orthogonal_sampling.m

正交采样仿真程序

function [] = Orthogonal_sampling()
%%%%%%%%%%%%  正交采样程序  %%%%%%%%%%
%%%%%%%%%%%%%% 2007-11-29 %%%%%%%%%%%%
close all
clear all

f0=4200;  %载波频率
fs=4*f0; 
T= 0.5;    
t=-T/2:1/fs:T/2; 
A  = t+1;     
K = 400;             
theta =K*pi*t.^2;   
xr = A.*cos(2*pi*f0*t+theta);
xc = A.*exp(j*theta); 

figure(1)
subplot(2,1,1);plot(t,abs(xc));xlabel('时间(s)');ylabel('幅度');title('原始实信号理论复包络幅度')
subplot(2,1,2);plot(t,mod(angle(xc)*180/pi,360));xlabel('时间(s)');ylabel('幅度');title('原始实信号理论复包络相位')

figure(2);
F = -fs*floor(length(xr)/2)/length(xr):fs/(length(xr)):fs*floor(length(xr)/2)/length(xr);
fft_xr = 20*log10(abs(fft(xr)));
fft_xr = fft_xr(2:length(xr)/2+1);
fft_xr = [fliplr(fft_xr) fft_xr(1) fft_xr];
subplot(2,1,1);plot(t,xr);xlabel('时间(s)');ylabel('幅度');title('原始信号Xr时域波形')
subplot(2,1,2);plot(F,fft_xr);xlabel('频率(Hz)');ylabel('幅度(dB)');title('原始信号xr频谱');

%%%%%%%%%  30阶FIR滤波器  %%%%%%%%%%%%
n=30; f1=1/fs/fs; f2=f0/3;
Wn=[f1 f2]/(fs/2);
[fir1_b,fir1_a]=fir1(n,Wn);figure(3);freqz(fir1_b,fir1_a);

xc_a = 2*xr.*cos(2*pi*f0*t);  xc_a = filter(fir1_b,fir1_a,xc_a);
xc_b = 2*xr.*sin(2*pi*f0*t);  xc_b = filter(fir1_b,fir1_a,xc_b);
Fs =2*K;   
xc_a = xc_a(1:fs/Fs:length(xc_a));  %  同相分量采样
xc_b = xc_b(1:fs/Fs:length(xc_b));  %  正交分量采样
xc_out = xc_a+j*xc_b;

A_out = abs(xc_out);      
theta_out = mod(angle(xc_out)*180/pi,360);
t_out = -length(A_out)/Fs/2+1/Fs:1/Fs:length(A_out)/Fs/2;

figure(4)
subplot(2,1,1);plot(t_out,A_out);xlabel('时间(s)');ylabel('幅度');title('解调得到的信号复包络幅度');axis([-0.25,0.25,0,1.5]);
subplot(2,1,2);plot(t_out,theta_out);xlabel('时间(s)');ylabel('幅度');title(' 解调得到的信号复包络相位');axis([-0.25,0.25,0,400]);