clear;
Fd=1;                                              %消息序列的采樣速率
Fs=4*Fd;                                         %已調信號的采樣速率
M=8;
for  SNR_db=0:10:20
Eb_N0=10^(SNR_db/10);
sgma=sqrt(1/(8*Eb_N0));           %nc、ns的均方差
x=randint(10,1,M);                      %產生隨機消息序列
y=dmodce(x,Fd,Fs, 'psk',M);            %PSK調制
ynoise=y+sqrt(Fs/Fd)*sgma*(randn(length(y),1)+j*randn(length(y),1));      % 加噪
figure(SNR_db+1);
axis([-1.2 1.2 -1.2 1.2]);
hold on;
for i=0:M-1
   plot(cos(2*pi*i/M),sin(2*pi*i/M),  '.','MarkerSize' ,20);
end
plot(ynoise, '+');                                                  %畫出星座圖
hold  off;                                                              %畫出受到噪聲干擾的信號向量；
end;