| Orthogonal Frequency-Division Multiplexing(OFDM)technology plays an increasingly important role in various communication fields since it has lots of advantages such as high degree of freedom,high spectral efficiency,and strong resistance to multi-path fading.With the successful implementation of the "Belt and Road Initiative",the maritime wireless communication technology based on OFDM has attracted more and more attention.However,on the one hand,a complete channel modeling standard for maritime transmission environment has not been proposed at home and abroad,and the performance of OFDM technology in maritime channels is not yet clear.On the other hand,in maritime multipath channel,the time which data arrives at the receiver is different,which makes it difficult for the receiver to estimate the correct starting position of each frame,thereby causing timing estimation offset.Meanwhile,the relative motion between hulls and the mismatch of the sending and receiving crystals cause frequency offset.In order to ensure correct data demodulation at receiver,timing and frequency offset must be estimated and compensated.Based on the proposed maritime wireless channel model,this paper focuses on the in-depth research of timing and frequency synchronization technologies in OFDM system,including: 1)on the basis of the small-scale Physical Optics(PO)model,the influence of the wave height on the received signal and the Doppler effect caused by the relative motion between hulls are considered for the first time,and a dynamic multi-path channel model suitable for maritime wireless communication is proposed.Compared with the PO model,the proposed model more fully and truly reflects the actual communication channel characteristics at sea.2)aiming at the problem of timing synchronization in the maritime channel,based on the analysis of the performance of the classical timing offset estimation algorithm in the maritime channel environment,an improved training sequence structure based on Constant Amplitude Zero Auto Correlation(CAZAC)sequence is proposed.This sequence structure focuses on solving the problem that the original algorithm can't estimate the correct starting position when there is frequency offset in the system and the integer part of the frequency offset value is an odd number.Simulation results show that the proposed algorithm can accurately find the timing position compared with the original algorithm whether or not there is frequency offset in the system.3)aiming at the problem of frequency offset estimation in the maritime channel,based on the analysis of the performance of the classical frequency offset estimation algorithm in the maritime channel environment,a frequency offset estimation algorithm based on the Inter Carrier Interference(ICI)self-cancellation technique is proposed.Based on the Moose algorithm,this algorithm redesigns the pilot sequence and introduces self-cancellation technology at receiver to reduce the influence of ICI on the received signal,thereby improving the accuracy of frequency offset estimation.Simulation results show that in the dynamic multipath channel model at sea,compared with Moose algorithm,the proposed algorithm has a performance improvement of about 3dB.4)aiming at the maritime wireless communication environment,the overall design of receiver synchronization module for physical layer of OFDM system is proposed and FPGA implementation is completed.And a scheme for reducing hardware implementation complexity is proposed for the frame synchronization module.This scheme redefines the decision function such that each complex multiplication operation can eliminate two addition operations.The result shows that the proposed solution reduces the occupancy of the FPGA lookup table and register resources by 49.7% and 32.8%,respectively,compared to the original scheme. |
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