clear;
Fd=1;%消息序列的采樣速率
Fs=3*Fd;%已調信號的采樣速率
M=4;%M進制的PSK調制
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));%加噪聲
    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);%畫星座圖
    end
    plot(ynoise,'+');%畫出受到干擾的信號向量
    hold off;
end;