Research On Doppler Frequency Offset Estimation For OFDM Systems In High Speed Environment

Nowadays, high-speed rail communication and aeronautical communication are leading the mobile communication into a high-speed era. At high speed, the communication environment will become more and more complicated. The influence of Doppler shift caused by the relative motion between the transmitter and the receiver More and more significant.However, the orthogonality of OFDM systems is seriously influenced by the frequency offset, so the OFDM system is prone to interfere with each other in the high dynamic environment. Affect the communication quality of the communication link. Therefore, it is urgent to study the Doppler frequency estimation technique in OFDM system under high-speed environment, accurately estimate the Doppler shift caused by high-speed environment, compensate in time, reduce the error rate and improve the communication quality.The content of this thesis is mainly based on the following two parts:1) A novel algorithm for Doppler frequency estimation of OFDM systems in high speed mobile environment is proposed and analyzed. The algorithm achieves Doppler frequency offset and Doppler rate of variation by the joint maximum likelihood estimation of the non-adjacent preamble pattern by means of the time-domain repetition preamble sequence. By comparing the performance of the proposed algorithm, the accuracy of the proposed algorithm is improved from 10-3 to 10-6, and the estimation performance is improved obviously. 2) This thesis presents a Doppler frequency estimation algorithm based on the spontaneous self-receiving of a MIMO system with millimeter-wave in a high dynamic environment. The multiple-antenna transmitter transmits the diversity waveform synchronously by using the multiple-antenna of the transmitting antenna,and receives the echo signal at the receiving end, and then collects the received signal to obtain the Doppler frequency offset and the relative position angle. The accuracy of the proposed algorithm is improved from 10-3 to 10-5, and the performance of the algorithm is improved obviously.Through the research of this subject, the two algorithms proposed in this thesis can meet the demand of Doppler frequency estimation in high-speed mobile environment and restore the Doppler effect problem in high-speed mobile environment better, so as to guarantee the communication quality for the high-speed mobile environment.