由於成本及地理環境等多項挑戰，單純依賴陸地網路(TN)難以實現全球性覆蓋。因此，3GPP提出以衛星通訊系統做為TN的補充，為TN服務能力不足的區域提供可靠的互聯網接入服務。然而，衛星與移動終端之間的相對速度較高，所以衛星通訊訊號會遭受嚴重的都普勒偏移，且延遲估計容易受到都普勒偏移影響。因此本篇論文提出了低軌衛星(Low Earth Orbit)通訊系統中，基於Zadoff-Chu序列所設計的延遲與載波頻率偏移估測方法。本方法是利用接收訊號與Zadoff-Chu序列進行相關性運算所得到的峰值，進一步進行延遲及都普勒偏移的估計。 模擬結果表明，本文提出的估測方法能夠在都普勒偏移大的低軌衛星通訊系統中達到良好的表現，能夠在較低的訊雜比就達到1%的漏檢率(Missed Detection Rate)，且在滿足1%漏檢率的狀況下，達到較低的定時提前及都普勒偏移估計的均方誤差(Mean Square Error)。 ;Due to various challenges such as cost and geographical environments, it is difficult to only rely on terrestrial networks (TN) to achieve global coverage. Therefore, 3GPP proposed the utilization of satellite communication systems to support TN, and provide reliable internet access services in areas where TN coverage is unavailable. However, there are significant Doppler shifts in the Low Earth orbit (LEO) satellite communication systems due to their high relative velocities with user equipment and base station. The Doppler shifts also influence the delay estimation. Consequently, to overcome this problem, this study presents a delay and carrier frequency offset estimation method designed for LEO satellite communication systems by utilizing Zadoff-Chu sequence. This method leverages the correlation between the received signal and Zadoff-Chu sequence to estimate delay and Doppler shifts. The simulation results show the effectiveness of the proposed estimation algorithm performs in LEO satellite communication systems with significant Doppler shifts. It can achieve 1% missed detection rate at relatively low Signal-to-Noise Ratio. Furthermore, it exhibits lower mean square error in delay and Doppler offset estimation while 1% missed detection rate.
