無線網路之封包排程與資源保留支援方案

Abstract

下一代行動通訊(Next Generation Mobile Communications)即將帶給人類新一波生活型態上的革命，工作時間和休閒時間的分野將會變得越來越模糊，因為新的行動通訊系統能夠提供行動使用者隨時隨地連上網際網路(Internet)，如網頁瀏覽、存取電子郵件、資訊檢索和召開視訊會議…等應用。在新的行動通訊系統之中，第二•五代的通用封包無線電服務(General Packet Radio Service, GPRS)和第三代的全球行動通訊系統(Universal Mobile Telecommunications System, UMTS)是兩種最被廣泛接受的行動通訊系統。GPRS旨在提供細胞通訊網路中的封包交換(packet switched)資料服務。UMTS的目標是進一步地支援多媒體的傳輸服務，因為多媒體的傳輸服務極可能成為下一代資料服務中的一項最重要的服務。為了滿足多媒體資料傳輸時的即時和變動位元速率(Variable Bit Rate, VBR)的要求，下一代行動通訊系統需要利用適當的服務品質(Quality of Service, QoS)支援方案，以便針對VBR連線執行流量排程和頻寬保留的工作。此外，因為要有效提昇頻寬的使用效率，這些服務品質支援方案必需執行多條VBR連線之間的頻寬分享。 在本論文中，我們為了VBR連線從發送端到接收端中不同網路的不同傳輸特性，提出三個服務品質支援方案，去達成VBR連線的端點到端點(End-to-End)服務品質控制的目標。這些服務品質支援方案包括兩個分別在GPRS和UMTS無線電存取網路中的無線電頻道排程方案，和改良下一代行動通訊之核心網路效率及加強QoS支援的標籤交換(label-switch)架構。我們所提出的的服務品質支援方案，能夠和目前在有線Internet網路中已被提出的服務品質支援方案一起運作，沿著一條傳送路徑跨越有線和無線網路的VBR連線，提供端點到端點的服務品質控制。 針對GPRS無線電存取網路而言，我們提出一個資料流排程架構，此排程架構能夠根據VBR連線的服務品質規格和頻道的干擾狀況，動態地分配無線電頻道的個數。其基本想法是去維持比較多的頻寬給那些位於低干擾區域的VBR連線，所以我們能夠在滿足VBR連線之服務品質的前提下，更有效地使用寶貴的無線電資源。另一方面，針對UMTS無線電存取網路，我們提出一個具服務品質察覺及依據信號強度分類之封包排程(power-strength classified packet scheduling, PCPS)方案，它能夠在VBR連線建立之時，先將其信號強度劃分成若干等級並決定每一個等級的核定服務速率。當VBR連線傳輸之時，PCPS方案能夠於維持所有連線錯誤率要求的前題之下，根據目前連線的信號強度等級，動態地調整每一條連線的下傳鏈結傳輸速率。藉由此類信號強度分類的排程，PCPS方案能夠降低平均的封包延遲和提昇UMTS無線電存取網路的頻寬使用效率。 此外，我們也利用多協定標籤交換(Multi-Protocol Label Switch, MPLS)的概念，將MPLS植入下一代行動通訊系統核心網路的協定堆疊中。藉由所植入的MPLS其標籤交換的路由能力，能夠加速封包的路由，並且消除IP-in-IP隧道傳送的需要，也因此降低核心網路的傳輸延遲和提昇頻寬的使用效率。除此之外，我們利用所植入的MPLS進一步地增強核心網路，使其能夠支援服務品質保證的封包傳遞和平滑換手(Smooth handoff)於VBR連線。 我們已經實施效能評估於本論文中所提出的每一個服務品質支援方案。效能評估的結果證實所提出的方案真正都能夠保證每一位行動使用者的服務品質要求，例如，保證最大封包傳輸延遲、封包丟失率、連線中斷率等，並且能增進系統的性能，例如，允許較多的連線數和提昇頻寬的使用效率。

Next Generation Mobile Communication systems will bring a new wave of revolution to people’s lifestyle. Office hours and leisure time are becoming indistinguishable because new mobile communication systems enable users to access Internet at anytime and in any place for various applications, such as Web browsing, electronic mailing, information retrieval, video conferencing, and etc. Among of the new mobile communication systems, the 2.5 generation (2.5G) General Packet Radio Service (GPRS) and the third generation (3G) Universal Mobile Communication System (UMTS) are two of the most widely acceptable mobile packet data communication systems. GPRS aims to provide packet switched data services over cellular communication networks. UMTS takes a step further and aims to support multimedia transmission services because multimedia transmission services are likely to be one of the most important services in the coming future. In order to fulfill the real-time and variable bit rate (VBR) requirement of multimedia data transmission, next generation mobile communication systems need to employ appropriate Quality of Service (QoS) supporting schemes that can perform traffic scheduling and bandwidth reservation for VBR connections. Besides, these QoS supporting scheme need to perform bandwidth sharing among VBR connections in order to optimize the bandwidth utilization. In this thesis, we propose three QoS supporting schemes to accomplish the end-to-end QoS control along the path from the sender to the receiver of a VBR connection. These QoS supporting schemes include two radio-channel scheduling schemes tailored for the radio access networks (RANs), one for GPRS and the other for UMTS, and a label-switching architecture devised to improve performance and enhance QoS supports of the core networks for the next generation mobile communication systems. The QoS supporting schemes we proposed for radio access and core networks can work together with those QoS schemes proposed for wired Internet to provide an end-to-end QoS control along the path of a VBR connection across wireless and wired networks. For the GPRS radio access networks, we present a traffic-scheduling framework that can dynamically allocate radio resource to a VBR connection based on the interference levels of the radio links and the quality of service (QoS) specification of the connection. The underlying idea of the GPRS radio channel scheduling is to reserve more bandwidth to the VBR connections that are within a low interference region so that we could use the precious radio resource more effectively under the QoS constraints of the VBR connections. As for the UMTS radio access networks, we propose a QoS-aware power-strength classified packet scheduling (PCPS) scheme that can classify the transmission power-strength of a VBR connection into several classes and determine the admitted service rate of each class at connection setup time. During the connection transmission time, PCPS scheme can dynamically adjust the downlink service rate of each connection in accordance with its admitted service rate associated with its transmission power-strength class (PS-class), while retaining the Frame Error Rate (FER) requirements of all connections. With this power-strength classified scheduling, PCPS scheme can decrease the average packet delay and increase the bandwidth utilization of UMTS radio access networks. In addition, we also adopt the concept of Multi-Protocol Label Switching (MPLS) and embed MPLS into the protocol stack of the core network for the next generation communication systems. The label switched routing capability in the embedded MPLS can expedite packet routing and eliminate the needs of IP-in-IP tunneling, and thus decrease the transmission delay and increase the bandwidth efficiency of the core network. Moreover, with the embedded MPLS, we can further enhance the core network to support QoS guaranteed packet delivery and smooth handoff for VBR connections. We have conducted performance evaluation on each QoS supporting scheme proposed in this thesis. Performance results show that our schemes can indeed guarantee the QoS requirements, such as maximum packet transmission delay, packet dropping ratio and connection blocking ratio, for mobile subscribers, and furthermore can also increase the system performance, such as number of admitted connections and utilization of bandwidth.