在 5G 非地面網路 (NTN) 中，隨機接入使用的前導碼在低地球軌道(LEO) 衛星環境中會受到長時間延遲和高都卜勒頻移的影響。3GPP 提出在用戶設備 (UE) 端進行時間和頻率的預補償。衛星將其位置和速度以星曆格式廣播給用戶設備 (UE)，用戶設備使用全球導航衛星系統(GNSS) 接收器來確定其位置。因此，UE 可以在接入衛星網路之前進行時間延遲和頻率偏移的預補償。儘管有預補償的幫助，前導碼設計仍然會遭受時序提前 (TA) 估計錯誤。在本論文中，我們提出了一種非等差循環移位前導碼設計來減少這些錯誤。數值評估表明，與等差循環移位設計相比，我們提出的方案在首次接入成功率和 TA 估計錯誤率方面具有更高的性能。;In 5G Non-terrestrial networks (NTN), preamble adopted in random access suffers from the long delays and high Doppler shifts in Low Earth Orbit (LEO) satellite environments. 3GPP proposes time and frequency pre-compensation at user equipment (UE) side. Satellites broadcast their position and velocity in ephemeris format to the UE, which uses Global Navigation Satellite System (GNSS) receiver to determine its position. Hence, UEs can pre-compensate time delays and frequency shifts before accessing the satellite network. By the aid of pre-compensation, preamble design still suffers from timing advance (TA) estimation errors. In this thesis, we propose a non-common-difference cyclic shift preamble design to reduce these errors. Numerical evaluations demonstrate that our proposed scheme preforms a higher first access success rate and lower TA estimation errors compared to non-common-difference cyclic shift designs.
