www.pudn.com > demodulation1.rar > demodulation1.m

function output_frame = demodulation1(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);
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,
    mapping=[3+i 1+i -3+i -1+i -3-i -1-i 3-i 1-i];
    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].';
    a=ones(1,8);
    for j=1:Q_length
      b = mapping-input_modu(j)*a;
      [gk k1]=min(abs(b).^2);
      output_frame((1+(j-1)*3):(3+(j-1)*3))=remapping((1+3*(k1-1)):(3+3*(k1-1)));
    end 
case 4,
    QAM_16_Demodu_IQ = [0 1 3 2];   %f(m)=(m+3)/2 + 1, so I=-3 ---> 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,
    mapping=[5+i 3+i 1+i 5+3*i 3+3*i 1+3*i 3+5*i 1+5*i -5+i -3+i -1+i -5+3*i -3+3*i -1+3*i -3+5*i -1+5*i -5-i -3-i -1-i -5-3*i -3-3*i -1-3*i -3-5*i -1-5*i 5-i 3-i 1-i 5-3*i 3-3*i 1-3*i 3-5*i 1-5*i];
    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].';
    a=ones(1,32);
    for j=1:Q_length
      b = mapping-input_modu(j)*a;
      [gk k1]=min(abs(b).^2);
      output_frame((1+(j-1)*5):(5+(j-1)*5))=remapping((1+5*(k1-1)):(5+5*(k1-1)));
      end 

case 6,
    QAM_64_Demodu_IQ = [0 1 3 2 6 7 5 4];   %f(m)=(m+7)/2 + 1, so I=-7 ---> 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