function output_Q = Q(input, index)
% Input_modu: input bit stream (0,1)
% index:  modulation index
%		1---bpsk
%		2---qpsk
%		4---16qam
%		6---64qam
% 	else is error
QAM_input_I = real(input);
QAM_input_Q = imag(input);
% note: Matlab index starts from 1
switch index
case 1,
    %BPSK_I = [-1 1];    % refer to Table82 on page21 of IEEE802.11a
    QAM_input_I = sign(QAM_input_I);
case 2,
    %QPSK_IQ = [-1 1];   % refer to Table83 on page21 of IEEE802.11a
    QAM_input_I = sign(QAM_input_I);
    QAM_input_Q = sign(QAM_input_Q);
case 4,
   % QAM_16_IQ = [-3 -1 3 1];    % refer to Table84 on page21 of IEEE802.11a
    QAM_input_I = sign(QAM_input_I)+sign(QAM_input_I+2)+sign(QAM_input_I-2);
    QAM_input_Q = sign(QAM_input_Q)+sign(QAM_input_Q+2)+sign(QAM_input_Q-2);
%case 6,
%    QAM_64_IQ = [-7 -5 -1 -3 7 5 1 3];  % refer to Table85 on page21 of IEEE802.11a
%    QAM_input_I = QAM_64_IQ(input_frame(1:6:end)*4+input_frame(2:6:end)*2+input_frame(3:6:end)+1);
%    QAM_input_Q = QAM_64_IQ(input_frame(4:6:end)*4+input_frame(5:6:end)*2+input_frame(6:6:end)+1);
end
output_Q = QAM_input_I + j * QAM_input_Q;