由于QAM采用幅度和相位二维调制，其频谱效率大大提高，而且不同点的欧式距离也要大于调幅AM调制方式，QAM也是LTE和5G NR首选的调制方式，本期教大家画一个64QAM的星座图。

如下：

首先产生一个64QAM的调制数据，幅度归一化

SymbolAlphabet = [

    complex( 3,  3)

    complex( 3,  1)

    complex( 1,  3)

    complex( 1,  1)

    complex( 3,  5)

    complex( 3,  7)

    complex( 1,  5)

    complex( 1,  7)

    complex( 5,  3)

    complex( 5,  1)

    complex( 7,  3)

    complex( 7,  1)

    complex( 5,  5)

    complex( 5,  7)

    complex( 7,  5)

    complex( 7,  7) % symbol 0-15

    complex( 3, -3)

    complex( 3, -1)

    complex( 1, -3)

    complex( 1, -1)

    complex( 3, -5)

    complex( 3, -7)

    complex( 1, -5)

    complex( 1, -7)

    complex( 5, -3)

    complex( 5, -1)

    complex( 7, -3)

    complex( 7, -1)

    complex( 5, -5)

    complex( 5, -7)

    complex( 7, -5)

    complex( 7, -7) % symbol 16-31

    complex(-3,  3)

    complex(-3,  1)

    complex(-1,  3)

    complex(-1,  1)

    complex(-3,  5)

    complex(-3,  7)

    complex(-1,  5)

    complex(-1,  7)

    complex(-5,  3)

    complex(-5,  1)

    complex(-7,  3)

    complex(-7,  1)

    complex(-5,  5)

    complex(-5,  7)

    complex(-7,  5)

    complex(-7,  7) % symbol 32-47

    complex(-3, -3)

    complex(-3, -1)

    complex(-1, -3)

    complex(-1, -1)

    complex(-3, -5)

    complex(-3, -7)

    complex(-1, -5)

    complex(-1, -7)

    complex(-5, -3)

    complex(-5, -1)

    complex(-7, -3)

    complex(-7, -1)

    complex(-5, -5)

    complex(-5, -7)

    complex(-7, -5)

    complex(-7, -7) ] / sqrt(42); % symbol 48-63

%调用figure准备画一个图

figure;

给数据添加AWGN白噪声，SNR=33db

snrDb = 33;

% 每个星座点画100次相同SNR下的图

length = 100;

for n=1:length

% 调用awgn库函数为数据添加噪声

SymbolAlphabetTemp = awgn(SymbolAlphabet, snrDb);

%取数据的实部和虚部

    x_r = real(SymbolAlphabetTemp);

    x_i = imag(SymbolAlphabetTemp);

%画图   

 h = plot(x_r,x_i,'.');

%为图添加颜色

    set(h, 'Color', [0, 0.2,(n/length)]);

    hold on;

End

%添加标题和网格

title('64QAM 星座图');

grid on;

效果图如下：