function st_coded = st_coding( mod_sym,N_Tx_ant,ST_Code)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% 發送分集 , 2發或4發

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


[N_subc,N_sym] = size(mod_sym);

% 如果有發送分集
if N_Tx_ant ~= 1
% 使用空時分組碼
    if ST_Code == 1
        st_coded = zeros(N_subc,N_sym, N_Tx_ant);
        if (mod(N_sym,N_Tx_ant))
            error('空時編碼器輸入符號不匹配,子程序st_coding出錯');
        else
            for n = 1:N_sym/N_Tx_ant    
                % 一次送入空時編碼器的OFDM符號有N_Tx_ant個
                coded_tmp = stbc_code_TX( mod_sym( :,(n-1)*N_Tx_ant+1 : n*N_Tx_ant ) );
                % coded_tmp的結構: 每列代表一條天線發出的數據,有N_Tx_ant*N_subc
               % 個樣點, 而一共有N_Tx_ant列,代表不同天線的數據
               % 轉化為結構:有 N_subc行, 代表不同時間OFDM符號的N_Tx_ant列, 
               % 矩陣第三維為N_Tx_ant個,代表不同天線的數據
                for ant = 1:N_Tx_ant
                     tmp = reshape(coded_tmp(:,ant), N_subc, N_Tx_ant);
                     % 把調整后的符號塊,放在輸出符號的相應位置
                     st_coded(:, (n-1)*N_Tx_ant+1:n*N_Tx_ant ,ant) = tmp;
                end
            end
        end

    % 使用空時格碼
    elseif ST_Code == 2
    
    
    end

% 如果沒有發送分集
else
    st_coded = mod_sym;
end