蜂巢式無線網路中廣播群播系統之設計：資源管理、服務連續性及節能方法

Abstract

隨著近年通訊技術的發展，許多新穎的服務與應用逐一興起並為日常生活帶來諸多便利，然而巨量的服務也成為無線資源的重擔。為了緩解有限資源下傳輸巨量服務的壓力，廣播與群播技術成為未來無線通訊的熱門議題，透過廣播與群播技術，基地台可以用同一群無線資源將資料封包傳輸至使用者裝置，進而達到節省無線資源並提升資源使用效率的效果，另外，資源使用效率亦隨著接收廣播與群播服務的使用者裝置數量而顯著提升。本論文以提升次世代通訊的廣播與群播技術為目的，以新無線電技術中制定的廣播群播服務為基礎，本論文提出現有標準中可能面臨的問題，並從中選取三個設計方向做進一步詳細的研究及設計提升。

第一個設計方向為資源管理，對於廣域多細胞的網路布建場景，本研究提出透過將細胞網路劃分組成單頻網的方式以提升整體系統效能。本研究針對此議題制定一最佳化問題並設計圖論貪婪分割演算法尋找該最佳化問題的解答，透過模擬結果，本研究所提出之演算法可彈性適用於不同網路狀況並有效率地找到合適的細胞網路劃分配置。

第二個設計方向為服務連續性，本研究提出基於提示信息的服務連續性機制可以有效應用於廣播群播系統，且不需要於目標基地台額外保留無線資源，另外，透過與按需傳輸的系統資訊塊之概念結合，本研究進一步顯示若機制選擇及參數配置得宜，服務中斷時間之要求可以被滿足。因此，本研究提出一動態服務連續性框架，此框架可以彈性配置服務連續性機制以及相關參數，且模擬結果顯示此框架適用於不同網路狀況及不同服務需求狀況。

第三個設計方向為節電機制，基於目前新無線電技術下廣播群播服務的不連續接收標準，本研究指出該標準可能產生的缺失，進而造成節電效益下降。因此，本研究提出兩個可進行改善的方向，其一為對齊不連續接收的參數，透過最大化兩組不連續接收運作的重疊休眠時間達成較高的省電效益；其二為透過點對單點的傳輸，以避免額外的不連續接收運作造成多餘的啟動時間。基於以上兩個改善方向，本研究提出偏移及循環長度對齊之多群點對多點之機制，透過模擬顯示，本研究提出之機制有效且有效率的提升省電效益並確保延遲的需求。

於各研究議題中，本論文對於提出的機制、演算法、以及架構皆進行模擬驗證其效能以及其運作複雜度，驗證結果皆顯示本論文之各項議題中的設計皆可以有效率的在大量使用者裝置情境下運作並找出最佳或次佳解。另外，本論文亦針對各項研究議題，根據模擬結果提出觀察解釋以及未來可能可以進一步研究之方向。

總結而言，本論文針對新無線電技術中之廣播群播服務提出三個設計方向的改善方案：資源管理、服務連續性、以及節電技術。透過本論文提出的各項改善設計，可進一步提升廣播群播服務的效能，達到更高的效率、更能彈性處理各種網路狀況、以及更具擴展性。

Throughout the years, the burst of emerging fancy services and applications facilitates our daily life, while putting a heavy burden on radio resources. To address the overwhelming pressure on limited radio resources, multicast and broadcast technology is regarded as a promising solution. With multicast and broadcast technology, a base station delivers service packets to multiple user devices, which could reduce radio resource usage. The efficiency gain even increases as the number of user devices grows. In this dissertation, we aim at the enhancement of the next-generation multicast and broadcast technology. Taking New Radio (NR) Multicast and Broadcast Service (MBS) for example, we point out some problems that the current standardized mechanisms could confront. Among the enhancements, we select three design aspects for detailed research and enhancement.

The first design aspect is resource management. To enhance the system utility, we propose that a wide-area multi-cell topology is separated into multiple single frequency networks (SFN). We then form an optimization problem and propose a graph-based greedy partitioning algorithm (GGPA) as a solution. Simulation results show that GGPA flexibly adapts itself to different network conditions and efficiently finds a proper partitioning configuration.

The second design aspect is service continuity (SC). To avoid the additional reserved resource during the legacy handover procedure, we propose that a hint-based SC mechanism is adequate for the NR MBS system. Along with the concept of on-demand SIB, we further show that the interruption time requirement can be ensured if the SC mechanism and its parameters are finely chosen. As such, to flexibly and scalably configure the SC mechanism in NR MBS, we propose a dynamic SC configuration framework, whose performance superiority is validated by the simulation results.

The third design aspect is power saving. We point out the potential degradation of the power saving feature for the current NR MBS discontinuous reception (DRX) operation. Then, two enhancement directions are proposed. The first one is to align the DRX parameters for the extension of the dormant period, while the second one is to transmit the MBS packets through the point-to-point leg. Combining the two enhancement directions, we propose the offset and length aligned multi-group PTM (OLAM-PTM). The simulation results show that OLAM-PTM effectively and efficiently increases the power saving factor while guaranteeing the latency requirements.

With the proposed mechanisms, algorithms, and frameworks in the selected design aspects, we conduct simulations to verify their superiority over the baseline methods with low execution complexity. In the meanwhile, we also validate the scalability of the proposals. The proposed methods work efficiently and yield moderately acceptable performance even under a large number of devices, which is the case that exhaustive search is not feasible. Along with the simulation results, we provide observations and insights into each of the design aspects, as well as point out the potential future directions of multicast and broadcast technology.

To sum up, this dissertation addresses three design aspects in the NR MBS system: resource management, service continuity, and power saving. With the designs in this dissertation, the MBS system works in a more efficient, flexible, and scalable manner.