% OQPSK Demodulation
clear,close,clc

ErrBit = 0;
ErrBitDigital = 0;

SNR = -10;
NumData = 1000;

Debug = 0;

% 1 OQPSK調(diào)制
t = 0:pi/20:20*pi;

data = 1*pi/4;

tx = cos(t + data);



for f = 1:NumData
% 2 信道傳輸
for j = 1:max(size(t))
    noise(j) = randn;
end

meanNoise = 10^(-SNR/20) * mean(noise);

rx = tx + 10^(-SNR/20) * noise;

% 3 OQPSK解調(diào)

vcoi = cos(t);
vcoq = sin(t);

ipath = vcoi.* rx;
qpath = vcoq.* rx;

idec = mean(ipath) + randn;
qdec = mean(qpath) + randn;

% 4 數(shù)字采樣解調(diào)
indexI = find(mod(t, pi) == 0);
indexQ = find(mod(t, pi) == pi/2);

idecDigtal = sum(ipath(1,indexI));
qdecDigtal = sum(qpath(1,indexQ));

%plot(ipath);
%hold
%plot(qpath,'r')

% 5  誤碼率分析
if((idec <=0) || qdec >= 0)
    ErrBit = ErrBit + 1
end

%if((idecDigtal <=0) || qdecDigtal >= 0)
if((idecDigtal <=0) || (qdecDigtal >= 0))
    ErrBitDigital = ErrBitDigital + 1
    sumNoise(ErrBitDigital + 1,1) = sum(noise(indexI));
    sumNoise(ErrBitDigital + 1,2) = sum(ipath(1,indexI));
    
    if (Debug == 1)
        ClearChn = tx(indexI).*vcoi(indexI)
        NoiseSap = noise(indexI)

        NoiseChn = rx(indexI).*vcoi(indexI)
        sumClearChn = sum(ClearChn)
        sumNoiseChn = sum(NoiseChn)
        sumNoiseSap = sum(NoiseSap)
        error('Debug On');
    end
        
end


end

sumNoise
BER = ErrBit/NumData
ErrBitDigital = ErrBitDigital/NumData