demodulator.m

These files in Matlab implement a conventional DS -CDMA detector using QPSK modulation and matched f

% Demodulator , which multiplies the input signals with sin and cos and
% also takes care of the PN sequences

function [amp_estimate]=demodulator(mod_sig)

global Fs Fc Ts Nsamp Tb pn_seqI pn_seqQ  t 

demod_signal_1=mod_sig.*cos(2*pi*Fc*t);
demod_signal_2=mod_sig.*sin(2*pi*Fc*t);


op_int_1=intdump(demod_signal_1,Nsamp*2);
op_int_2=intdump(demod_signal_2,Nsamp*2);

xQ_recv=op_int_1;     % Received odd sequence
xI_recv=op_int_2;     % Received even sequence

xQ_recv=xQ_recv.*pn_seqQ;   % Note that both pn_seqI and XI are in polar form
xI_recv=xI_recv.*pn_seqI;

x_recv=[];            
x_recv(2:2:2*length(xI_recv))=xI_recv;
x_recv(1:2:2*length(xQ_recv))=xQ_recv;   % Received signal ( still has the Walsh codes in them )

amp_estimate=x_recv;