由於移動流量需求的增加，在非授權頻譜中部署 NR 是解決 Sub-6 GHz 授權頻譜頻寬不足之一種方法。然而，對於Ultra-reliable and low latency communication (URLLC) 服務的要求，非授權頻譜造成的不可靠之傳輸與無法預期之延遲是無法容忍的。本文專注於非授權頻譜。首先分析 Licensed Assisted Access (LAA) 與 WiFi 共存之問題，並提出一種提升網路效能之解決方案。然而，LAA 採用先聽後送 (Listen-Before-Talk，LBT) 之機制不適合應用於 URLLC，因為裝置於傳輸前可能經歷很長的等待時間。部署 URLLC 於非授權頻譜，利用全向天線之通道預留機制達成持續佔用非授權頻譜中之通道，從而確保隨時有閒置通道可以傳輸資料。然而，此方法有失公平性且於高干擾之環境下，通道預留成功率並不理想。因此，本文針對基於波束成型之多通道預留方法提出一個精準數學模型分析引入波束成型天線技術之通道預留成功機率及對 WiFi 之干擾。結合模擬與分析結果，顯示於高干擾環境下，特定之天線組合能讓通道預留成功率達到100% 並最小化對 WiFi 之影響。 此外，基於 frame based equipment (FBE) 機制，3GPP Release-17 提出用戶設備初始化通道佔用時間的方法，以增加非授權頻譜之通道利用率。然而，當 WiFi 流量增加時，URLLC可靠性將迅速降低。因此，本研究提出傳輸/接收切換方法與固定幀週期偏移調整方法以提高 FBE 可靠性。考慮到公平性，提出四種策略以平衡 URLLC 之可靠性與對 WiFi 之影響。模擬結果顯示，於高干擾環境中，與傳統 FBE 方法相比，URLLC 傳輸之可靠性顯著提高20%。 ;Due to the steady increase of mobile traffic demand, deploying the 5G New Radio (NR) in unlicensed spectrum is an intuitive approach to solve the bandwidth shortage problem in the Sub-6 GHz licensed spectrum. However, for the requirement of ultra-reliable and low latency communication (URLLC) service, the unreliable transmission and unpredictable delay caused by interference in the unlicensed spectrum are intolerant. This dissertation focuses on unlicensed spectrum. The coexistence problem between the Licensed Assisted Access (LAA) and the WiFi is analyzed firstly and then a solution to promote network performance is proposed. The Listen-Before-Talk (LBT) mechanism adopted by the LAA is not suitable for the URLLC service because the device may suffer a long waiting time before transmission. In literatures, the channel reservation approach with the omnidirectional antenna is a potential solution that continuously occupies channel(s) in the unlicensed spectrum to ensure URLLC transmission at any time. However, this approach is unfair, and in the high interference environment, the success channel reservation probability is unacceptable. Therefore, this dissertation considers the multiple channel reservation approach with beam-based antenna and proposes an analytical model to analyze the performance thoroughly. By introducing the fundamental beamforming antenna technology, the success channel reservation probability is indeed improved and the impact to the WiFi is also reduced. The results show that the success channel reservation probability can reach as high as 100% and the impact on the WiFi can be minimized by a specific antenna combination in high interference environment. In addition, based on the frame based equipment (FBE) scheme, the 3GPP Release-17 proposes a user equipment-initiated channel occupancy time to increase channel utilization in the unlicensed spectrum. However, the increase of WiFi traffic will degrade the URLLC reliability. Therefore, this dissertation proposes a transmit/receive switching scheme and a fixed frame period offset adjustment scheme to promote the FBE reliability. Considering fairness, four strategies are introduced to balance the FBE reliability and the impact on WiFi. The results show that compared with the legacy FBE, the URLLC reliability is significantly improved by 20% in the high interference environment.
