IEEE 802.11 기반 멀티 채널 멀티 레이트 무선 메쉬 네트워크에서의 레이트 분할을 위한 채널 할당 프로토콜

Abstract

Wireless Mesh Networks (WMNs) have received an increasing interest to offer broadband Internet accesses. For WMNs, various wireless technologies can be used such as IEEE 802.11, IEEE 802.15, IEEE 802.16, and so on. However, the most popular technology is IEEE 802.11. The off-the-shelf IEEE 802.11 PHY and MAC specifications support both multi-channel and multi-rate capabilities. One of challenging issues in WMNs is designing an efficient channel assignment protocol that exploits both available channels and data rates. In IEEE 802.11 multi-rate wireless networks, a wireless link can use one of data rates defined in IEEE 802.11 standard. As a result, high-rate links and low-rate links may operate on the common wireless channel. In such a case, high-rate links heavily suffer from performance degradation due to the presence of low-rate links. This problem is known as rate anomaly (or performance anomaly). To mitigate this problem, various protocols have been suggested in IEEE 802.11 single-channel networks. Specifically, these protocols require modifications to the commodity IEEE 802.11 devices. To mitigate rate anomaly without 802.11 modifications in multi-channel networks, several channel assignment protocols have been proposed by assuming multi-channel single-hop wireless networks. For multi-channel multi-hop wireless networks, only a few channel assignment protocols have been suggested. In this thesis, we propose two multi-channel protocols to alleviate the rate anomaly problem in IEEE 802.11 multi-channel multi-rate WMNs. First, we propose a cooperative channel assignment (CoCA) protocol. CoCA exploits the estimated delivery time (EDT) metric and an efficient balancing algorithm. Using the EDT metric, CoCA performs channel assignments to form multi-channel multi-hop paths (MMPs) so that it separates high-rate links from low-rate links over different channels and increases the channel diversity. In addition, CoCA utilizes the balancing algorithm to consider the rate anomaly problem and throughput fairness during channel assignments. Second, we propose a distributed family-based channel assignment (FCA) protocol. We identify the rate anomaly problem in multi-hop multi-rate networks, and introduce an extension of conflict graph, rate conflict graph (RCG), to model this problem. Based on the family architecture, FCA improves channel diversity, node connectivity, and capacity of WMNs by using a channel assignment and routing metric, heuristic algorithms, and RCG. We evaluate the performance of CoCA and FCA through extensive ns-2 simulation and experiments on our real test-bed. The evaluation results show that CoCA and FCA outperform existing channel assignment protocols designed for WMNs.