Real-time Phase Tracking Method for IEEE 802.11a/g Receiver under Phase Noise Condition

摘要

In the IEEE802.11a/g system, frequency offset between a transmitter and a receiver is compensated using the preamble of the frame. Moreover, continuous frequency compensation is possible using pilot subcarriers in cases where the frequency offset varies in following data symbols. This continuous compensation is important since serious phase noise occurs in the frequency synthesizer of 5/2.4GHz, distorts OFDM symbols, and makes demodulation of 16QAM or 64QAM signals difficult. Recently the problem regarding phase noise has come one of the most prominent issues in development of radio communication systems. Conventionally, a method that measures the phase rotation of the signal using a pilot subcarrier and compensates the rotation by extrapolation is known. However, by the conventional method, a fast phase fluctuation cannot be followed since extrapolation mainly follows the constant phase rotation. Therefore, we propose a phase compensation method which can acquire good receiving characteristics also under phase noise environment. The proposed method applies both measured phase rotation of each OFDM symbol itself and the average of them with constant ratio. Then, tracking for both the steady and the fluctuated frequency offset becomes possible.