基於WiFi 技術之真實室內無線網狀網路Bunnet 系統實作與效能評估

Abstract

在無線網路裡，有多個通道可以使用。透過同時使用不同通道來傳輸的方式，可以增加多重傳輸數量和減少干擾影響。在多通道(Multi-channel)無線網路中，一項重要的效能議題是如何有效率地利用通道的多樣性達成同時傳輸。對於單網卡的設備而言，它只能使用單通道無線傳輸。如果同時有多台設備進行傳輸，將會導致干擾變多，使得網路系統吞吐量(throughput)下降。另一方面，在多通道無線網路的環境中，藉由使用不同通道進行傳輸，可減少干擾的影響和降低傳輸封包的碰撞機率，並且獲得較高的網路系統吞吐量。然而，大部分的無線網路設備通常都只配置單張網卡，無法利用多通道的優勢。在本論文裡，我們利用基於WiFi技術的單網卡無線網路設備(Meraki mini)來架設一個真實室內無線網狀網路(Bunnet)。我們將兩台單通道無線網路設備結合在一起，成為一個可存取多通道的無線網路節點，而該節點內的兩台網路設備使用Ethernet的方式來連結，再新增、修改Meraki內部的路由程式，來實現多通道無線網路。經由實驗結果可以看出，我們配置的無線網路節點可以利用多通道無線網路的優勢，達到更高的網路吞吐量。

IEEE 802.11 wireless network supports the utilization of multiple available channels. Using different channels simultaneously, we can increase transmission pairs and reduce interference. In multi-channel wireless networks, one essential performance problem is how to effectively exploit channel diversity to enable concurrent communications. For a single-radio device, it can only access one channel to transmit data. If there are multiple single-radio devices attempting to send at once, it will cause more collision and interference in the environment. One the other hand, in multi-channel wireless networks, using different channels to transmit data would reduce collision and interference, hence better system throughput can be produced. Most off-the-shelf wireless devices are equipped with one wireless interface card, which means that it can only access one channel at a time. In this thesis, we use single-radio wireless devices (Meraki mini) to construct an operational WiFi-based indoor wireless mesh testbed. We combine two devices into one node with multi-channel capability. The devices communicate with each other over Ethernet port. By modifying the functions of Meraki, we can use single-radio device to construct a multi-channel wireless mesh network. From the experimental results, we demonstrate that combining two devices into one node with multi-channel capability is not only feasible, but also achieves higher throughput than a typical ordinary single-channel wireless mesh network does.