Research On OFDM Synchronization Based On Training Sequence In VDES

The concept of the VHF Data Exchange System(VDES)was originally proposed to solve the new signs of channel data link overload in the Automatic Identification System(AIS)of the ship,and to provide greater data exchange capability for the increasing sommunication requirements of E-navigation.VDES is a system connecting ships to ships,ships to shore,ships to satellites,etc.It has the potential to provide global coverage of communication,and has a very broad prospects in maritime applications such as improving ship communication congestion and safe navigation at sea.However,the limited bandwidth of wireless communication systems limit the development of potential applications.For VDES,it also faces the challenge of recieving more information in the allocated limited bandwith content.Therefore,Orthogonal Frequency Division Multiplexing(OFDM),one of the high-speed transmission technologies,is integrated into VDES to improve the system performance by increasing the data trann rate.As a potential transmission,OFDM can meet the needs of the system for high-speed data,and its multipath resistance can also effectively resist multipath effect.However,OFDM signals are particularly sensitive to synchronization errors.In order to improve the robustness of the system,this paper focuses on the research of OFDM synchronization technology based on training sequences in VDES.The research results are follows:(1)Discuss several typical symbol timing synchronization algorithms based on the training sequences to solve the symbol timing synchronization problem in OFDM synchronization technology.Include the following:S&C algorithm,Minn algorithm and Park algorithm.The theoretical derivation part of the algorithms are analyzed in detail,and the three algorithms are simulated experimentally respectively.And the simulation results show that the timing measurement curve of S&C alogorithm has a large platform,Minn alogorithm eliminates the peak platform and has a peak at the correct starting point of the symbol,Park alogorithm has a peak at the correct symbol timing,and the value at all other positions is very small.(2)Aiming at some problems of the synchronization algorithms,including the"platform" of the S&C algorithm,the curve peak value of the Minn algorithm is not sharp enough and has several side peaks,and the side peaks of the Park algorithm,etc.This paper proposes an improved synchronization algorithm based on training sequence.According to the conjugate characteristics of the time domain training sequence structure,and redefines the measurement function according to the structure of the new training sequence.Based on the proposed synchronization algorithm of the new training sequence,the timing measurement curve can generate a sharp peaks at the correct timing estimation points without the influence of side peaks,thus improving the accuracy of symbol timing.Moreover,compared with the classical algorithm,the improved algorithm proposed in this paper has a smaller mean square error.(3)Based on the improved algorithm with conjugate symmetric structure and VDES research background,through the analysis of the marine VHF data transmission system and simulation model,the high-speed transmission technology OFDM is integrated into VDES,and the physical layer of VDES is systematically analyzed by using digital modulation OFDM technology,and the performance of the communication system is simulated and analyzed.The simulation results show that this method can achieve lower bit error rate and effectively improve the marine VHF information transmission rate.