| 摘要: | 窄頻物聯網(narrowband Internet of Things, NB-IoT)是第三代合作夥伴計畫(the third generation partnership project, 3GPP)所制定一個新的物理層，目的是支持大量物聯網用戶設備 (user equipment, UE)應用在大規模機器類型通訊 (massive machine-type communication, mMTC)。為了進一步擴展覆蓋範圍和提高UE連接數量，非地面網路(nonterrestrial networks, NTN)中的衛星通訊成為最有潛力的解決方法。然而，NB-IoT系統最初是為地面網路(terrestrial networks, TN)設計的，當引入至NTN時，現有的運作方式需要進行一些修改，使其能夠容忍衛星通訊帶來的高頻率偏移及傳播延遲，並確保NTN與TN之間的兼容性。其中一個挑戰是隨機接入(random access, RA)程序，RA程序涉及前導碼檢測和上行鏈路同步，由於頻率偏移及傳播延遲較大，傳統為TN設計的方法無法提供準確的檢測及估計。因此，本文設計一個無需全球導航衛星系統(global navigation satellite system, GNSS)的系統來進行RA，透過在衛星上的窄頻物理層隨機接入通道(narrowband physical random access channel, NPRACH)接收機進行都卜勒頻率的預補償與後補償以克服嚴重的都卜勒效應，而定時提前(time advance, TA)與隨機接入機會(random access opportunity, RAO)推延可以克服訊號高傳播延遲。NPRACH前導碼(preamble)採用基於奈曼-皮爾森準則(Neyman-Pearson criterion)來檢測符元(symbol)平均功率，同時提出可以估計大範圍載波頻率偏移(carrier frequency offset, CFO)與時序誤差(timing error, TE)的方法。最後在模擬中分析漏檢機率(miss detection probability)與估計的均方誤差(mean-square error, MSE)，結果表明上述提及的方法能夠應對衛星帶來的通道損害。;Narrowband Internet of Things (NB-IoT) is a new physical layer standard established by the third generation partnership project (3GPP). It is designed to support a large number of Internet of Things (IoT) user equipment (UE) in massive machine-type communication (mMTC) scenarios. To further extend coverage and massive connectivity, satellite communication within nonterrestrial networks (NTN) has emerged as a promising solution. However, the NB-IoT system was initially designed for terrestrial networks (TN), and when introduced to NTN, the existing operations need to be modified to tolerate the high frequency offset and propagation delay introduced by satellite communications, ensuring compatibility between NTN and TN.
One of the challenges is the random access (RA) procedure, which involves preamble detection and uplink synchronization. Due to larger frequency offsets and propagation delays, conventional methods designed for TN cannot provide accurate detection and estimation. Therefore, this thesis designs a global navigation satellite system (GNSS)-free system for RA, overcoming severe Doppler effects through pre-compensation and post-compensation of Doppler frequency at the receiver of the narrowband physical random access channel (NPRACH) on the satellite. Problems caused by long propagation delays are also addressed. Furthermore. This thesis employs symbol average power detection based on the Neyman-Pearson criterion and proposes a method to estimate a wide range of carrier frequency offset (CFO) and timing error (TE). Finally, simulations are conducted to verify the miss detection probability and mean-square error (MSE) of the estimation, showing that the proposed method can handle the channel impairments introduced in the NTNs. |
