SNR_DB=[0:1:12]; %Signal-to-noise ratio gradually improve

sum=1000000;

data= randsrc(sum,2,[0 1]); %等概產(chǎn)生1000000*2的矩陣：0和1

[a1,b1]=find(data(:,1)==0&data(:,2)==0);  %找到第一列和第二列為0

message(a1)=-1-j; % map [ 0 0] to 225°

[a2,b2]=find(data(:,1)==0&data(:,2)==1);

message(a2)=-1+j; % map [ 0 1] to 135°

[a3,b3]=find(data(:,1)==1&data(:,2)==0);

message(a3)=1-j; % map [ 1 0] to 275°

[a4,b4]=find(data(:,1)==1&data(:,2)==1);

message(a4)=1+j;% map [ 0 0] to 45°

scatterplot(message)

title('B點(diǎn)信號(hào)的星座圖')

A=1;

Tb=1;

Eb=A*A*Tb;%帶寬w=1hz

P_signal=Eb/Tb;

NO=Eb./(10.^(SNR_DB/10)); %SNR_DB=10.*log10(Eb./NO)

P_noise=NO; %noise power 單邊功率譜密度(N0)主要用在復(fù)數(shù)信號(hào)中，雙邊功率譜密度(N0/2)主要用在實(shí)信號(hào)中。

sigma=sqrt(P_noise);           

for Eb_NO_id=1:length(sigma) 

    noise1=sigma(Eb_NO_id)*randn(1,sum);  

    noise2=sigma(Eb_NO_id)*randn(1,sum); 

    receive=message+noise1+noise2*j; %how to add gaussian noise to the original signal

倒數(shù)第三行為什么是乘號(hào)而不是加號(hào)