Research On Time-Frequency Synchronization Technology Of Coherent Optical FBMC System

In recent years,the development of optical fiber communication is very rapid,and the people's demand for the communication with ultra-high-speed and large-capacity has continued to rise.In response to this change,the filter bank multi-carrier system(FBMC)was introduced into the mobile communication industry as an alternative to an orthogonal frequency division multiplexing(OFDM)system.Compared with OFDM system,FBMC has the following advantages: the out-of-band spectrum leakage is small;no cyclic prefix is needed,so the spectrum efficiency is high;it has the good time-frequency focusing characteristics;and the time-frequency grid is flexible and variable.However,like the OFDM system,the FBMC system is easily affected by the symbol time offset and carrier frequency offset.Due to the special signal modulation principle,the multiple symbol waveforms of FBMC will overlap in time.This will make the time synchronization very difficult,greatly reduce the performance of the system,and adversely affect the subsequent frequency offset estimation.Therefore,the accurate estimates of these offsets are important.This paper studies and analyzes the training-sequence-based timing and frequency synchronization algorithms for FBMC.In terms of the timing-offset estimation,a new timing synchronization method is designed for a coherent optical filter bank multi-carrier communication system(CO-FBMC/OQAM).This method firstly proposes and analyzes a training sequence structure that satisfies conjugate symmetry,and then inserts it in the frequency domain.Finally,at the receiving end,a timing metric function is used to perform the synchronous estimation and find the correct symbol timing position.In terms of the frequency offset estimation,this paper studies an integer frequency offset estimation and compensation method for a CO-FBMC/OQAM system,which is suitable for the circumstance with large frequency offset.As the first step of the algorithm,the previous research work on the fractional frequency offset has been extended.The training sequence was redesigned to have a hybrid structure.Using this training sequence,not only the fractional frequency offset can be effectively estimated,but also the integer frequency offset can be accurately calculated.In the second step,the effectiveness and accuracy of this method were studied by numerical simulation for the CO-FBMC/OQAM system.The obtained results show that the integer frequency offset estimation range can reach 12 times the subcarrier frequency interval.After the compensation for frequency offset,the system's bit error rate would quickly drop below the FEC limit.Therefore,the carrier frequency estimation method proposed by us can provide a useful reference for the future development and research of CO-FBMC/OQAM system,and has the practical value for the modern communication technology.