www.pudn.com > BPSKmodanddemod.zip > BPSKmodanddemod.m

%BPSK simulation using a carrier cosine wave with ISI 
clc; 
close all; 
clear all; 
%figure(1) 
n=160 
for i=1:n 
    data(i)= 2*round(rand)-1; 
end 
%create modulated BPSK signal 
%first expand the bit stream 
exdata=[]; 
for i=1:length(data) 
  for rep=1:5 
  exdata= [exdata data(i)]; 
  end 
end 
ts=.1; 
t=1:ts:80.9; 
carrier=cos(pi*t); 
%multiply expanded bitstream by cosine wave with carrier frequency 
%this is the BPSK that is to be transmitted over the channel 
bpsk=carrier.*exdata; 
%bpsk=[bpsk(length(bpsk)-1) bpsk(length(bpsk)) bpsk]; 
%plot(bpsk) 
% generating the noise 
% p=rand(1,800)*2*pi; 
p=rand*2*pi; 
snr=10; 
r=sqrt(-1*(1/snr*log(1 - rand))); 
% no = 5*(r.* exp(j*p)); 
no = (r.* exp(j*p));     
% value of alpha  
al=rand+j*rand; 
%al=1; 
% Spreading channel with the alpha as the variable 
for k=5:5:795 
    for l = 1:5 
    %al=round(rand)+j*round(rand) 
     rec(k+l)=bpsk(k+l)+al*bpsk(k-5+l); 
    end 
end 
rxdata=rec+ no ; 
%begin demodulation 
%first multiply recieved bitstream by cosine wave with carrier frequency 
%figure(2) 
uncarry=rxdata.*carrier; 
%plot(uncarry) 
%demodulate by integrating  
dec1=[]; 
for inc=1:5:length(uncarry)    
  dec=trapz(inc:inc+4,uncarry(inc:inc+4)); 
  dec1=[dec1 dec]; 
end 
%make decision with a threshold of zero 
demod=[]; 
for i=1:length(dec1) 
    if dec1(i)>0 
        demod=[demod 1]; 
    else 
        demod=[demod -1]; 
    end 
end 
%stem(demod) 
%calculate errors 
error=0; 
for i=1:length(demod) 
    if data(i)~=demod(i) 
        error=error+1; 
    end 
end 
error 
ber=error/n 
figure(3) 
title('Comparing the Bits at transmitter and receiver') 
stem(data) 
hold 
stem(demod,'rx')