在無線網路中針對優先權傳送之排程技術研究

Abstract

在越來越競爭的電信市場上，電信業者如何能同時滿足用戶服務的滿意度和保持各項業務的盈收是相形重要。論文中針對幾種不同無線網路型態(如GPRS, 3G , HSDPA)的用戶在使用無線資源時，除考量傳送或接收封包優先權排程方式之外，另針對吃到飽( flat-rate)用戶，考量其對行動業者的最有效率優先權排程機制，做了廣泛且深入之研究。 首先在GSM 行動網路中，我們研究和比較3種不同排程方式，如何在用戶傳送上傳(uplink)封包時，控制和調整用戶的上傳封包的傳送優先權，透過建立數學分析模式和幾種不同分析參數，比較何種優先權考量可滿足用戶服務滿意度。研究發現利用上鏈路狀態旗標(USF)配置的排程方式可以讓有較高優先權封包(如VoIP)，其傳輸延遲可以比較少。 接著，在UMTS 行動網路中，我們研究和比較4種不同排程方式，如何在用戶啟動上傳連線(uplink connection transmission)時，控制調整用戶的上傳連線的傳送優先權，透過建立數學分析模式、幾種不同分析參數和考量吃到飽用戶所提出的代價函數(cost function)，來比較何種優先權考量可同時滿足用戶服務滿意度和保持電信業者盈收。研究發現單憑降低用戶的上傳連線速度，並不會讓整體用戶的上傳連線傳送效能最高和讓電信業者擁有最大盈收，若利用等待隊列(waiting queue)和強制取代(preemption)的排程方式，可以同時兼顧用戶服務滿意度和讓電信業者擁有最大盈收。 最後，在HSDPA 行動網路中，我們研究和比較4種不同排程方式，如何在用戶傳送下傳(downlink)封包時，控制調整用戶的下傳封包的傳送優先權，透過建立數學分析模式、幾種不同分析參數和考量吃到飽用戶所提出的代價函數(cost function)，比較何種優先權考量可同時滿足用戶服務滿意度和保持電信業者盈收。研究發現若利用等待隊列(waiting queue)和固定強制取代(preemption)的排程方式，並不會讓整體用戶的下傳封包傳送效能最高和讓電信業者擁有最大盈收，若考量加入動態丟棄計時器(Drop Timer)和動態防護通道(Guard Slot)的排程方式，來動態調整用戶下傳封包的傳送優先權，可以同時兼顧用戶服務滿意度和讓電信業者擁有最大盈收。 在無線網路發展趨勢上，電信業者必須持續不斷的研究如何能同時滿足用戶服務的滿意度和保持各項業務的盈收。本篇論文研究的結果可被當成繼續研究在無線網路中如何考量優先權排程方式的基礎。

In today’s highly competitive telecommunications environment, the emphasis has shifted to delivering innovative services to satisfy increasingly sophisticated customers’ need and to improve the revenues of wireless operators. This dissertation has studied different scheduling mechanisms for priority transmission in public land mobile networks (PLMNs). We considered not only the priority in packet transmission/reception using various scheduling techniques, but also the most efficient mechanisms for serving both normal and flat-rate customers. First, we study and compare three different scheduling mechanisms in the GSM network. As the General Packet Radio Service (GPRS) network begins to provide such as "push-to-talk" (PTT) service, delay-sensitive packets should be given higher priority in transmission. In this paper, we study two channel allocation schemes that implement priority queues for priority packets in the GPRS network: Bitmap Channel Allocation (BCA) and Uplink State Flag Channel Allocation (USFCA). Our study shows that the transmission delay of priority packets in the GPRS network can be better guaranteed using USFCA. Second, we study and compare four different scheduling mechanisms in the UMTS network. To attract more users to mobile packet services, the Universal Mobile Telecommunication System (UMTS) operators have been prompting flat-rate packet services. Since usage does not incur cost, flat-rate users tend to stay on line longer and occupy most of the radio channel resources. We consider a UMTS network serving two types of user connections: Normal User Connections (NUCs) and Flat-Rate User Connections (FRUCs). Our goal is to maximize the revenue of the operator by giving a priority to NUCs over FRUCs without discontenting the flat-rate users, in order not to lose the flat-rate users to other operators. Uplink FRUCs may be asked to sub-rate or suspend transmission when the radio network is fully utilized. Four combinations of scheduling techniques including queueing, guard channels, preemption and rate-adaptation, have been studied, and analytic models using Markov processes were used to evaluate their performances. We proposed a cost function representing the revenue loss due to both blocked NUCs and lost flat-rate users. The system parameters used in our analysis are based on realistic operation data. Our analytic results indicate that the revenue loss can be minimized by using waiting queues and preemption. Rate-adaptation is ineffective in minimizing the revenue loss because sub-rated connections are less efficient in using radio spectrum. Guard channels for NUCs are unnecessary when waiting queue or preemption is used. Our study may be valuable for UMTS operators in serving flat-rate users. Third, we study and compare four different scheduling mechanisms in the HSDPA network. We consider a HSDPA network serving two types of user packets: charged packets (CPs) and flat-rate packets (FRPs). Since CPs are charged by usage, they are given a higher priority to receive downlink packets for revenue consideration. However, this priority preference may lead to poor quality of service for flat rate users. In particular, FRPs may experience longer transmission latency and higher dropped probability. We should consider the balance between serving the FRPs and CPs. Analytic models using Markov process were used to study their performance. Our study shows that DDT-PQ and DGS-PQ methods are more effective to transmit the downlink CPs especially when the downlink FRP traffic is high. Therefore, they are better in guaranteeing the system throughput for CPs, and thus the operator revenue can be better protected. In the development trend of wireless network, wireless operators need to keep studying how to satisfy the QoS requirements of the customers and have the best revenues at the same time. The research results presented in this dissertation can be viewed as a useful foundation for further study in the scheduling mechanisms for priority transmission in the wireless network.