filer_qpsk.m

cdma 系统级仿真

%升余弦滤波器+PSK调制,%已生成QPSK和OQPSK信号
function y=filer_QPSK(a,b)%
%生成随机数
%x_length=10;                       %  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
k2=16;
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=a;
x_q=b;
x_length=length(a);
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
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;
y=soqpsk;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
figure(2)
subplot(3,1,1)
plot(filtoutforeI(1:20*x_size))                   
axis([0 x_size*20 -1.5 1.5])
grid on
title('I路码元信号')

subplot(3,1,2)
plot(filtoutQ(1:20*x_size))         
axis([0 x_size*20 -1.5 1.5])
title('Q路码元信号')
grid on
subplot(3,1,3)
plot(carry_i(1:20*x_size))               %显示调制信号波形
axis([0 x_size*20 -1.5 1.5])
title('载波')
grid on

figure(4)
subplot(3,1,1)
plot(sfore_i(1:20*x_size))                   %显示基带信号波形
axis([0 x_size*20 -1.5 1.5])
grid on
title('I路BPSK调制信号')
subplot(3,1,2)
plot(s_q(1:20*x_size))          %显示载波信号波形
axis([0 x_size*20 -1.5 1.5])
title('Q路BPSK调制信号')
grid on
subplot(3,1,3)
plot(soqpsk(1:20*x_size))               %显示调制信号波形
axis([0 x_size*20 -1.5 1.5])
title('OQPSK调制信号')
grid on