Optical OFDM system adopting non data aided frequency offset estimation algorithm

Abstract

The invention provides an optical OFDM system adopting a non data aided frequency offset estimation algorithm. The optical OFDM system comprises an OFDM sending end, up-conversion, a DAC, optical modulation, optical fiber transmission, a variable optical attenuator, an optical detector, an ADC and an OFDM receiving end, the OFDM sending end generates a baseband OFDM signal; the OFDM receiving end comprises down-conversion, frequency offset estimation, secondary down-conversion, channel estimation and baseband frequency offset compensation, the frequency offset estimation divides a baseband OFDM time domain signal after the down-conversion with an absolute value to obtain a frequency offset factor containing sign bit influence, the frequency offset factor containing the sign bit influence is squared to eliminate the sign bit influence so as to obtain a 2 frequency-doubled frequency offset factor, an autocorrelation function of the frequency offset factor is figured out to eliminate the noise influence, a phase angle of the autocorrelation function is averaged to obtain a frequency offset estimator, the sampling frequency is adjusted, the down-conversion is carried out eliminate the envelope of frequency offset of up-conversion and down-conversion, and then channel estimation and frequency offset compensation are carried out. The optical OFDM system disclosed by the invention estimates the frequency offset without data assistance, and thus improving the data utilization rate.

Description

technical field [0001] The invention relates to an optical OFDM system used for estimating and compensating the influence on OFDM signal baseband and down-conversion frequency caused by frequency difference of sampling clock. Background technique [0002] In order to support multimedia services with rapidly emerging bandwidth requirements, such as high-definition television, online games, etc., the transmission capacity of the optical access network needs to be increased. Optical Orthogonal Frequency Division Multiplexing (OOFDM) is considered as a promising candidate technology for next-generation Passive Optical Networks (PON). Its inherent advantages include, for example, rich digital signal processing (DSP) implementations, high spectral efficiency, and flexible dynamic bandwidth allocation. Meanwhile, the OOFDM system with Intensity Modulation and Direct Detection (IMDD), has attracted a lot of attention in access scenarios due to its low DSP, complexity, stable perfor...

AI Technical Summary

Problems solved by technology

The disadvantage is that FFT is used to determine the frequency offset, the frequency resolution of FFT affects the accuracy, and the signal processing obtains the cosine signal of the absolute value, so it is impossible to determine whether it is a positive or negative frequency offset

[0006] The method disclosed in the research paper is only applicable to the baseband OFDM system, and does not consider the cosine envelope of the OFDM time-domain signal after up-down conversion due to the frequency difference of the sampling clock frequency. Because of the envelope, after FFT demodulation, not only The phase rotation caused by SFO, and the amplitude period change caused by the cosine envelope have a great impact on the performance of OFDM system

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