xbianpin.asv

就是qpsk用matlab实现调制解调以及扩频接扩

%下变频的过程
%先乘本地载波后再经过低通滤波器
function R2=xbianpin(R,ft,N,Ts)
T=0.001/N;
tdi=0:2*Ts:N*T-Ts;
s1=R.*cos(2*pi*ft*tdi);



sss=fft(s1,1024);
w=(0:511)/512*(fs/4);
figure(20)
plot(w,abs(S1(1:512)'));
title('解调时乘完载频的' );
set(gcf,'color' ,'white' );
xlabel(' Frequency(Hz)' );
ylabel(' Mag.of frequency response' ); grid;



%设计滤波器
fs=1/Ts;
[b,a]=ellip(4,0.4,150,3e6*2/Fs,'low'); %得到滤波器的系数矩阵
k2=filter(b,a,s1)
figure(4)
subplot(212);
plot(tdi,k2);
title('去载波后的I+Q图形');
xlabel('时间坐标tdi');
kk=fft(k2,1024); %求出原始信号的傅立叶变换
w=(0:511)/512*(fs/4);
figure(21)
plot(w,abs(kk(1:512)'));
title(' 滤波前' );
set(gcf,'color' ,'white' );
xlabel(' Frequency(Hz)' );
ylabel(' Mag.of frequency response' ); grid;

figure(4);
subplot(212);
plot(tdi,R2);
axis([0 0.001 -2 2]);
title('去载波后的s(t)图形');
xlabel('时间坐标                             t');
ylabel('amplitude');
end