filer_qpsk3.m

cdma 系统级仿真

%升余弦滤波器+QPSK调制
%已生成QPSK和OQPSK信号，本文件研究滤波器频谱
clc;%清除命令窗口
clear all;%清除工作空间workspace,以释放内存
close all;
%生成随机数
x_length=1000;                       %  信息码元个数
Rb=819200;%码元速率819.2k
k=1;                %一个码元间隔包括1个载波周期/2
k2=8;
fc=k*Rb;                             %  载波频率，
fs=fc*k2;                             %  信号采样率
x_size=k*k2;
%y=1:x_size;                         %  采样时间序列，每个码元采x_size点
x_i=randsrc(1,x_length,[-1,1]);%sign(rand(1,x_length)-0.5);       正负号函数sign，产生随机码
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);%将码元展宽x_size倍
    baseband_q(1,1+(i-1)*x_size:i*x_size)=x_q(i);%将码元展宽x_size倍
end
%将i路提前半个码元，相当于将q路延迟半个码元
%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));

%基带滤波
filtout_I= rcosflt(x_i,1,x_size,'fir',0.2);%利用现成的升余弦函数
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)';
%将i路提前半个码元，相当于将q路延迟半个码元
filtoutforeI=zeros(1,length(filtoutI));
filtoutforeI(1:length(filtoutI)-x_size/2)=filtoutI(x_size/2+1:length(filtoutI));
%n=15;%滤波器阶数
%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;

%产生载波
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调制
s_i=filtoutI.*carry_i;
s_q=filtoutQ.*carry_q;
sfore_i=filtoutforeI.*carry_i;
%输出QPSK信号
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后数据点数目,d = size(X)返回二维向量，分别为矩阵X行数和列数
f=1:fs/n:fs;
m=fc/fs*n*2;       %此处m=fs/4=2fc
 %图1,调制信号频谱图
figure(1)
subplot(3,1,1)
plot(f(1,1:m),fft_baseband_q(1,1:m))
title('基带信号频谱')
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('调制信号频谱')
grid on