Write a MATLAB program to Simulate(modulate) BPSK signals for the data {10000111} and demodulate it using MATLAB. Plot all waveforms. Obtain a bit error rate graph.

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Nikshith Shetty
Nikshith Shetty 2020-12-12
回答： Idin Motedayen-Aval 2024-11-18，17:16
% This is for the modulation and Demodulation of BPSK for the data [ 1 0 0 0 0 1 1 1]
% If you obtain the Bit error rate for the given data please post it in the comments
% ********************* BPSK modulation and de-modulation ****************%
clc;
clear all;
close all;
% ********************* Define transmitted signal *************************
x_inp = [1 0 0 0 0 1 1 1]; % Binary information as stream of bits (binary signal 0 or 1)
N = length(x_inp);
Tb = 0.0001; %Data rate = 1MHz i.e., bit period (second)
disp('Binary Input Information at Transmitter: ');
disp(x_inp);
% ********************* Represent input signal as digital signal ****
x_bit=[];
nb=100; % Digital signal per bit
for n=1:1:N
if x_inp(n)==1;
x_bitt=ones(1,nb);
else x_inp(n)==0;
x_bitt=zeros(1,nb);
end
x_bit=[x_bit x_bitt];
end
t1=Tb/nb:Tb/nb:nb*N*(Tb/nb); % time of the signal
f1 = figure(1);
set(f1,'color',[1 1 1]);
subplot(3,1,1);
plot(t1,x_bit,'lineWidth',2);grid on;
axis([ 0 Tb*N -0.5 1.5]);
ylabel('Amplitude(volt)');
xlabel(' Time(sec)');
title('Input signal as digital signal');
% ********************* Define BPSK Modulation ****************************
Ac=5; % Amplitude of carrier signal
mc=4; % fc>>fs fc=mc*fs fs=1/Tb
fc=mc*(1/Tb); % carrier frequency for bit 1
fi1=0; % carrier phase for bit 1
fi2=pi; % carrier phase for bit 0
t2=Tb/nb:Tb/nb:Tb;
t2L=length(t2);
x_mod=[];
for (i=1:1:N)
if (x_inp(i)==1)
x_mod0=Ac*cos(2*pi*fc*t2+fi1);%modulation signal with carrier signal 1
else
x_mod0=Ac*cos(2*pi*fc*t2+fi2);%modulation signal with carrier signal 2
end
x_mod=[x_mod x_mod0];
end
t3=Tb/nb:Tb/nb:Tb*N;
subplot(3,1,2);
plot(t3,x_mod);
xlabel('Time(sec)');
ylabel('Amplitude(volt)');
title('Signal of BPSK modulation ');
% ********************* Transmitted signal x ******************************
x=x_mod;
% ********************* Channel model h and w *****************************
h=1; % Fading
w=0; % Noise
% ********************* Received signal y *********************************
y=h.*x+w;
% ********************* Define BPSK Demodulation **************************
y_dem=[];
for n=t2L:t2L:length(y)
t=Tb/nb:Tb/nb:Tb;
c=cos(2*pi*fc*t); % carrier siignal
y_dem0=c.*y((n-(t2L-1)):n);
t4=Tb/nb:Tb/nb:Tb;
z=trapz(t4,y_dem0); % intregation
A_dem=round((2*z/Tb));
if(A_dem>Ac/2) % logic level = Ac/2
A=1;
else
A=0;
end
y_dem=[y_dem A];
end
x_out=y_dem; % output signal;
% *************** Represent output signal as digital signal ***************
xx_bit=[];
for n=1:length(x_out);
if x_out(n)==1;
xx_bitt=ones(1,nb);
else x_out(n)==0;
xx_bitt=zeros(1,nb);
end
xx_bit=[xx_bit xx_bitt];
end
t4=Tb/nb:Tb/nb:nb*length(x_out)*(Tb/nb);
subplot(3,1,3)
plot(t4,xx_bit,'LineWidth',2);grid on;
axis([ 0 Tb*length(x_out) -0.5 1.5]);
ylabel('Amplitude(volt)');
xlabel(' Time(sec)');
title('Output signal as digital signal');

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采纳的回答

Nikshith Shetty
Nikshith Shetty 2020-12-15
编辑：Nikshith Shetty 2020-12-15
% This is for the modulation and Demodulation of BPSK for the data [ 1 0 0 0 0 1 1 1]
% If you obtain the Bit error rate for the given data please post it in the comments
% ********************* BPSK modulation and de-modulation ****************%
clc;
clear all;
close all;
% ********************* Define transmitted signal *************************
x_inp = [1 0 0 0 0 1 1 1]; % Binary information as stream of bits (binary signal 0 or 1)
N = length(x_inp);
Tb = 0.0001; %Data rate = 1MHz i.e., bit period (second)
disp('Binary Input Information at Transmitter: ');
disp(x_inp);
% ********************* Represent input signal as digital signal ****
x_bit=[];
nb=100; % Digital signal per bit
for n=1:1:N
if x_inp(n)==1;
x_bitt=ones(1,nb);
else x_inp(n)==0;
x_bitt=zeros(1,nb);
end
x_bit=[x_bit x_bitt];
end
t1=Tb/nb:Tb/nb:nb*N*(Tb/nb); % time of the signal
f1 = figure(1);
set(f1,'color',[1 1 1]);
subplot(3,1,1);
plot(t1,x_bit,'lineWidth',2);grid on;
axis([ 0 Tb*N -0.5 1.5]);
ylabel('Amplitude(volt)');
xlabel(' Time(sec)');
title('Input signal as digital signal');
% ********************* Define BPSK Modulation ****************************
Ac=5; % Amplitude of carrier signal
mc=4; % fc>>fs fc=mc*fs fs=1/Tb
fc=mc*(1/Tb); % carrier frequency for bit 1
fi1=0; % carrier phase for bit 1
fi2=pi; % carrier phase for bit 0
t2=Tb/nb:Tb/nb:Tb;
t2L=length(t2);
x_mod=[];
for (i=1:1:N)
if (x_inp(i)==1)
x_mod0=Ac*cos(2*pi*fc*t2+fi1);%modulation signal with carrier signal 1
else
x_mod0=Ac*cos(2*pi*fc*t2+fi2);%modulation signal with carrier signal 2
end
x_mod=[x_mod x_mod0];
end
t3=Tb/nb:Tb/nb:Tb*N;
subplot(3,1,2);
plot(t3,x_mod);
xlabel('Time(sec)');
ylabel('Amplitude(volt)');
title('Signal of BPSK modulation ');
% ********************* Transmitted signal x ******************************
x=x_mod;
% ********************* Channel model h and w *****************************
h=1; % Fading
w=0; % Noise
% ********************* Received signal y *********************************
y=h.*x+w;
% ********************* Define BPSK Demodulation **************************
y_dem=[];
for n=t2L:t2L:length(y)
t=Tb/nb:Tb/nb:Tb;
c=cos(2*pi*fc*t); % carrier siignal
y_dem0=c.*y((n-(t2L-1)):n);
t4=Tb/nb:Tb/nb:Tb;
z=trapz(t4,y_dem0); % intregation
A_dem=round((2*z/Tb));
if(A_dem>Ac/2) % logic level = Ac/2
A=1;
else
A=0;
end
y_dem=[y_dem A];
end
x_out=y_dem; % output signal;
% *************** Represent output signal as digital signal ***************
xx_bit=[];
for n=1:length(x_out);
if x_out(n)==1;
xx_bitt=ones(1,nb);
else x_out(n)==0;
xx_bitt=zeros(1,nb);
end
xx_bit=[xx_bit xx_bitt];
end
t4=Tb/nb:Tb/nb:nb*length(x_out)*(Tb/nb);
subplot(3,1,3)
plot(t4,xx_bit,'LineWidth',2);grid on;
axis([ 0 Tb*length(x_out) -0.5 1.5]);
ylabel('Amplitude(volt)');
xlabel(' Time(sec)');
title('Output signal as digital signal');

更多回答（1 个）

Idin Motedayen-Aval
Idin Motedayen-Aval 2024-11-18，17:16
The question, as stated, doesn't seem to be specific enough.
The given code plots 100 points for each bit of data, and shows the BPSK modulation on a carrier signal. That all seems to be fine.
Bit since this page is getting a fair number of views, it seems BPSK mod/demod is a popular topic. I am going to give some answers to the question in the title (ignoring the MATLAB code given above).
Modulating/demodulating a BPSK signal using Communications Toolbox is almost trivial:
x = [1 0 0 0 0 1 1 1]; % data
x_mod = pskmod(x,2); % BPSK Modulation
x_hat = pskdemod(x_mod,2); % BPSK Demodulation
% Plots (use "stairs" to give the stair-step shape)
subplot(3,1,1)
stairs(x)
subplot(3,1,2)
stairs(real(mod_x))
subplot(3,1,3)
stairs(x_hat)
To generate a bit error rate (BER) graph (as the last part of the title says), it is not enough to simulate 8 bits! One must simulate many more bits. Below is a very simple version of such a code (there are many more elaborate examples given in MATLAB Answers).
% To get bit error rate curve
% one needs many more bits (generated at random)
N = 1e6; % number of bits to simulate
x = randi([0,1],[N,1]); % generate N bits (1 million in this case)
x_mod = pskmod(x,2); % BPSK modulate
snr_vec = 0:9;
ber = zeros(size(snr_vec)); % pre-allocate BER vector
for idx = 1:length(snr_vec)
y = awgn(x_mod,snr_vec(idx)); % Add noise
x_hat = pskdemod(y,2); % demod received signal
errs = sum(x_hat~=x); % count errors
ber(idx) = errs/N;
end
figure % create new figure window
semilogy(snr_vec,ber,'-*')
Hope this helps someone.

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