一個降低Femtocell網路通話路由成本之FemtoPBX網路架構設計

Abstract

電信營運商已經非常普遍地布建蜂巢式網路，用來提供電話語音與數據服務給行動用戶使用。但最近幾年來，由於行動電話費率的降低、新的使用者裝置及新應用服務的出現，很多的行動用戶即便在室內的環境，仍然會繼續使用行動裝置，而捨棄使用固網裝置，使得室內的行動通訊流量大增。然而，第三代或第四代的無線通訊信號從室外進入室內，會有很明顯的信號衰弱，使得室內行動無線網路的覆蓋率及容量嚴重地不足。為了傳輸室內大量的行動通訊資料，電信營運商必須提供更好的室內網路覆蓋率並提昇網路容量。可是若在建物的附近布建更多的戶外基地台將嚴重地增加行動網路基礎設施的建設成本。 Femtocell網路是在一個小區域內(如建物內部)布建涵蓋範圍小且低功率的Femto型基站，可以有效解決蜂巢式網路在室內網路覆蓋率及容量不足的問題。本論文提出一個Femto型私有交換機(FemtoPBX)的架構，在此架構下，某一分散或集中的特定區域中，所有Femto型基站的通話與資料流，都集中到Femto型私有交換機(FemtoPBX)處理。經由FemtoPBX，二個都在Femto型基站內用戶的通話，可以被轉換為成本較低的內線分機的通話，因此通話路由的成本也會明顯地降低。本論文所提Femto型私有交換機(FemtoPBX)的方法，不須要修改既有行動網路中的任何節點。本研究詳細地分析了FemtoPBX通話路由的效能，並且發展了模擬實驗來對照驗證分析模式。 在蜂巢式網路中，所有相容於標準規格的網路元件產品，都必須具有互通性。FemtoPBX在蜂巢式網路中是一個新的節點，因此FemtoPBX的相容與互通性也都必須被展現並確認。為此，本論文也設計了二個以TTCN-3框架為基礎的測試工具—ITRI-WiMAXT與NTP-SIOT，ITRI-WiMAXT是用來確認FemtoPBX在WiMAX網路中，網路層面的相容互通性，NTP-SIOT是用來確認在UMTS網路中，FemtoPBX不會影響應用服務層面的互通性。 本論文研究成果顯示，使用FemtoPBX的方法，在增加少量的正常通話連接訊號的成本下，可以有效地降低Femtocell用戶的通話建立與語音骨幹的成本。研究的成果也展示了FemtoPBX在既有蜂巢式網路的互通性，不會影響到既有的通訊應用服務。

Cellular networks have been widely deployed to provide telephone and data services for mobile users. However, mobile users have generated heavy mobile traffic indoors in recent years. To meet the transmission requirements of indoor users, cellular operators must provide better indoor coverage and network capacity. However, deploying more base stations (BSs) for indoor coverage and capacity may significantly increase the cost of the mobile network infrastructure. The femtocell concept is an effective way to improve indoor coverage and capacity for cellular networks. This approach involves deploying short-range, low-power BSs, called Femto BSs, in small areas (e.g., buildings). This dissertation proposes a Femto Private Branch Exchange (FemtoPBX) design to concentrate the Femto BS traffic in a specific area, such as a campus or an enterprise with central or distributed locations. The FemtoPBX replaces a normal cellular call between two Femto users by a low-cost extension call. This approach significantly reduces call routing costs, and does not modify existing mobile network nodes. This study analyzes the call routing performance of the FemtoPBX, and presents simulation results to test the analytical model. The FemtoPBX is a new component of modern cellular networks. Interoperability among cellular network elements is required to support all products that comply with standard specifications. As such, all of the network equipment used in a cellular network must demonstrate interoperability, including the FemtoPBX. This dissertation confirms the network level interoperability of FemtoPBX in a WiMAX network environment by designing and implementing the ITRI-WiMAXT test suite, based on the TTCN-3 framework. This study also uses the NTP-SIOT test suite to confirm the service-level interoperability of FemtoPBX in a 3GPP UMTS network environment. The results of this study indicate that the FemtoPBX approach can effectively reduce the call setup costs and voice trunk costs of Femto users with only a slight increase in normal cellular call setup costs. This study also demonstrates that the FemtoPBX is interoperable with existing cellular networks.