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function output_modu = modulation(input_frame, index) 
% Input_modu: input bit stream (0,1) 
% index:  modulation index 
%		1---bpsk 
%		2---qpsk 
%		4---16qam 
%		6---64qam 
% 	else is error 
f_length = length(input_frame)/index; 
QAM_input_I = zeros(1,f_length); 
QAM_input_Q = zeros(1,f_length); 
% 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 = BPSK_I(input_frame+1); 
    output_modu = QAM_input_I ; 
case 2, 
    QPSK_IQ = [-1 1];   % refer to Table83 on page21 of IEEE802.11a 
    QAM_input_I = QPSK_IQ(input_frame(1:2:end)+1); 
    QAM_input_Q = QPSK_IQ(input_frame(2:2:end)+1); 
    output_modu = QAM_input_I + j * QAM_input_Q; 
case 3, 
    mapping=[3+i 1+i -3+i -1+i -3-i -1-i 3-i 1-i ]; 
    output_modu=mapping(input_frame(1:3:end)*4+input_frame(2:3:end)*2+input_frame(3:3:end)+1); 
case 4, 
    QAM_16_IQ = [-3 -1 3 1];    % refer to Table84 on page21 of IEEE802.11a 
    QAM_input_I = QAM_16_IQ(input_frame(1:4:end)*2+input_frame(2:4:end)+1); 
    QAM_input_Q = QAM_16_IQ(input_frame(3:4:end)*2+input_frame(4:4:end)+1); 
    output_modu = QAM_input_I + j * QAM_input_Q; 
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]; 
    output_modu=mapping(input_frame(1:5:end)*16+input_frame(2:5:end)*8+input_frame(3:5:end)*4+input_frame(4:5:end)*2+input_frame(5:5:end)+1); 
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); 
    output_modu = QAM_input_I + j * QAM_input_Q; 
end