中繼站輔助細胞網路之系統設計與最佳化

Abstract

下一世代行動通訊系統中，中繼站輔助細胞網路架構被視為一可行且具有潛力的網路架構。此架構佈放中繼站在傳統蜂巢式網路中，以多躍方式協助基地台與使用者之間的訊號傳輸。它提供一個以較低成本之佈建方式來改善細胞覆蓋，提昇使用者傳輸速率，提高細胞系統容量，以及減少使用者的上行傳輸功率。 發展中繼站輔助細胞網路之重要關鍵即是需從理論與實務等方面進行系統效能之全面性評估。本論文考慮在一般的系統配置下，探索中繼站輔助細胞網路之系統設計與優化。文中主要分為三大部份進行探討： 在第一部分研究中，我們針對中繼站輔助細胞系統在多細胞環境下之下行性能進行研究。綜合考量影響系統效能之系統參數：中繼站之佈放位置、使用者之路徑選擇、頻譜資源重用、資源配置等，以及考慮兩種使用者體驗品質，即固定頻寬分配與固定傳輸速率分配，我們提出以基因演算法為基礎之演算法進行中繼站輔助細胞網路之系統效能之優化。實驗結果顯示，相較於傳統網路架構，中繼站輔助細胞網路之下行細胞容量以及使用者之傳輸速率大大地被提昇。 在論文的第二部分，我們提出中繼站輔助細胞之上行效能之設計與最佳化。在上行效能中，使用者平均傳輸功率消耗以及上行系統的頻譜利用效率是兩個重要的效能指標。文中考慮中繼站的佈放位置、頻率重用模式、使用者之路徑選擇以及資源分配等系統參數進行系統設計。利用基因演算法搭配一個多重存取干擾估算演算法對中繼站輔助細胞系統進行效能之優化。實驗結果表明，中繼站輔助細胞網路之上行細胞容量獲得提昇，以及使用者之上行傳輸功率消耗獲得改善。 在第三部分研究中，我們考慮在似曼哈頓式環境中，多跳躍式中繼網路的傳輸排程問題。利用似曼哈頓式環境中的高遮蔽效應，搭配在基地台與中繼站之指向性天線，文中提出有效率之傳輸排程方法以提昇此環境下之細胞系統容量。實驗結果指出，在似曼哈頓式環境中，基地台與中繼站搭配指向性天線，可有效提升系統頻譜效能。 本論文從理論與實務兩方面，針對中繼站輔助細胞網路進行研究。我們考慮在不同的系統配置下，中繼站輔助細胞網路之上行與下行之設計優化與理論效能。我們亦考量在似曼哈頓環境中，中繼站輔助細胞網路之實際的傳輸排程問題。綜合實驗結果說明，中繼站輔助細胞網路可提昇使用者傳輸速率，提高細胞系統容量，以及減少使用者的上行傳輸功率，並且提供似曼哈頓環境中較好的細胞覆蓋。

Deploying fixed relay stations (RSs) in traditional mobile cellular networks is widely recognized as a promising technology in next generation mobile communication systems to improve cell coverage, user throughput and system capacity, to save transmit power of a mobile station (MS) in the uplink, and to provide a low cost deployment for coverage extension. One crucial step toward developing such a relay-assisted cellular network is to fully evaluate its performance from both theoretical and practical points of view. In this dissertation, we aim to explore the system design and the optimization of relay-assisted cellular networks in multi-cell environment by considering general system configurations. In the first part of this dissertation, we aim to investigate the downlink performance limits of a general relay-assisted network with optimized system parameters in a multi-cell environment. Two types of quality of end-user experience (QoE), i.e., fixed bandwidth allocation and fixed throughput allocation, along with two path selection methods, i.e., spectral-efficiency based and signal-to-noise-plus-interference ratio based are investigated. A genetic algorithm (GA) based method is proposed for joint optimization of system parameters, including the number of RSs and their locations, frequency reuse pattern, path selection and resource allocation so as to maximize the system spectral efficiency. Numerical results show that significant improvement on the system spectral efficiency and the user throughput are achieved in the relay-assisted cellular network. In the second part, the aim is to study the uplink performance of a relay-assisted cellular network. Two performance measures, average power consumption of mobile stations and uplink system spectral efficiency, are optimized by jointly considering the system parameters of RSs’ locations, reuse patterns, path selections and resource allocation. GA-based method along with a method of MAI (multiple access interference) estimation is applied to solve the optimization problem. Numerical results show that with proper deployment of RSs both power consumption of MSs and the system capacity are remarkably improved in the uplink. In the third part, we investigate the important issue of resource scheduling for multi-hop relay networks in the Manhattan-like environment. New resource scheduling methods are proposed for the multi-hop relay network with directional antennas equipped at both the base station and relay stations. By taking advantage of the effect of high degree shadowing in the Manhattan-like environment, the system throughput can be largely increased by the proposed methods as compared to the system with omni-directional antennas. In this dissertation, the theoretical performance in both downlink and uplink with general configurations in relay-assisted cellular networks is presented. The practical issues of resource scheduling of relay-assisted cellular networks in the Manhattan-like environment is also addressed. With comprehensively evaluations, we can conclude that a relay-assisted cellular system is with the benefits to improve the system capacity and the user throughput, to save transmit power of an MS in the uplink, and to provide better coverage in the Manhattan-like environment with the optimized system parameters.