IEEE 802.11 無線網狀網路下單一天線多頻道管理之協定設計

Abstract

無線網狀網路是下一代無線通訊中蓬勃發展的技術之一。在展現更大範圍的網路覆蓋率的同時，無線網狀網路也必須面對多重跳躍網路所需要面對的延伸問題 (像是吞吐量、延遲跟封包傳輸率等)。對於這一些問題來說，使用多頻道是一個有效率的解決方法。在本篇論文中，我們提出了一個在單一天線多頻道的無線網狀網路環境下的頻道管理協定。在這個環境下，有兩個主要的問題:頻道配置跟頻道切換排程。目前我們常可以看到的解法都是讓利用變化每個節點的行為來試圖解決這兩個問題，但是，我們的觀察發現在上述網路環境下，有很多的節點其實是不需要考量頻道排程切換的問題。事實上，在有許多節點不做頻道切換的網路環境下，我們還是可以同時保有多頻道協定所帶來的好處 (頻道空間再使用) ，在本篇論文中，我們將網狀網路上的節點分成兩個集合，在第一個集合上的節點都只需要待在某一個固定的頻道上進行封包的傳輸，而第二個集合上的節點會在頻道之間做切換。經由這樣的設計，我們可以降低頻道切換的負擔 (如切換延遲跟同步飄移等) ，除了經由模擬來驗證這多頻道管理協定的效能，我們還將我們的協定實做在真實的無線網狀網路平台上 (RTL8186)。

Wireless mesh networks (WMNs) have emerged as a key technology for next-generation broadband wireless access. While benefiting from larger coverage, WMNs also suffer from some scalability problems in terms of throughput, delay, and packet delivery ratio faced by all multi-hop wireless networks. Using multiple channels is a cost-effective solution to these problems. In this paper, we propose a channel management protocol for multi-channel, single-radio 802.11-based wireless mesh networks. In such an environment, two issues should be addressed: channel assignment and channel switch scheduling. Therefore, most existing multi-channel solutions involve a channel assignment scheme and a scheduling scheme to determine nodes' behaviors at different times. However, we observe that channel switching of some mesh points may not be necessary under this environment. In fact, event without channel switching, the benefit of using multiple channels (spatial reuse) can still be achieved. In this work, mesh points are divided into two sets. Those in the first set will be assigned channels and stay in the same channels to transmit/receive packets. On the other hand, those in the second set will switch to proper channels dynamically. With this design, a lot of channel switching overheads (switching delay, synchronization drift, etc.) can be mitigated. Extensive simulations are conducted to verify the efficiency of the proposed protocol. We also implemented our proposed protocol on the RTL8186 platform.