新建 文本文档 (6).txt

利用MATLAB对扩频信号进行检测和参数估计

function cdmamodem(user1,user2,snr_in_dbs) 
% >>>multiple access b/w 2 users using DS CDMA 
% >>>format is : cdmamodem(user1,user2,snr_in_dbs) 
% >>>user1 and user2 are vectors and they should be of equal length 
% >>>e.g. user1=[1 0 1 0 1 0 1] , user2=[1 1 0 0 0 1 1],snr_in_dbs=-50 
% >>>or snr_in_dbs=50 just any number wud do 
%        Waqas Mansoor 
%         NUST , Pakistan 
 
close all 
%user1=[1 0 0 1 1 0] 
%user2=[1 1 0 1 0 0] 
%% to convert the binary sequences to bipolar NRZ format 
length_user1=length(user1); 
length_user2=length(user2); 
 
for i=1:length_user1 
    if user1(i)==0 
        user1(i)=-1; 
    end 
end 
 
for i=1:length_user2 
    if user2(i)==0 
        user2(i)=-1; 
    end 
end 
 
fc=1; %%carrier frequency 
eb=2;     %% energy per bit 
tb=1; %% time per bit of message sequence 
 
%%% CDMA transmitter for user1 
t=0.01:0.01:tb*length_user1; %0.01 
%%plotting base band signal for user1 
basebandsig1=[]; 
for i=1:length_user1 
    for j=0.01:0.01:tb%0.01 
          if user1(i)==1  
              basebandsig1=[basebandsig1 1]; 
          else  
              basebandsig1=[basebandsig1 -1]; 
          end 
    end 
end 
 
figure 
plot(basebandsig1) 
axis([0 100*length_user1 -1.5 1.5]); 
title('original binary sequence for user1 is') 
 
%%%% BPSK MODULATION FOR USER 1 
bpskmod1=[]; 
for i=1:length_user1 
    for j=0.01:0.01:tb 
     bpskmod1=[bpskmod1 sqrt(2*eb)*user1(i)*cos(2*pi*fc*j)]; 
 end 
end 
length(bpskmod1) 
 figure 
 plot(bpskmod1) 
%axis([0 100*length_user1 -2 2]); 
 title(' BPSK signal for user 1 is') 
 
%% plot fft of BPSK sequence 
% figure 
% plot(real(fft(bpskmod1))) 
% title('FFT of BPSK signal for user1 is') 
 
%% PN generator for user1 
%% let initial seed for user1 is 1000 
seed1=[1 -1 1 -1];  %convert it into bipolar NRZ format  
spreadspectrum1=[]; 
pn1=[]; 
 
for i=1:length_user1 
    for j=1:10 %chip rate is 10 times the bit rate 
        pn1=[pn1 seed1(4)];   
        if seed1 (4)==seed1(3) temp=-1; 
          else temp=1; 
          end 
              seed1(4)=seed1(3); 
              seed1(3)=seed1(2); 
              seed1(2)=seed1(1); 
              seed1(1)=temp; 
    end 
%         spreadspectrum1=[spreadspectrum1 user1(i)*pn1]; 
end 
 
% each bit has 100 samples. and each pn chip has 10 samples. there r  
% 10 chip per bit there fore size of pn samples and original bit is same 
 
pnupsampled1=[]; 
len_pn1=length(pn1); 
for i=1:len_pn1 
    for j=0.1:0.1:tb 
          if pn1(i)==1  
              pnupsampled1=[pnupsampled1 1]; 
          else  
              pnupsampled1=[pnupsampled1 -1]; 
          end 
    end 
end 
length_pnupsampled1=length(pnupsampled1); 
 sigtx1=bpskmod1.*pnupsampled1; 
  
figure 
plot(sigtx1) 
%axis([0 100*length_user1 -2 2]); 
title(' spread spectrum signal transmitted for user 1 is') 
 
%% plot fft of BPSK sequence 
figure 
plot(real(fft(sigtx1))) 
title('FFT of spread spectrum signal transmitted for user1 is') 
 
% rxcode1=pnupsampled1.*sigtx1; 
% figure 
% plot(rxcode1) 
% %axis([0 100*length_user1 -2 2]); 
% title(' spread spectrum signal transmitted for user 1 is') 
 
 
%%% CDMA transmitter for user2 
t=0.01:0.01:tb*length_user2; %0.01 
%%plotting base band signal for user2 
basebandsig2=[]; 
for i=1:length_user2 
    for j=0.01:0.01:tb%0.01 
          if user2(i)==1  
              basebandsig2=[basebandsig2 1]; 
          else  
              basebandsig2=[basebandsig2 -1]; 
          end 
    end 
end 
 
figure 
plot(basebandsig2) 
axis([0 100*length_user2 -1.5 1.5]); 
title('original binary sequence for user2 is') 
 
%%%% BPSK MODULATION FOR USER 2 
bpskmod2=[]; 
for i=1:length_user2 
    for j=0.01:0.01:tb 
     bpskmod2=[bpskmod2 sqrt(2*eb)*user2(i)*cos(2*pi*fc*j)]; 
 end 
end 
 figure 
 plot(bpskmod2) 
%axis([0 100*length_user2 -2 2]); 
 title(' BPSK signal for user 2 is') 
 
%% plot fft of BPSK sequence 
% figure 
% plot(real(fft(bpskmod2))) 
% title('FFT of BPSK signal for user2 is') 
 
%% PN generator for user2 
%% let initial seed for user2 is 1000 
seed2=[-1 1 -1 1];  %convert it into bipolar NRZ format  
spreadspectrum2=[]; 
pn2=[]; 
 
for i=1:length_user2 
    for j=1:10 %chip rate is 10 times the bit rate 
        pn2=[pn2 seed2(4)];   
        if seed2 (4)==seed2(3) temp=-1; 
          else temp=1; 
          end 
              seed2(4)=seed2(3); 
              seed2(3)=seed2(2); 
              seed2(2)=seed2(1); 
              seed2(1)=temp; 
    end 
%         spreadspectrum2=[spreadspectrum2 user2(i)*pn2]; 
end 
pnupsampled2=[]; 
len_pn2=length(pn2); 
for i=1:len_pn2 
    for j=0.1:0.1:tb 
          if pn2(i)==1  
              pnupsampled2=[pnupsampled2 1]; 
          else  
              pnupsampled2=[pnupsampled2 -1]; 
          end 
    end 
end 
length_pnupsampled2=length(pnupsampled2); 
 sigtx2=bpskmod2.*pnupsampled2; 
  
figure 
plot(sigtx2) 
%axis([0 100*length_user2 -2 2]); 
title(' spread spectrum signal transmitted for user 2 is') 
 
%% plot fft of BPSK sequence 
figure 
plot(real(fft(sigtx2))) 
title('FFT of spread spectrum signal transmitted for user2 is') 
 
% rxcode2=pnupsampled2.*sigtx2; 
% figure 
% plot(rxcode2) 
% %axis([0 100*length_user2 -2 2]); 
% title(' spread spectrum signal transmitted for user 2 is') 
 
%%%%%%%%%%%%%%%signal by adding the above 2 signals%%%%%%%%%%% 
composite_signal=sigtx1+sigtx2; 
 
%%%%%%%%%%%%%AWGN CHANNEL%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
composite_signal=awgn(composite_signal,snr_in_dbs);  %% SNR of % dbs 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 
 
%%%%%%%%%%%%%DMODULATION FOR USER 1%%%%%%%%%%%%%%%%%%%% 
rx1=composite_signal.*pnupsampled1; 
figure 
plot(rx1) 
 
%%%% BPSK DEMODULATION FOR USER 1 
demodcar1=[]; 
for i=1:length_user1 
    for j=0.01:0.01:tb 
     demodcar1=[demodcar1 sqrt(2*eb)*cos(2*pi*fc*j)]; 
 end 
end 
bpskdemod1=rx1.*demodcar1; 
figure 
plot(bpskdemod1) 
title('o/p of bpsk demod for user 1 is ') 
len_dmod1=length(bpskdemod1); 
sum=zeros(1,len_dmod1/100); 
for i=1:len_dmod1/100 
    for j=(i-1)*100+1:i*100 
        sum(i)=sum(i)+bpskdemod1(j); 
    end 
end 
sum; 
   
 rxbits1=[]; 
 for i=1:length_user1 
    if sum(i)>0 
        rxbits1=[rxbits1 1]; 
    else 
        rxbits1=[rxbits1 0]; 
    end 
 end 
rxbits1 
 
%%%%%%%%%%%%%DMODULATION FOR USER 2%%%%%%%%%%%%%%%%%%%% 
rx2=composite_signal.*pnupsampled2; 
figure 
plot(rx2) 
 
%%%% BPSK DEMODULATION FOR USER 2 
demodcar2=[]; 
for i=1:length_user2 
    for j=0.01:0.01:tb 
     demodcar2=[demodcar2 sqrt(2*eb)*cos(2*pi*fc*j)]; 
 end 
end 
bpskdemod2=rx2.*demodcar2; 
figure 
plot(bpskdemod2) 
title('o/p of bpsk demod for user 2 is ') 
len_dmod2=length(bpskdemod2); 
sum=zeros(1,len_dmod1/100); 
for i=1:len_dmod2/100 
    for j=(i-1)*100+1:i*100 
        sum(i)=sum(i)+bpskdemod2(j); 
    end 
end 
sum; 
   
 rxbits2=[]; 
 for i=1:length_user2 
    if sum(i)>0 
        rxbits2=[rxbits2 1]; 
    else 
        rxbits2=[rxbits2 0]; 
    end 
 end 
rxbits2