function [qam_out] = Qam4_demod(qam_in)
%% 4QAM 解調函數
%% 輸入： 矩陣，列數必須是的的倍數
%% 輸出： 矩陣，解調后的01序列矩陣
%% 之前必須調用過
global QamTable;
global bitPerSymbol ;
[m,n] = size(qam_in);
qam_out = zeros(m,n*bitPerSymbol);
% 判決
for k = 1:m
    delt = abs(reshape(qam_in(k,:), n, 1)*ones(1,4) - ones(n,1)*QamTable);  %求最近的點
    [tmp, index] = min(delt,[],2);    %得到索引值
    qam_outTmp = de2bi(index-1,bitPerSymbol,'left-msb');
    qam_out(k,:) = reshape(qam_outTmp',1,bitPerSymbol*n);
end