% bpsk.m
% Simulation program to realize BPSK transmission system
%
% 這個程序仿真了數字信號的BPSK調制及相關解調，
% 傳輸信道為加性高斯白噪聲信道（AWGN）

%******************** Preparation part **********************

sr=256000.0; % Symbol rate
ml=1;        % Number of modulation levels
br=sr.*ml;   % Bit rate (=symbol rate in this case)
nd = 1000;   % Number of symbols that simulates in each loop
ebn0=3;      % Eb/N0,dBW
IPOINT=8;    % Number of oversamples
    
%******************** Data generation ********************************  

	indata=rand(1,nd)>0.5;  % rand: built in function

%******************** BPSK Modulation ***********************  

    data1=indata.*2-1;  % convert(0,1) to (-1,1)
    data2=zeros(1,nd*IPOINT);              % oversample data1,initiation
    data2(1:IPOINT:1+IPOINT*(nd-1))=data1; % set the date from data1 every 8 samples
	
%****************** Attenuation Calculation *****************
	
    spow=sum(data2.*data2)/nd;  % average symbol power
	npow=spow*sr/br*10.^(-ebn0/10); % noise power
	attn=sqrt(0.5*npow);  % the attenuation of AWGN noise

%************ Add White Gaussian Noise (AWGN) ***************
	
    inoise=randn(1,length(data2)).*attn;  % randn: built in function
	data3=data2+inoise;		
	data4=data3(1:IPOINT:IPOINT*nd-1);
    
%******************** BPSK Demodulation *********************

    outdata=data4>0;

%********************** Output result ***************************
% 輸入、輸出比特流的圖形對比
x=0:nd-1;
plot(x,indata,'b*-',x,outdata,'r-')
h=legend('indata','outdata');
set(gca,'ytick',[-1:2])
axis equal tight([0 inf 0 1])