iq_demod.m

The result is an IS-95CDMA forward link software simulation package ,which mimics real-time data com

function R_received =IQ_demod(combined,I_PN_state2,Q_PN_state2)


%IQ demodulator
%It carries out the in phase and quadrature phase demodulation of the received data signal the in phase Stream,which contains the real amplitude component of each signal element in the multipaht signal and Quadrature phase Stream.which contains the imaginary amplitude component of each signal element in the multipath signal I and Q pilot PN sequence generator are both 15 stage shift register

%assign the stage values of I pilot PN Sequence generator shift register
Ishift2=I_PN_state2;

%assign the stage values of Q pilot PN Sequence generator shift register
Qshift2=Q_PN_state2;

%make two arrays to hold the I and Q bit streams of data each stream hold a total of 12288 bits

outI2=zeros([1,12288]);
outQ2=zeros([1,12288]);
 
%seperate the I and Q streams
for i=1:12288

   %I=1 when I>0
   if real(combined(i))>=0
       outI2(i)=1;
   end
 
   %I=0 when I<0
   if real(combined(i))<0
       outI2(i)=0;
   end

  %Q=1 when Q>0
   if imag(combined(i))>=0
       outQ2(i)=(1*sqrt(-1));
       outQ2(i)=imag(outQ2(i));
   end
 
   %Q=0 when Q<0
   if imag(combined(i))<0
       outQ2(i)=(0*sqrt(-1));
       outQ2(i)=imag(outQ2(i));
   end

end

for i=1:12288

   outI2(i)=mod((outI2(i)+Ishift2(15)),2);
   outQ2(i)=mod((outQ2(i)+Qshift2(15)),2);

   %The 	I and Q pilot PN sequence generating polynomials
   %I=x^15+x^13+x^9+x^8+x^7+x^5+1
   %Q=x^15+x^12+x^11+x^10+x^6+x^5+x^4+x^3+1

    %We calculate The Q LFSR feedback vaule
    Ifeed2=mod((Ishift2(15)+Ishift2(13)+Ishift2(9)+Ishift2(8)+Ishift2(7)+Ishift2(5)),2);

    %then we do it for I
    Qfeed2=mod((Qshift2(15)+Qshift2(12)+Qshift2(11)+Qshift2(10)+Qshift2(6)+Qshift2(5)+Qshift2(4)+Qshift2(3)),2);

    %shifting
    Ishift2(2:15)=Ishift2(1:14);
    Qshift2(2:15)=Qshift2(1:14);

     %we then perform shifting for the two LFSRS
     Ishift2(1)=Ifeed2;
     Qshift2(1)=Qfeed2;

end

IQout= [outI2;outQ2];
R_received=IQout(:)';