- 學位論文
節能次世代行動通訊系統之智慧不連續接收機制框架
Intelligent Discontinuous Reception Framework for Energy Efficient Beyond Fifth-Generation Mobile Communication Systems
摘要
不連續接收機制是最有效的使用者裝置之計時器基底省電機制。在長期演進技術（\ac{lte}）系統中，不連續接收機制的發展大幅度地延長了使用者裝置的電池壽命。當使用不連續接收機制時，使用者裝置被允許進入休眠狀態。按照被系統指定的不連續接收週期，該使用者裝置需要週期性的被喚醒，並檢查無線通道是否有傳送給該使用者裝置之下行資料。透過省略大部分的通道監測時間點，使用者裝置可以達到極高的休眠率。隨著無線行動網路演進到第五世代，使用者裝置之電池生命週期需求越發增加，以能支援多樣化的新興網路服務。第三代合作夥伴計劃（\ac{3gpp}）也不斷地改進不連續接收機制的設計，並在第十六版新空中介面（\ac{nr}）通訊標準當中加入了許多新的與不連續接收機制相關的功能。除了倒計時基底之設計，第三代合作夥伴計劃也提出了兩項控制信令基底之設計，分別是省電信令與使用者裝置輔助資訊機制。由此可知，在使用者裝置省電之議題上，第五世代、第六世代網路尚有許多待解決之問題。 許多學者在過去已經探討了不連續接收機制在各種不同應用情境下的表現，例如網頁瀏覽和異質網路。在他們的分析當中注重於使用者裝置的休眠率與封包延遲，並提出相應的理論分析模型。新的不連續接收機制亦是常常被各方討論以克服在特定狀況下的使用者裝置節能問題，特別是在第五世代新空中介面網路系統當中。波束成形技術被廣泛地應用在第五世代新空中介面系統當中來提升裝置接受信號功率，特別是在毫米波通訊的頻帶。此外，波束成形機制也仍然是被認為會在第六世代行動網路中扮演關鍵的演進推手。然而，波束成形機制也使得現有的省電機制，如呼叫機制，在設計上變得更加複雜，並對系統帶來了額外的控制信令傳輸的負擔。為了使通訊信號覆蓋所服務的區域，基站需要透過波束掃描的方式來完成廣播控制信令的傳輸。然而，波束掃描對於倒計時基底的省電機制而言是十分沒有效率的流程。頻帶分部機制是另一項新的技術被應用於第三代合作夥伴計劃新空中介面系統當中。透過配置頻帶分部的頻寬與彈性參數，它使基站能更彈性地運用無線通道資源。當使用者裝置使用了一個較小的頻帶分部時，它的功耗也會隨之降低，因為在該頻帶分部上，該使用者裝置僅需要監控較少的無線頻帶資源來接收下行資料。 在本論文中，我們主要目標在於提出智慧6G行動通訊系統之不連續接收機制框架，包含閒置模式不連續接收機制的波束基底之呼叫機制設計，以及連接模式不連續接收機制的頻帶分部切換機制設計。我們提出的波束基底之呼叫目標清單使基站能夠動態的呼叫使用者裝置。透過間接蒐集的使用者裝置資訊，基站可以在不透過波束掃描的方式，做出智慧化呼叫的決定，並同時減少呼叫機制的無線資源消耗，也最佳化整體系統使呼叫延遲降低。我們所提出之以馬可夫鍊為基底的理論分析模型結果已被驗證，與模擬之結果相符。分析結果顯示我們所提出的解決方案在呼叫成功率與系統容量的效能上勝過新空中介面的方法。而為了更了解使用者裝置在連接模式當中的功耗表現，我們也探討了頻帶分部基制與連接模式不連續接收機制的交互作用反應，並在此論文中針對此二機制提出智慧化的聯合設計。我們所提出的設計使這兩項技術能共同運作。我們的模擬結果也驗證了我們所提出的理論模型，並證明我們的方法在效能上優於現有的方法。
並列摘要
The Discontinuous Reception (DRX) is the most effective timer-based mechanism for User Equipment (UE) power saving. In Long Term Evolution (LTE) systems, the development of the DRX mechanism enormously extends the UE battery life. With the DRX mechanism, a UE is allowed to enter a dormant state. Given a DRX cycle, the UE needs to wake up periodically during the dormancy to check whether receive new downlink packets or not. The UE can achieve a high sleeping ratio by skipping most channel monitoring occasions. As the mobile network evolved to 5G, the battery life requirement increased to support various new services. 3rd Generation Partnership Project (3GPP) also enhances the DRX mechanism and adds new DRX-related features in the New Radio (NR) Release 16 standard. In addition to the time-based design, 3GPP proposed two signaling-based mechanisms, Power saving signal, and UE assistance information. Thus, there is still many issues for power-saving mechanism to solve in the 5G and beyond network. Researchers have investigated the DRX mechanism in various use cases, such as web browsing services and heterogeneous networks. They focus on the UE sleep ratio and packet delay and propose corresponding analytical models. New DRX architectures are also discussed to conquer the powersaving problem in specific schemes, especially in the 5G NR networks. The beamforming technique is applied in 5G NR systems to enhance the receiving signal power, especially for millimeter-wave communications. Moreover, the beamforming technique is still regarded as an essential solution to evolve the network to 6G. Beamforming complicates the power-saving procedure, such as paging procedure, and brings extra overhead to the transmission of control messages. In order to cover the serving area, the gNB should transmit broadcast control messages via beam sweeping. However, beam sweeping is inefficient for most timer-based power-saving operations. The Bandwidth Part (BWP) is another new technique applied in the 3GPP NR system. It enables the gNBs to utilize the wireless resource more flexibly by configuring the bandwidth and numerology for a BWP. When a UE uses a small BWP, its power consumption decreases because it monitors fewer wireless resources for downlink data. In this thesis, we target proposing intelligent Discontinuous Reception Framework for 6G mobile communication systems, including the beam-based paging design for Idle mode DRX (I-DRX) and the BWP switching design for Connected mode DRX (C-DRX). The proposed beam-based paging list enables the gNB to page UEs flexibly. With the implicit gathering of the UE information, the gNB can make intelligent paging decisions without beam sweeping, decrease the paging resources consumption, and optimize the system paging delay. The proposed Markov chain based analytical model is validated by the simulation results. The results show that the proposed schemes outperform the NR baseline in successful paging rate, delay, and system capacity. To further understand the UE’s power-saving performance in the connected mode, we also investigate the interaction of the BWP mechanism and C-DRX mechanism and proposed an intelligent joint design for the BWP and C-DRX mechanisms in this thesis. Our proposed design allows the BWP mechanism to collaborate with the C-DRX mechanism. The simulation results verify our analytical models and show that our mechanism outperforms the baselines.