%QPSK调制与解调
%输出的串行数据比输入要延迟3个码元
clear;close all;clc;
Rate=20000;%串行信息比特率:20kbps
Frequency=60000;%载波频率:40kHz
N=127;%码元数量:127，必须是大于3的奇数
sample_point=40;%每个载波周期的采样点数，必须是8的整数倍
c1_sample=sample_point*Frequency/Rate;%每个串行码元的采样点数
c2_sample=c1_sample*2;%每个并行码元的采样点数
Fs=Frequency*sample_point;%采样率
T=1/Fs;%采样周期
t=T:T:N/Rate;
L=sample_point*N*Frequency/Rate;%总的采样点数
sim('qpsk_sim');
original=original(1:end-1);
plot(t,original);
ylim([-1.1,1.1]);
title('基带信号时域波形');
% Pxx1=periodogram(original);
Pxx1=abs(fft(original)/L).^2*Rate/2/N;
L_f=length(Pxx1);
f=Fs/L_f:Fs/L_f:Fs;
figure;
plot(f,Pxx1);
xlabel('频率/Hz');
title('基带信号功率谱密度');
modulate=modulate(c1_sample+1:end-1);
figure;
plot(t(1:end-c1_sample),modulate);
title('已调信号时域波形');
% Pxx2=periodogram(modulate);
Pxx2=abs(fft(modulate)).^2*Rate/2/N;
L_f=length(Pxx2);
f=Fs/L_f:Fs/L_f:Fs;
figure;
plot(f,Pxx2);
xlabel('频率/Hz');
title('已调信号功率谱密度');
demodulate=demodulate(3*c1_sample+1:end-1);
figure;
plot(t(1:end-3*c1_sample),demodulate);
ylim([-1.1,1.1]);
title('解调后的信号时域波形');
data_orig=zeros(1,N-3);
data_dem=zeros(1,N-3);
for num=1:N-3
data_orig(num)=original(c1_sample*(num-1)+1);
data_dem(num)=demodulate(c1_sample*(num-1)+1);
end
I_direction=I_direction(3*c1_sample+1:end-1);
Q_direction=Q_direction(3*c1_sample+1:end-1);
N_parallel=(N-3)/2;
x_dir=zeros(1,N_parallel);
y_dir=zeros(1,N_parallel);
for num=1:N_parallel
x_dir(num)=I_direction(2*c1_sample*(num-1)+1);
y_dir(num)=Q_direction(2*c1_sample*(num-1)+1);
end
figure;
scatter(x_dir,y_dir);
title('星座图');
