Research On Ka-band Satellite Communication System’s Doppler Shift Estimation Based On OFDM Technology

Ka(K-above)band is a part of the electromagnetic spectrum’s microwave band.The range of its frequency is26.5to40GHz. It refers to the frequency above K band.The broad band is one of its important characteristics; its available bandwidth is up to3500MHz. Because of this characteristic, it can be used into satellite communication toincrease the capacity of the communication; it can also implement a narrow beam toobtain a high EIRP (Effective Isotropic Radiated Power). At meanwhile, the high speedbetween the user terminals and the satellites can lead to the Doppler Effect. Faster theuser terminal moves, stronger the Doppler effect is. It is hard for the demodulation atthe receiving end. So the estimation and analysis of the Doppler shift is an effectiveway to improve the quality of communication and ensure the quality of communicationreliability.OFDM (Orthogonal Frequency Division Multiplexing) is a multicarriermodulation technique. High frequency spectrum utilization is the biggest advantage ofthis technique, and it can also resist to multipath fading. OFDM technology hasbecome the key technology of high speed data transmission. The combination ofOFDM technology and the satellite mobile communication system can not onlyimprove the utilization of satellite system resources but also be in favor of thecombination of satellite system and the ground wireless/mobile communicationnetwork. But the mean disadvantage of OFDM technology is its sensitive to theDoppler frequency shift, especially in high speed environment, which leads to thedestruction of the orthogonality between subcarriers, produce serious inter carrierinterference (ICI). For this reason, I want to make a deep research of the Dopplerfrequency shift estimation in satellite mobile communication system in my paper toimprove the performance of the system.At the beginning of my paper, I have researched the impact of the Dopplerfrequency shift to the satellite mobile communication system based on the OFDM technology, focusing on the Doppler frequency shift estimation algorithm. I studied theDoppler frequency offset algorithm based on cyclic prefix. Then I introduced anestimation algorithm of Doppler frequency shift based on the transform domain,inserting pilot symbols into the OFDM symbols, analyzed the signal’s pilot frequencyspectrum in transform domain received to obtain the information of Doppler frequencyshift; At last I made a study of the Doppler frequency in a way of approximatemaximum likelihood estimation algorithm. Through the simulation analysis, the rangeof the Doppler frequency estimated of this algorithm is inversely proportional to thebiggest correlation length it used. In the last part of this paper, I tried to combine theMIMO (Multiple-Input Multiple-Output) technique with the satellite communicationsystem based on Ka band, analyzing the Doppler frequency shift of the satellitecommunication system based on the MIMO OFDM technology in the way of precisemaximum likelihood estimation algorithm. Then I came to a conclusion of theestimation to the Doppler frequency shift and the characteristic of the system’s bit errorrate after making compensation to it. The Ka band satellite system based on MIMOOFDM technology is also sensitive to the Doppler frequency shift.