| 摘要: | ITU-R將第五代行動通訊技術（5G）正式命名為IMT-2020。5G具備三大應用場景，分別為增強型行動寬頻服務 （enhanced mobile broadband，eMBB）、巨量多機器型態通訊 （massive machine type communications，mMTC）與超高可靠度和超低延遲通訊（ultra-reliable and low latency communications，URLLC）。為實現前述三大應用場景，ITU定義IMT-2020共有八大關鍵需求指標，如峰值數據速率、移動性、頻譜使用效率、區域傳輸流量等等。不同應用場景之關鍵需求指標各有差異，因應指標特性，可找出適合之頻譜資源。其中URLLC主要特色為高可靠度及低延遲，應用於特殊環境（如工廠自動化、自動駕駛等）。現今主流探討實現 URLLC 服務是以授權頻譜為主。因授權頻譜價格高昂，且商業應用發展下的需求日益增加，使用非授權頻譜（unlicensed band，UB）有望成為較小規模工廠導入物聯網的解決方案。故本研究目標為實現URLLC於UB之技術。
我們先前的研究分別提出非授權頻譜之單通道預留機制與多通道預留機制，透過通道偵測以及動態跳頻的方式以確保任何時間有通道可以做即時傳輸。由於先前機制中，基地台（gNB）及使用者設備（user equipment，UE）需要在同一個時間點偵測一個或多個通道，偵測到空閒通道才可成功預留通道，成功率較不理想。後續研究延續先前的機制進行改良，提出了漸進式單通道預約機制（progressive single channel reservation，P-SCR）。P-SCR改良通道預約機制，使gNB先選擇一個空閒通道，並且給定所有UE一段時間進行通道偵測及占用。此方法除了可大幅提高通道預留的成功率，能適應更複雜的通道狀況，且最多僅同時占用兩個通道，提高頻譜使用效率、降低對異質系統的影響，以達成URLLC嚴苛的標準。本研究將針對P-SCR機制做理論分析，以數學分析節點間之關係，證明P-SCR確實可以提高通道預約的成功率。並且根據分析結果提出分群的機制。模擬結果證明透過分群機制確實能降低外圈UE執行通道預約所需之時槽數，並提高通道預約之成功率。
;ITU-R officially specifies the fifth generation mobile communication technology (5G) as IMT-2020. 5G has three application scenarios, namely enhanced mobile broadband (eMBB), massive machine type communications (mMTC), ultra-high reliability and low latency communications (URLLC). In order to achieve the above three application scenarios, the IMT-2020 has defined several key requirements, such as peak data rate, mobility, spectrum efficiency, regional transmission traffic, etc. The key requirements of different application scenarios are quite different. According to the characteristics of requirements, the suitable spectrum resources can be identified. The main features of URLLC are high reliability and low delay, which are used in special environments (such as factory automation, automatic driving, etc.). Nowadays, the mainstream discussion on the implementation of URLLC services is based on the authorized spectrum. Due to the high price of licensed spectrum and the increasing demand under the development of commercial applications, the use of unlicensed band (UB) is expected to become a solution for small-scale factories to implement the Industrial Internet of Things. Therefore, the goal of this research is to realize the technology of URLLC over UB.
In our previous research, we proposed the single channel reservation mechanism and the multi-channel reservation mechanism to ensure that there is a channel reserved for real-time transmission at any time through channel detection and dynamic frequency hopping. With such mechanisms, the base station (gNB) and user equipment (UE) need to detect one or more idle channels at the same time to successfully reserve the channel(s). Our subsequent research proposed a progressive single channel reservation (P-SCR) in order to further improve the ability of channel reservation. The P-SCR lets gNB first select an idle channel, and then informs all UEs to detect and occupy that channel within a period of time. P-SCR mechanism can greatly improve the success probability of channel reservation and occupy only two channels at most at any time. It indeed improves the spectrum utilization efficiency, reduces the impact on heterogeneous systems, and satisfies the URLLC requirement. In this thesis, we analyze the P-SCR mechanism through mathematical analysis. We analyze the relationship between a pair of nodes to prove that P-SCR can indeed improve the success probability of channel reservation. According to the analysis results, we further propose two grouping methods. Simulation results show that, for the outer UE, the grouping methods can indeed reduce the required time slots for reservation meanwhile improving the success probability of channel reservation. |
