Research On OFDM Synchronization And Channel Estimation For Vehicular Communication

The development of future fifth-generation(5G)technology will bring new opportunities and challenges to the vehicular communication technology.Due to each node in the vehicular cooperative communication network which based on OFDM technology has respective oscillators,there are many timing offset and carrier frequency offset,which bring new synchronization problem for the vehicular cooperative communication systems.In addition,the traditional channel estimation algorithm is affected by the vehicular communication,which is characterized by high speed and complex channel environment.It is needed to study the channel estimation algorithm which is suitable for the vehicular channel to ensure the correct recovery of the received signal.This paper focuses on the research of synchronization and channel estimation technology of vehicular communication OFDM system.The main works are shown as follows:1.In view of the previous synchronization algorithms,there are some problems of timing ambiguity and high interference peak.A novel preamble structure based on weighted CAZAC sequence is designed to solve symbol timing and carrier frequency synchronization of OFDM system.The conjugate symmetry of training sequence is used for symbol timing and frequency offset estimation.Firstly,the delay and symmetry correlation characteristics of the training sequence are used to estimate the symbol timing and coarse frequency offset.Then with the redundancy of the cyclic prefix,the fine fractional frequency offset is completed.Finally,the cyclic shifting operation in time domain is adopted to estimate the integer frequency offset.The effects of symbol timing and carrier frequency offset on OFDM system are analyzed.The symbol timing synchronization and carrier frequency offset estimation algorithm which based on the training symbol are studied,and the theoretical analysis and performance simulation are carried out.By comparing with other algorithms,it can be concluded that the new algorithm can obtain high timing accuracy and frequency offset estimation accuracy in multipath time varying channel.2.In this paper,the impact of the mobile environment on the OFDM system is analyzed,and the BEM is studied in the presence of residual carrier frequency offset.Based on the maximum likelihood estimation method,a carrier frequency offset and channel estimation algorithm based on BEM is improved.As the comb pilot in the mobile environment will be affected by the interference from the data carrier,the comb shaped pilot cluster is used to reduce the ICI in the pilot position.The proposed algorithm can effectively reduce the number of estimated parameters in the vehicular time-varying channel,and the simulation results show that the BER performance of the proposed algorithm is better than that of the channel estimation algorithm without considering the carrier frequency offset estimation.