%DSSS 系統的仿真；
clc;
clear;
Fs=614400;                      %碼片速率
Nsam=8;                             %每碼片采樣點數;
N=128;                                  %擴頻因子;
FrameLength=100;				%幀長;
Data_I=randsrc(1,FrameLength,[-1,1]);
Data_Q=randsrc(1,FrameLength,[-1,1]);
PN=[0	0	0	0	0	0	0	1	0	0	1	0	0	1	1	0	1	0	0	1	1	1	1	0	1	1	1	0	0	0	0	1	1	1	1	1	1	1	0	0	0	1	1	1	0	1	1	0	0	0	1	0	1	0	0	1	0	1	1	1	1	1	0	1	0	1	0	1	0	0	0	0	1	0	1	1	0	1	1	1	1	0	0	1	1	1	0	0	1	0	1	0	1	1	0	0	1	1	0	0	0	0	0	1	1	0	1	1	0	1	0	1	1	1	0	1	0	0	0	1	1	0	0	1	0	0	0	1];

%每符號128×8個樣點
Data_sam=[1];
for i=1:length(Data_I)
    temp=[];
    for j=1:N*Nsam
        temp(j)=Data_I(i);
    end;
    Data_sam=[Data_sam temp];
end;
I_sam=Data_sam(2:length(Data_sam));

Data_sam=[1];
for i=1:length(Data_Q)
    temp=[];
    for j=1:N*Nsam
        temp(j)=Data_Q(i);
    end;
    Data_sam=[Data_sam temp];
end;
Q_sam=Data_sam(2:length(Data_sam));

%每碼片8個樣點
stuff = zeros(1,Nsam-1);
for i=1:N
    M_sam8((i-1)*Nsam+1) = 2*PN(i)-1;
    M_sam8 = [M_sam8 stuff];
end;


%設計碼片匹配濾波器；
R=1.0;                                  	%滾降系數為1
n_T=[-4 4];                             	%截短符號數為8;
rate=Nsam;                              	%每符號采樣點數為4;
T=1;
b=rcosfir(R,n_T,rate,T,'sqrt');     	%平方根升余弦濾波器；

%對數據進行擴展。
M_temp=M_sam8;
for i=1:FrameLength-1
    M_temp=[M_temp M_sam8];
end;
I_spread=I_sam.*M_temp;
Q_spread=Q_sam.*M_temp;

%碼片成型濾波
IS_filter=filter2(b,I_spread,'same');
QS_filter=filter2(b,Q_spread,'same');

figure;
subplot(3,1,1);
plot(IS_filter(1:300));
title('I路擴頻信號');
subplot(3,1,2);
plot(QS_filter(1:300));
title('Q路擴頻信號');
subplot(3,1,3);
plot(M_sam8(1:300));
title('擴頻序列');