%升余弦濾波器+QPSK調制
%已生成QPSK和OQPSK信號，本文件研究濾波器頻譜
clc;%清除命令窗口
clear all;%清除工作空間workspace,以釋放內存
close all;
%生成隨機數
x_length=1000;                       %  信息碼元個數
Rb=819200;%碼元速率819.2k
k=1;                %一個碼元間隔包括1個載波周期/2
k2=8;
fc=k*Rb;                             %  載波頻率，
fs=fc*k2;                             %  信號采樣率
x_size=k*k2;
%y=1:x_size;                         %  采樣時間序列，每個碼元采x_size點
x_i=randsrc(1,x_length,[-1,1]);%sign(rand(1,x_length)-0.5);       正負號函數sign，產生隨機碼
x_q=randsrc(1,x_length,[-1,1]);
for i=1:x_length
%    baseband_i(1,1+(i-1)*x_size:i*x_size)=x_i(i);%將碼元展寬x_size倍
    baseband_q(1,1+(i-1)*x_size:i*x_size)=x_q(i);%將碼元展寬x_size倍
end
%將i路提前半個碼元，相當于將q路延遲半個碼元
%basefore_i=zeros(1,length(baseband_i));
%basefore_i(1:length(baseband_i)-x_size/2)=baseband_i(x_size/2+1:length(baseband_i));

%基帶濾波
filtout_I= rcosflt(x_i,1,x_size,'fir',0.2);%利用現成的升余弦函數
filtout_Q= rcosflt(x_q,1,x_size,'fir',0.2);
filtoutI=filtout_I(2.5*x_size+1:x_length*x_size+2.5*x_size)';
filtoutQ=filtout_Q(2.5*x_size+1:x_length*x_size+2.5*x_size)';
%將i路提前半個碼元，相當于將q路延遲半個碼元
filtoutforeI=zeros(1,length(filtoutI));
filtoutforeI(1:length(filtoutI)-x_size/2)=filtoutI(x_size/2+1:length(filtoutI));
%n=15;%濾波器階數
%shengyuxuian=myfilter(n,k2);
%filtoutI=filter(shengyuxuian,1,baseband_i);
%filtoutQ=filter(shengyuxuian,1,baseband_q);
%filtoutforeI=filter(shengyuxuian,1,basefore_i);

%baseband_i(2,:)=filtoutI;
%baseband_q(2,:)=filtoutQ;

%產生載波
carry_i(1:x_length*x_size)=cos(2*pi*fc*(1:x_length*x_size)/fs+pi/4); 
carry_q(1:x_length*x_size)=sin(2*pi*fc*(1:x_length*x_size)/fs+pi/4); 
%BPSK調制
s_i=filtoutI.*carry_i;
s_q=filtoutQ.*carry_q;
sfore_i=filtoutforeI.*carry_i;
%輸出QPSK信號
sqpsk=s_i+s_q;
soqpsk=sfore_i+s_q;

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
fft_baseband_q=abs(fft(baseband_q));             
fft_filtoutI=abs(fft(filtoutQ));             
fft_soqpsk=abs(fft(soqpsk));             
n=size(soqpsk,2);%FFT后數據點數目,d = size(X)返回二維向量，分別為矩陣X行數和列數
f=1:fs/n:fs;
m=fc/fs*n*2;       %此處m=fs/4=2fc
 %圖1,調制信號頻譜圖
figure(1)
subplot(3,1,1)
plot(f(1,1:m),fft_baseband_q(1,1:m))
title('基帶信號頻譜')
grid on
subplot(3,1,2)
plot(f(1,1:m),fft_filtoutI(1,1:m))
title('')
grid on
subplot(3,1,3)
plot(f(1,1:m),fft_soqpsk(1,1:m))
title('調制信號頻譜')
grid on