結合跨層設計之頻道分配演算法

Cross Layer Design of Multicasting and Channel Allocation for MCMR WMNs

無線網狀網路（Wireless Mesh Networks, WMNs）是近年來新發展出的無線網路架構，WMNs具有與傳統有線網路截然不同的特性，其中包含隨時可能改變的網路型態、沒有方向或範圍限制的移動、涵蓋範圍極大等等。設想在一個都市區內，許多人想要收看相同的即時視訊，若用單一傳播（Unicast）的方式，則會浪費很多頻寬，最好的做法是在WMN上利用群體廣播（Multicast）的方式，提供即時視訊的服務給大量的使用者。在頻道數目有限的情況下，有些路由路徑無法分配無干擾頻道，導致此路徑底下的用戶無法收到影音串流，因此，頻道分配成為在WMNs上建立群播樹最重要的問題之一。本論文提出一個結合跨層設計之調整式頻道分配演算法，目標是最大化成功接受影音串流的用戶數目且能穩定傳輸串流，本演算法同時進行建立群播路由和頻道分配，加上可調整頻道的程序，使得整體效能能夠更進一步的提升。本論文的最後利用完整且嚴謹的實驗和之前的演算法進行比較，並使用模擬軟體Qualnet模擬和評估此演算法。

Wireless Mesh Networks (WMNs) are a new broadband Internet access technology with characteristics different from the traditional wired networks, including self-organization、self-management、self-healing and wide coverage. In this paper, we consider a video/audio delivering system deployed on the multi-channel multi-radio (MCMR) wireless mesh networks, where a number of mesh clients serviced by different mesh routers may subscribe the same video/audio program supplied by a multimedia server installed on the gateway node. For this scenario, multicast would be a better mechanism than unicast to deliver video streams to clients in real time, since only one copy of packets is required to send in multicast protocols. However, with the limited number of channels, some links in the multicast tree may not be allocated with interference-free channels. As a result, some client in the multicast tree may not receive video streams. Therefore, channel allocation has become one of the key problems for constructing multicast tree in WMNs.In this paper, we propose an algorithm to construct an interference-free multicast tree for WMNs. Our goal is to provide high quality video streams and maximize the number of clients who can successfully receive streams they subscribed. Based on cross-layer design paradigm and considers network routing and channel allocation at the same time during the formation of trees. Also, a channel adjusting procedure is provided to improve the quality of the resulting tree. Finally, several sets of experiments are given to evaluate the performances of our algorithm.