载波频率偏移（Carrier Frequency Offset，CFO）：发射机和接收机本振频率之差，会造成接收到的I/Q采样值的相位旋转。This symptom of this offset is a phase rotation of incoming I/Q samples (time domain). The CFO can be corrected with the help of short preamble (Coarse) long preamble (Fine).
采样频率偏移（Sampling Frequency Offset，SFO）：AD采样器件的影响，会造成星座点的相位旋转。The symptom of this offset is a phase rotation of constellation points after FFT (frequency domain). The SFO can be corrected using the pilot sub-carriers in each OFDM symbol.
1. Coarse CFO Correction
粗载波频率偏移可以使用短序文估计：
在得到后，包括长序文之后的I/Q采样值需要被修正：
2. Fine CFO Correction
关于载波频率偏移更细的估计可以通过长序文中的长训练序列得到。
长序文包含了两个长训练序列，相位偏移可以计算得到：
This step is omitted in OpenOFDM due to the limited resolution of phase estimation and rotation in the look up table.
GitHub - jhshi/openofdm: Sythesizable, modular Verilog implementation of 802.11 OFDM decoder.
