具多重服務特性之分碼多工階層式細胞系統的基地台選取機制之研究

Abstract

在第三代行動無線通訊系統中，分碼多工( Code Division Multiple Access CDMA )因其抗干擾與高頻譜利用率的特性，成為最具有潛力的無線寬頻通訊技術[1]-[3]。由於CDMA允許多人同時傳輸，在提供多樣化服務的需求下，頻譜資源管理(Radio Resource Management, RRM)成為不可或缺的重要課題。本篇論文的目的在探討具多重服務之分碼多工階層式細胞系統的基地台選取機制。 下一代行動無線通訊系統中，數據服務包含WWW、E-mail、或影像等變成一個主要的服務種類，而其要求較高的頻寬及多樣化服務種類的品質保證要求(QoS)。因此，很難找出一個適合的共用訊務模型來近似各種不同的數據資料。本文想要比較二種大家常用的數據訊務模型，改良型的on-off數據訊務模型和Pareto based的數據訊務模型，進而探討二個不同訊務模型對於系統的影響。 第二，hotspot微細胞(micro cell)通常發生在系統中有某小區域存在較高的負載。雖然用hotspot微細胞台，可以增加系統整体容量和效能，可是由於大細胞和微細胞使用相同的頻帶，使得二個基地台之間會互相干擾。在本文中，我們將研究不同的階層式細胞系統之基地台選取機制，使得階層式細胞系統可以有效的增加容量而不會使得相互間的干擾太過嚴重造成系統效能下降。我們提出一個新的相對pilot訊號強度選取機制。它透過一個保護性質的門檻，使得此機制不只可以保證微細胞能有效的分享hotspot地區的數據負載給大細胞伺服，而且還可以避免微細胞因太過擁擠而達到容量上限，使得hotspot微細胞中的使用者被拒絕。我們將證明我們所提出的機制在階層式細胞系統下可以比大部份的基地台選取機要來得好。

CDMA is one of the most potential techniques in the third generation mobile communication system because of its resistance of interference and high frequency efficiency. Because the CDMA system can serve many users with various services requirements at the same time, radio resource management (RRM) becomes a very important issue. The goal of this thesis is to study cell site selection technique for hierarchical CDMA networks with multi class traffic. Data services, such as WWW, E-mail and video, etc, will become primary services in the next generation mobile wireless communication system. Theses services require higher bandwidth and diverse QoS requirements. Thus, it is difficult to find a common traffic model that can approximate all kinds of data traffic. This thesis will compare two data traffic models, i.e. a modified on-off data traffic model and Pareto based data traffic model, and evaluate their impacts on the system performance of cellular network. Secondly, hotspot micro cells often occur in a small area requesting high traffic load. Employing hotspot micro cells can increase system capacity and improve system performance. Because a micro cell and a macro cell use the same frequency band, the system may suffer interference with each other. In this thesis, we investigate different cell site selection algorithms for hierarchical cellular systems to ensure that the system can effectively improve system capacity without suffering severe interference with each other. For this purpose, we propose a new relative pilot based cell site selection algorithm. Through assigning a protection threshold, the relative pilot based cell site algorithm not only can ensure a micro cell to effectively relieve hotspot data traffic load, but avoid the micro cell from serving too much traffic beyond its capability. We will demonstrate that the proposed relative pilot based cell site selection algorithm outperforms most current site selection algorithms in hierarchical CDMA cellular system with multiple traffic classes.