The Research Of OFDM Channel Estimation Technology In The Vehicular Environments

In recent years,how to realize reliable communication in Vehicle-to-Vehiclue environments is becoming a research focus with the development of vehicular communication and the standardization of IEEE 802.11 p.As a key technology,channel estimation is a technical difficulty in the vehicular environments,because it is also closely related to the key techniques of wireless communication,such as equalization and diversity receiving.Hence,it is significant to study the technology of channel estimation.IEEE 802.11 p using OFDM as its key technology is the main standard of Internet of Vehicles at present and this paper focuses on the techniques of OFDM channel estimation in the vehicular environments.The main work of this paper are the following aspects:(1)Theoretical basis of the OFDM channel estimation technology in the vehicular environments are discussed firstly.Based on the architecture of the vehicle networking systems and the main parameters of the IEEE 802.11 p standard,the characteristics of the vehicular channel are analyzed from the three aspects of the channel impulse response in the vehicular environments,the time-frequency doubly characteristics and the sparsity of the delay doppler domain.Two kinds of the vehicular channel simulation models in this thesis: the Jakes model and the extended ITU channel model are introduced.(2)Build the system model of the OFDM channel estimation based on pilots;the performance based on typical pilots are analyzed and simulated and the influence of the pilot structure on the performance is illustrated.Based on the analysis of typical pilot structure,a new improved pilot structure for channel estimation is proposed and the channel estimation performance of the improved pilot structure and the comb like and diamond pilot structure are compared and analyzed.The numerical simulations indicates that the improved pilot structures proposed by this paper is better than the comb pilot structure and diamond pilot structures.(3)In the view of the time and frequence doubly selective channel in the vehicular environments,the characteristics of compressed sensing(CS)is combined.Based on the the channel sparsity of the delay doppler domain in the vehicular environments,the OFDM channel estimation problem in the vehicular environments can be converted into a standard compressed sensing reconstruction model and the channel estimation can be realized by the OMP(Orthogonal Matching Pursuit)reconstruction algorithm in the compressed sensing algorithms.On this basis,an improved OFDM channel estimation in the vehicular environments based on the compressed sensing is proposed by exploiting the correlation in the adjacent channel symbol.The method can reduce the sparsity degree of the signal processing and reduce the complexity of the iterated operations in the compressed sensing algorithms.The simulation results show that the improved OFDM channel estimation method based on the compressed sensing is better than the channel estimation method based on the OMP in compressed sensing and based on the pilots.