fre

说明：  此为频偏校正程序,通过TD_GG算法得到的频偏值还存在几赫兹的残余频偏，这里，我们可以通过反馈算法进行校正，以得到更加精确的频偏值。(for this frequency offset correction procedure for the adoption of the algorithm TD_GG Frequency values still exist remnants of a few hertz frequency offset, here, we can pass feedback correction algorithm, to be more precise frequency offset value.)