT= ]the message, modulated signal, and the envelope detector output.[/FONT][/COLOR][/FONT][/COLOR][/FONT][/COLOR][/FONT][/COLOR]
[/FONT][/COLOR]

%show how an envelope detector demodulates AM and DSB signals
%Clear and initialize varables 
clear
for t=1:2000
   j(t)=t;
   xc_am(t)=0; %AM signal
   xc_dsb(t)=0; %DSB signal
   v_am(t)=0; %Rectified AM signal
   v_dsb(t)=0; %Rectified DSB signal
   y_am(t)=0; %output of envelope detector
   y_dsb(t)=0; %output of envelope detector 
   hlpf(t)=0; %LPF for envelope  detector 
end
j
fc=10^6; %carrier frequency is 10^6 Hz
fm=10^5; %message frequency is 10^5 Hz
Ts=1/(2*fc); %sample period is 1/(2*10^6) seconds
Ac=1.5; %carrier amplitude is 1.5
%Generate a signal-tone message 
for t=1:2000
    m(t)=cos(2*pi*fm*t*Ts);
end
%Generate AM and DSB modulated signals
for t=1:2000
    xc_am(t)=Ac*(1+m(t))*cos(2*pi*fc*t*Ts);
    xc_dsb(t)=Ac*m(t)*cos(2*pi*fc*t*Ts);
end
%Generate impulse response function for fifth order Butterworth
for t=1:2000
    hlpf(t)=(250000*exp(-t))/131981 - (309*exp(-(809*t)/1000)*(cos((3*38391^(1/2)*t)/1000) - (1309*38391^(1/2)*sin((3*38391^(1/2)*t)/1000))/186327))/191 - (191*exp(-(309*t)/1000)*(cos((904519^(1/2)*t)/1000) + (809*904519^(1/2)*sin((904519^(1/2)*t)/1000))/250019))/691;
end
%Demodulate the AM and DSB signals using an envelope detector 
%Rectify AM and DSB signals
for t=1:2000 
    if xc_am(t)>=0
        v_am(t)=xc_am(t);
    end
    if xc_dsb(t)>=0
        v_dsb(t)=xc_dsb(t);
    end
end 
%Low pass filter rectified signals via convolving with LPF
y_am=conv(hlpf,v_am);
y_dsb=conv(hlpf,v_dsb);
%Remove DC offset from signals [this function as the blocking capacitor]
%calculate DC offset by determining average value of signal
dc_am=0;
dc_dsb=0;
for t=1:2000 
    dc_am=dc_am+y_am(t);
    dc_dsb=dc_dsb+y_dsb(t);
end
dc_am=dc_am/2000;
dc_dsb=dc_dsb/2000;
%subtract DC offset
for t=1:2000
    y_am(t)=y_am(t)-dc_am;
    y_dsb(t)=y_dsb(t)-dc_dsb;
end
%Scale the message amplitudes
y_am=5*y_am/max(y_am);
y_dsb=5*y_dsb/max(y_dsb);
m=2*m/max(m);
%plot the modulated demodulated signals and original message and include
%adding offsets of 20,15,10,5 and 0 to signal amplitudes to enable them to
%fit on a signal figure
plot(j(1:150),xc_dsb(1:150)+20,j(1:150),y_dsb(1:150)+15,j(1:150),xc_am(1:150)+10,j(1:150),y_am(1:150)+5,j(1:150),m(1:150))