針對以中繼站輔助之LTE-A 網路所設計以服務品質為基礎之節能資源管理技術

Abstract

中繼站被設置於細胞邊界以增加活動於細胞邊界用戶端的通道品質。 與傳統的同質性網路相比，一旦基地台無法正確並及時完成繼站與基地台 之間的換手機制，系統效能將會被顯著降低。因而，在糟糕的通道環境下， 系統的能量消耗將會大幅增加。在現有的進階長期演進技術(3GPP Long Term Evolution Advanced, LTE-A) 標準中，用戶端必須依照固定周期回報 量測資訊給予基地台作為換手決策的依據，但此一固定周期有過長的可 能，使得基地台無法提供及時的換手決策。因此，具預測性換手機制在本 篇論文中被提出，用以增進基地台在現有的固定周期下進行更多換手決策 的可能性。依據部分可觀察馬可夫決策程序(Partially Observable Markov Decision Process, POMDP)，直接鏈結和中繼鏈結的通道品質可以被預測 出來。此外，本篇論文還針對具中繼站之LTE-A 系統中的資源管理問題 進行研究。在現有針對LTE-A 網路的研究中，許多會對能量效率造成影 響的要素並沒有被通盤考量。本篇論文提出一套名為合同式以服務品質 為基礎之節能性資源管理技術(Joint Energy-efficient QoS-based Resource Management, J-EERM) 的啟發式演算法。此套演算法用於通盤考量所有 傳送鏈結之分配管理多媒體廣播群播服務單頻網路(Multicast Broadcast Single Frequency Network, MBSFN) 子訊框、成對物理資源區塊(Physical Resource Block, PRB) 及傳送功率。此外，藉由本篇論文中所提出的具預 測性換手機制，許多在傳統換手程序中無法被獲得的資訊皆可被取得以使 用於J-EERM 演算法。本篇論文所提出的J-EERM 演算法其目的在於基 於服務品質及多重鏈結的考量下，達成良好的能量效率。由於J-EERM 演 算法的計算複雜度相當高，本篇論文還設計一套低複雜度的串聯式以服務 品質為基礎之節能性資源管理技術(C-EERM) 演算法，以增進其實用性。 研究結果顯示，本篇論文所提出的演算法皆能基於服務品質為基礎的前提 下為LTE-A 系統提供良好的能量效率。

Relay nodes (RN) have been suggested to be placed near the edge of a cellular network in order to improve link qualities of cell edge user equipments (UEs). Compared to conventional homogeneous networks, system performance for the relay-enhanced network can be significantly degraded if handovers between the RNs and evolved node base-station (eNB) are not correctly and immediately determined by the eNB. Therefore, the UEs may suffer from worse channel conditions which can result in increased energy consumption of entire network. In existing long term evolution advanced (LTEA) standard, fixed reporting time period from the UEs to eNB is considered inflexible which can be too long to provide immediate handover decisions. Hence, prediction-based handover (PH) process is proposed to allow eNBs to make potential handover decisions within the UE’s reporting period. The channel qualities for both the direct and relay-enhanced links during this period are predicted based on the partially observable Markov decision process (POMDP). Furthermore, this thesis also investigates the resource management problem in the relay-enhanced LTE-A systems. Existing research work does not fully consider all the influential factors to achieve energy efficiency for the LTE-A networks. In this thesis, a heuristic scheme named joint energy-efficient QoS-based resource management (J-EERM) is proposed to allocate multicast broadcast single frequency network (MBSFN) subframes, physical resource block (PRB) pairs, and transmission power with all combinations of transmission link. Moreover, some of the information needed in J-EERM scheme which can not be acquirable under conventional handover process can be obtained under proposed PH process. The proposed J-EERM scheme is targeting at energy efficiency with the consideration of both quality of service (QoS) requirements of UE and direct/two-hop communications. Moreover, the cascaded EERM (C-EERM) scheme is designed to reduce computational complexity compared to J-EERM scheme. Numerical results show that the proposed schemes can provide energy efficiency with consideration of UE’s QoS requirements for the LTE-A systems.