qpsk.m

qpsk matlab

clear all;
close all;

M=4;
Ts=1;
fc=10;
N_sample=16;
N_num=100;

dt=1/fc/N_sample;
t=0:dt:N_num*Ts-dt;
T=dt*length(t);

py1f=zeros(1,length(t));
py2f=zeros(1,length(t));

for PL=1:100;
    d1=sign(randn(1,N_num));
    d2=sign(randn(1,N_num));
    gt=ones(1,fc*N_sample);
    
    s1=sigexpand(d1,fc*N_sample);
    s2=sigexpand(d2,fc*N_sample);
    b1=conv(s1,gt);
    b2=conv(s2,gt);
    s1=b1(1:length(s1));
    s2=b2(1:length(s2));
    
    st_qpsk=s1.*cos(2*pi*fc*t)-s2.*sin(2*pi*fc*t);
    
    s2_delay=[-ones(1,N_sample*fc/2) s2(1:end-N_sample*fc/2)];
    st_oqpsk=s1.*cos(2*pi*fc*t)-s2_delay.*sin(2*pi*fc*t);
    
    [f y1f]=T2F(t,st_qpsk);
    [f y2f]=T2F(t,st_oqpsk);
    [t y1]=bpf(f,y1f,fc-1/Ts,fc+1/Ts);
    [t y2]=bpf(f,y2f,fc-1/Ts,fc+1/Ts);
    subplot(221)
    plot(t,y1);
    xlabel('t');
    ylabel('QPSK波形')
    axis([5 15 -0.5 0.5]);
    title('经过带通后波形');
    
    subplot('222')
    plot(t,y2);
    xlabel('t');
    ylabel('OQPSK波形');
    axis([5 15 -0.5 0.5]);
    title('经过带通后波形')
    
    y1=1.5*tanh(2*y1);
    y2=1.5*tanh(2*y2);
    [f y1f]=T2F(t,y1);
    [f y2f]=T2F(t,y2);
    py1f=py1f+abs(y1f).^2/T;
    py2f=py2f+abs(y2f).^2/T;
end
py1f=py1f/100;
py2f=py2f/100;

subplot(223)
plot(f,10*log10(py1f));
xlabel('f');
ylabel('QPSK功率频谱密度(dB/HZ)');
title('经过线形电路后的功率频谱密度');
axis([-15 15 -30 10]);

subplot(224)
plot(f,10*log10(py2f));
xlabel('f');
ylabel('OQPSK功率频谱密度(dB/HZ)');
title('经过非线形电路后的功率频谱密度');
axis([-15 15 -30 10]);

figure(2)
x=-2:0.1:2;
y=1.5*tanh(2*x);
plot(x,y);
title('非线形电路输入函数')