為滿足全球覆蓋的網路需求，衛星──地面整合網路 (satellite-terrestrial integrated networks) 被視為是一個具有前景的作法。此場景下，相對較低延遲的低軌道(low-earth orbit, LEO)衛星星座扮演相當 重要的角色。低軌衛星覆蓋範圍大、移動速度快等特性，會產生延遲不確定性、都卜勒偏移，對隨機接入(random access, RA)前導訊號(preamble)的傳輸造成影響，導致難以成功偵測前導訊號或無法取得前導訊號正確的時間延遲。在本文中，我們提出一個新的前導訊號 DRMS(double root merging sequence, DRMS)，並推導在不同載波頻率偏移(carrier frequency offset, CFO)、子載波間距 (subcarrier spacing, SCS)、訊號長度下，相關性峰值的位移量。基於推導結果，我們設計出相對應的前導訊號偵測方法。模擬結果說明 DRMS 能夠消除時頻偏移的影響，並且能在大幅載波頻率偏移下維持前導訊號偵測的效果。;The promising satellite-terrestrial integrated network has been considered to meet the network requirement of global coverage. Low earth orbit (LEO) constellations with respective low latency take a large part in this scenario. The characteristics of broad coverage, fast-moving speed results in delay uncertainty and Doppler shift to random access (RA) preamble, which will lead to poor time estimation and preamble detection rate. In this paper, we proposed a double-root RA preamble sequence, DRMS, which concatenating K ZC sequences with the same root index while superposing another root ZC sequence. We derived peak offsets caused by Doppler shift by carrier frequency offset (CFO), subcarrier space (SCS), and concatenation number K. Based on the derived peak offset, we designed a preamble detection scheme for DRMS. The simulation result shows that the DRMS can mitigate the impact of timing/frequency offset and maintains the preamble detection performance even under a large CFO.
