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function output_frame = demodulation(input_modu, index) 
% demodulation for IEEE802.11a 
% Input:    input_modu, complex values representing constellation points 
%           index 
% Output:   output_frame, output bit stream (data unit is one bit) 
 
% In this version, increase the quatilization levels into 8. 
% note: Matlab index starts from 1 
Q_length=length(input_modu); 
QAM_input_I = real(input_modu); 
QAM_input_Q = imag(input_modu); 
output_frame = zeros(1,length(input_modu)*index); 
switch index 
case 1, 
    BPSK_Demodu_I = [0 1];      %f(m)=(m+1)/2 + 1, so I=-1 ---> 1, I=1 ---> 2 
    idx = find(QAM_input_I>1); 
    QAM_input_I(idx) = 1; 
    idx = find(QAM_input_I<-1); 
    QAM_input_I(idx) = -1; 
    output_frame = BPSK_Demodu_I(round((QAM_input_I+1)/2) + 1); 
case 2, 
    QPSK_Demodu_IQ = [0 1];     %f(m)=(m+1)/2 + 1, so I=-1 ---> 1, I=1 ---> 2 
    idx = find(QAM_input_I>1); 
    QAM_input_I(idx) = 1; 
    idx = find(QAM_input_I<-1); 
    QAM_input_I(idx) = -1; 
    idx = find(QAM_input_Q>1); 
    QAM_input_Q(idx) = 1; 
    idx = find(QAM_input_Q<-1); 
    QAM_input_Q(idx) = -1; 
    output_frame(1:2:end) = QPSK_Demodu_IQ(round((QAM_input_I+1)/2) + 1); 
    output_frame(2:2:end) = QPSK_Demodu_IQ(round((QAM_input_Q+1)/2) + 1); 
case 3, 
    remapping=[0 0 0;0 0 1;0 1 0;0 1 1;1 0 0;1 0 1;1 1 0;1 1 1].'; 
    for i=1:Q_length 
    phase_det=[2 1, I=1 ---> 3 
    idx = find(QAM_input_I>3); 
    QAM_input_I(idx) = 3; 
    idx = find(QAM_input_I<-3); 
    QAM_input_I(idx) = -3; 
    idx = find(QAM_input_Q>3); 
    QAM_input_Q(idx) = 3; 
    idx = find(QAM_input_Q<-3); 
    QAM_input_Q(idx) = -3; 
    tmp = round((QAM_input_I+3)/2) + 1; 
    output_frame(1:4:end) = bitget(QAM_16_Demodu_IQ(tmp),2); 
    output_frame(2:4:end) = bitget(QAM_16_Demodu_IQ(tmp),1); 
    tmp = round((QAM_input_Q+3)/2) + 1; 
    output_frame(3:4:end) = bitget(QAM_16_Demodu_IQ(tmp),2); 
    output_frame(4:4:end) = bitget(QAM_16_Demodu_IQ(tmp),1); 
case  5, 
     remapping=[0 0 0 0 0;0 0 0 0 1;0 0 0 1 0;0 0 0 1 1;0 0 1 0 0;0 0 1 0 1;0 0 1 1 0;0 0 1 1 1; 
                0 1 0 0 0;0 1 0 0 1;0 1 0 1 0;0 1 0 1 1;0 1 1 0 0;0 1 1 0 1;0 1 1 1 0;0 1 1 1 1; 
                1 0 0 0 0;1 0 0 0 1;1 0 0 1 0;1 0 0 1 1;1 0 1 0 0;1 0 1 0 1;1 0 1 1 0;1 0 1 1 1; 
                1 1 0 0 0;1 1 0 0 1;1 1 0 1 0;1 1 0 1 1;1 1 1 0 0;1 1 1 0 1;1 1 1 1 0;1 1 1 1 1].'; 
    for i=1:Q_length 
    phase_det=[4 1, I=1 ---> 5 
    idx = find(QAM_input_I>7); 
    QAM_input_I(idx) = 7; 
    idx = find(QAM_input_I<-7); 
    QAM_input_I(idx) = -7; 
    idx = find(QAM_input_Q>7); 
    QAM_input_Q(idx) = 7; 
    idx = find(QAM_input_Q<-7); 
    QAM_input_Q(idx) = -7; 
    tmp = round((QAM_input_I+7)/2) + 1; 
    output_frame(1:6:end) = bitget(QAM_64_Demodu_IQ(tmp),3); 
    output_frame(2:6:end) = bitget(QAM_64_Demodu_IQ(tmp),2); 
    output_frame(3:6:end) = bitget(QAM_64_Demodu_IQ(tmp),1); 
    tmp = round((QAM_input_Q+7)/2) + 1; 
    output_frame(4:6:end) = bitget(QAM_64_Demodu_IQ(tmp),3); 
    output_frame(5:6:end) = bitget(QAM_64_Demodu_IQ(tmp),2); 
    output_frame(6:6:end) = bitget(QAM_64_Demodu_IQ(tmp),1); 
end