臺灣博碩士論文加值系統

IEEE 802.15.4標準定義了低速率無線個人區域網路(LR-WPANs)中實體層(physical layer, PHY Layer)和媒體存取層(medium access control layer, MAC Layer)的協定。根據最新的IEEE 802.15.4標準，服務品質(quality-of-service, QoS)可以藉由保證時間槽(guaranteed time slots, GTS)的機制來達成，因為在保證時間槽之內傳輸資料不需要競爭頻寬使用權。在IEEE 802.15.4標準中，保證時間槽是由PAN coordinator使用先到先服務(first-come-first-service, FCFS)的策略來配置的，但是它缺乏了優先權的考量。在此篇論文中，我們針對保證時間槽的配置提出了一種優先權強化機制。藉由這個機制，我們可以保證擁有越高優先權的資料可以越快得到頻寬使用權來傳送即時性(Real-time)封包。從模擬的結果可以得知，我們的機制跟原來的機制比起來有較多的GTS配置數、較高的Throughput、較好的頻寬使用率以及較低的封包傳輸延遲時間。

IEEE 802.15.4 standard defines the physical (PHY) layer and medium access control (MAC) layer protocols for low-rate wireless personal area networks (LR-WPANs). In IEEE 802.15.4 LR-WPANs, quality-of-service (QoS) is supported by using the guaranteed time slots (GTS) to transmit real-time packets since a LR-WPAN device doesn’t need to contend the channel in the GTS. In the PAN coordinator, requests of GTS are allocated based on the first-come-first-service (FCFS) policy. However, with the increasing of multimedia applications, this original design has suffered from the lack of priority mechanism to support the transmission of real-time packets. In this thesis, I propose a non-preemptive priority-based polling scheme for the GTS allocation in IEEE 802.15.4 LR-WPANs. The proposed scheme can ensure that the connections which have higher priority can transmit real-time packets quicker. The simulations show that the proposed scheme can achieve more GTS allocations, higher throughput, better bandwidth utilization and lower packets access delay time.

Table of contents
摘要 I
Abstract II
誌謝 III
Table of contents IV
List of figures VI
List of tables VII
Chapter 1 Introduction 1
1.1 Motivation 1
1.2 Related Works 3
1.3 Contributions 4
1.4 Organization 4
Chapter 2 Preliminary 5
2.1 Superframe Structure 5
2.2 GTS Management 6
2.2.1 GTS Allocation 6
2.2.2 GTS Deallocation 7
2.2.3 GTS Reallocation 7
2.3 Slotted & Unslotted CSMA/CA Mechanism 8
2.3.1 Slotted CSMA/CA Mechanism 9
2.3.2 Unslotted CSMA/CA Mechanism 11
Chapter 3 Proposed Scheme 12
3.1 Call Admission Control 12
3.2 Packet Transmit-Permission Policy for Real-Time Flow 14
Chapter 4 Performance Evaluation 17
4.1 Simulation Environment 17
4.2 Simulation Results 19
Chapter 5 Conclusion 24
Appendix 25
Bibliography 26

List of figures
Fig. 1. Two types of network topology in LR-WPANs 2
Fig. 2. Superframe structure 6
Fig. 3. GTS reallocation 8
Fig. 4. Slotted CSMA/CA mechanism 10
Fig. 5. Unslotted CSMA/CA mechanism 11
Fig. 6. State transition diagram 13
Fig. 7. Proposed packet transmit-permission policy 15
Fig. 8. Executing time versus number of real-time flows 19
Fig. 9. Number of GTS allocations versus number of real-time flows 20
Fig. 10. Throughput versus number of real-time flows 21
Fig. 11. Bandwidth utilization versus number of real-time flows 22
Fig. 12. Average access delay time versus number of real-time flows 23


List of tables
Table 1. Parameters used in CSMA/CA mechanism 8
Table 2. Default attribute values used in simulations 18

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