function transmit_signal = ofdm_mod(pilot_added,PrefixRatio,N_subc,N_used,N_sym_ts,N_ts,...
    Idx_used,N_Tx_ant,AddChFreq)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 實(shí)現(xiàn)OFDM的基本調(diào)制

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

if ~AddChFreq
    
    transmit_signal = zeros(1,N_subc*N_sym_ts*N_ts*(1+PrefixRatio),N_Tx_ant);
    cp_len = round(PrefixRatio*N_subc);
    
    for ant = 1:N_Tx_ant
        % ifft乘sqrt(N_subc)以保證變換前后能量不變
        % 我們假設(shè)頻域的樣點(diǎn)是在[-fs/2  fs/2]中的, fs是采樣頻率
        % 使用fftshift函數(shù)目的是使得變換前的頻域樣點(diǎn)轉(zhuǎn)換到[0 fs]中,以滿足IFFT變換的要求
        ofdm_frame = sqrt(N_subc) * ifft( fftshift( pilot_added(:,:,ant), 1 ) );
        cp = ofdm_frame(N_subc - cp_len + 1:N_subc ,:);
        ofdm_frame = [cp;ofdm_frame];
        % 加窗處理
        
        % 轉(zhuǎn)換為串行信號(hào)
        transmit_signal(:,:,ant) = reshape( ofdm_frame, 1, N_subc * N_sym_ts * N_ts *(1+PrefixRatio) );    
    end
    
else
    transmit_signal = NaN;  % 如果頻域加信道，transmit_signal不存在. 賦值NaN以防止警告
end