A Routing Approach for Multi-channel Wireless Ad-Hoc Network with Single Transceiver

無線區域網路允許行動使用者在不依賴事先建構的通訊架構下交互連結，但是當網路中的行動使用者增加時，整體系統的效能將受限制，其影響因素之一為行動網路中的使用者皆共用相同的頻道，若數個無線節點在彼此干擾範圍之內，它們必需要依據 IEEE 802.11 所定義之DCF協定來互相競爭媒介的使用權，如此將會降低網路的存取能力。 然而，IEEE的標準中允許無線裝置在實體層使用多個通訊頻道，可是在上層的網路通訊協定卻只被設計與使用於單一頻道的環境下。除此之外，在多頻道環境會衍生出多頻道隱藏點問題，基於此問題，單一頻道協定並不適合用於多頻道無線環境，而且單一頻道協定也無法利用多頻道的好處，例如使用多頻道通訊可在特定區域內平行進行而彼此不會相互干擾。 在本論文當中，我們研究一套應用於多頻道無線區域網路之路由方法，我們的協定只要求每個無線節點裝備單一具有切換頻道能力之收發器，不需要額外的硬體或是修改到MAC協定的部份。最後，我們亦會利用模擬來評估我們協定的效能，由模擬結果指出在多頻道無線網路中，使用我們的多頻道路由協定可以有效的提升系統效能。除此之外，我們亦會於此論文當中探討相關於多頻道網路協定之設計考量、影響因素、和其它相關的研究議題。Wireless ad-hoc networks allow mobile users or devices to seamlessly interwork in areas without any pre-existing communication infrastructure. However, the networks may suffer from rapid performance degradation as the number of users increases. One reason for the performance degradation is the fact that all nodes in the network share the common channel. If one node is within the interference range of others, it must to content the channel according to IEEE 802.11 DCF protocol, and this degrades the network performance. Hence, The IEEE standard allows the use of multiple channels available at the physical layer, but the upper layer protocol is only designed for single-channel environment. The single-channel protocol is not suitable in multi-channel environment due to the multi-channel hidden terminal problem. Furthermore, it also cannot take advantage of the benefit of multi-channel environment, e.g. multi-channel communication can simultaneously take place in the same region without interfering each other. In this thesis, we study a routing protocol for wireless ad hoc networks that utilizes multiple channels dynamically to improve performance. Our protocol only requires a single transceiver with functionality of dynamically switching per host without using any additional hardware or modifying the MAC protocol. We also evaluate the performance of our protocol by simulations. The results show that our proposed protocol can significantly improve the performance in multi-channel environments. In addition, we also discuss the considerations, impact factors, and other research issues for designing multi-channel protocols.Abstract X Chapter 1 Introduction 1 1.1 Current Wireless Networking 2 1.2 Motivation and Objective 3 1.3 Organization 4 Chapter 2 Background and Related Works 5 2.1 Background 5 2.1.1 Wireless LANs Infrastructure 5 2.1.2 Multi-channel Ad-hoc Networks 7 2.1.3 Review of Ad-hoc On-Demand Vector Routing 8 2.2 Related Works 11 2.2.1 Multiple-channel Researches 11 2.2.2 Multi-radio Researches 15 2.2.3 Summary 23 Chapter 3 Multi-channel Routing Protocol 25 3.1 Multiple-Channel Protocol Design Issues 25 3.1.1 Channel Assignment 26 3.1.2 Path and Channel Diversity 31 3.2 Integrate Multi-channel Design Issues to Routing Protocol 33 3.2.1 Define Node States 33 3.2.2 Route Discovery 35 3.2.3 Channel Assignment and Path Select Mechanism 38 3.2.4 Packet Forwarding and Channel Switching 43 3.2.5 Force Mechanism 44 3.2.6 An Example for Multi-channel Routing Protocol 45 Chapter 4 Implementation and Discussion 47 4.1 System Assumptions 47 4.2 Simulation Tool 48 4.2.1 Mobile Networking 49 4.2.2 Multi-channel Support 51 4.3 Simulation of Multi-channel Routing Protocol 53 4.3.1 Simulation Environment and Network Configuration 53 4.3.2 Measurement of the Simulation 54 4.3.3 Simulation Result and Analysis 55 4.4 Other Discussions 62 Chapter 5 Conclusion 65 References 66 Appendix: Abbreviations 7