這篇論文探討了在低軌衛星(low earth orbit)通信系統中採用H_∞濾波器進行頻率偏移估測。由於移動終端和衛星之間的相對速度較高，低地球軌道衛星通信信號會遭受嚴重的多普勒頻移。本論文提出一種，基於正交分頻多工(OFDM)的LEO衛星傳輸調適性通訊演算法，以改善多普勒頻偏，本論文使用H_∞濾波器，並結合地理空間位置(衛星運行軌道及地面基站位置)利用圓形軌道LEO衛星的可預測多普勒特徵，提出新型的通訊演算法。藉由所提出的演算法的估計，可以隨衛星位置的移動，持續進行載波頻率偏移(CFO)的估計值更新，藉此可降低系統複雜度，並執行載波間干擾消除，更進一步提高帶寬效率，以達到改善衛星通訊嚴重的多普勒偏移之問題，進而使低地球軌道衛星衛星傳輸可以更有效利用。

This paper discusses the use of H_∞filters for frequency offset estimation in LEO (low earth orbit) satellite systems. Due to the high relative speed between the mobile terminal and the satellite, the LEO satellite communication signal will suffer severe Doppler shift. This paper proposes an adaptive communication algorithm based on OFDM-based LEO satellite transmission to improve the Doppler frequency offset. This paper refers to the H_∞ filter combined with geographic space location (satellite orbit and ground base station location), and using the predictable Doppler characteristics of LEO satellites in circular orbits to propose an adaptive communication algorithm based on OFDM for LEO satellite transmission to improve Doppler frequency offset. With the estimation of the proposed algorithm, the estimated value of CFO (carrier frequency offset) can be continuously updated with the movement of the satellite position. This can reduce system complexity, perform inter-carrier interference cancellation, and further improve bandwidth efficiency, so as to improve the serious Doppler shift problem of satellite communication, and thereby enable the LEO satellite transmission of OFDM to be more effectively used.

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