www.pudn.com > bpskspread.rar > bpsk_spread.m

%*********************BINARY PHASE SHIFT KEYING ******************* 
% 
% Simulation of BPSK system in presence of Additive White Guassian Noise 
% and Rayleigh fading and Dopper shift and using SPREAD SPECTRUM TECH 
% 
%******************DIRECT SEQUENCE SPREAD SEQUENCE****************** 
 
f_data=1;          % DATA FREQUENCY 
f_chip=11;         % LENGTH OF CHIP SEQUENCE 
fc=220;            % RELATIVE CARRIER FREQUENCY 
fs=fc*3;           % SAMPLING FREQUENCY 
N=fs/f_chip;       % CODING RATE 
data_length=1000;   
M=2;               % BINARY LEVEL CODING 
 
matches=0; 
errors=0; 
count=1; 
 
SNRpbit=0; 
SNR=SNRpbit; 
rand('state',12345);    % INITIALISATION 'SEED' 
randn('state',54321); 
 
numplot=100; 
 
msg_unspread=randsrc(data_length,1,[0:M-1]); % GENERATION OF RANDOM DATA  
 
 
PN_sequence=randsrc(11,1,[0:1]);             % GENERATION OF PN SEQUENCE 
 
% GENERATION OF SPREADED MESSAGE 
j=1; 
for i = 1:data_length 
    for k = j:j+f_chip 
        msg_orig(k) = msg_unspread(i); 
    end; 
    msg_orig(j:(j+f_chip-1)) = xor(msg_orig(j:(j+f_chip-1))',PN_sequence(1:f_chip)); 
    j = f_chip*i+1;     
end; 
 
len_of_orig=length(msg_orig); 
 
 
% MODULATING THE SPREAD MESSAGE  
msg_tx=dmod(msg_orig,fc,f_chip,fs,'psk',M); 
len_of_tx=length(msg_tx); 
 
 
% % RAYLEIGH COEFFICIENTS 
% magT=abs(T); 
%  
% % ADDING RAYLEGH FADING COEFFICIENTS 
%    k=1; 
%    for i=1:len_of_tx 
%       msg_tx(1,i)=msg_tx(1,i)*10*magT(1,k); 
%       if(mod(i,k)) 
%          k=k+300; 
%       end ; 
%    end;     
 
% PERFORMANCE ANALYSIS FOR VARYING SNR'S 
 
for SNRpbit=0:1:7 
   
    SNR=SNRpbit; 
    rand('state',12345); 
    randn('state',54321); 
 
   % ADDING AWGN TO THE SIGNAL  
    msg_rx_data=awgn(msg_tx,SNR-10*log10(N),'measured','dB');  
     
    % plot(t,msg_rx(1:length(t)),'b-'); 
    msg_rx= msg_rx_data ; 
        
   % DEMODULATING THE RECEIVED SIGNAL 
    msg_demod=ddemod(msg_rx,fc,f_chip,fs,'psk',M); 
 
   % CORRELATING WITH THE PN SEQUENCE  
    j=1; 
    for i = 1:data_length 
      msg_demod(j:(j+f_chip-1)) = xor(msg_demod(j:(j+f_chip-1))',PN_sequence(1:f_chip)); 
      j = f_chip*i+1;     
    end; 
 
   % DESPREADING THE RECEIVED SIGNAL 
    j=1; 
    for i = 1:data_length 
      sum=0; 
      for k = j:j+f_chip 
        sum=sum+msg_demod(k); 
      end; 
      if (sum >=7) 
        msg_demod_rec(i)=1; 
      else 
        msg_demod_rec(i)=0; 
      end;     
    j = f_chip*i+1;     
    end; 
  
   % CALCULATION OF ERRORS 
  
   for i=1:data_length; 
     if (msg_demod_rec(1,i)== msg_unspread(i,1)) 
           matches=matches+1; 
     else 
           errors=errors+1; 
     end ; 
   end;      
  
  % BER_ray(count)=errors/data_length; 
  BER_awgn(count)=errors/data_length; 
  %BER_theo(count)=0.07*erfc(SNR^0.5); 
    count=count+1; 
    errors=0; 
     
end;