function [qam_out] = Qam4_mod(qam_in)
%% 4QAM 調制函數
%% 輸入： 矩陣，列數必須是4的倍數，01序列
%% 輸出： 矩陣，4qam調制后的矩陣
global QamTable
global bitPerSymbol;
QamTable = [ -1-i, 1-i, -1+i, 1+i ];
[ m, n ] = size(qam_in);
qam_out = zeros(m,n/bitPerSymbol);
for k = 1:m
    QamTmp = reshape(qam_in(k,:),bitPerSymbol,n/bitPerSymbol)';
    QamTmpTmp = bi2de( QamTmp, 'left-msb');
    qam_out(k, :) = QamTable( QamTmpTmp+1 );
end