Research And Improvement Of Routing Metric In Wireless Mesh Network

With the high-speed development of mobile internet and the rapid adoption of wireless terminals such as smart phone or tablets, Wireless Mesh Network(WMNs) as a kind of broadband wireless access networks has been paid attention by more and more people. With the characteristics of broadband, self-organizing, multi-hop, high robustness, self-healing and so on, WMNs is a key technology to solve the wireless coverage of “last mile”. As a measure standard of a link’s quality, routing metric directly affect the performance of WMNs. So the routing metric is an emphasizing research topic in WMNs.This thesis summarized the characteristics and factors that a routing metric should possess or consider. A good routing metric should possess stability, optimality, isotonicity and consider the impacts of these factors, such as path length, packet loss rate, bandwidth, load, interference, channel diversity and so on. By analyzing the Airtime Link Metric(ALM), we found that it does not consider the influence of interference and load. Aiming at the shortcomings of ALM, this thesis proposes an improved routing metric named Enhanced Airtime Link Metric(EALM). Different from the ALM, the new EALM metric also takes the impacts of interference and load into account. Since the end-to-end delay consists of not only the transmission delay but also the queuing delay in the buffer, so the EALM takes the queuing delay into account and thus indirectly considers the load. Using the total link bandwidth to calculate the transmission delay in ALM is not accurate, since the performance of the link which bandwidth is high but very busy is not better than the link which bandwidth is low but not busy. So EALM uses link’s residual bandwidth to calculate the transmission delay. EALM uses the physical interference model to calculate the Interference Degree Ratio of a node and then calculate the link’s residual bandwidth. This thesis uses NS3 to simulate the performance of EALM, hop and ALM, the results show that EALM performs better than hop and ALM in end-to-end delay, delivery ratio and throughput. After considering the interference and load, EALM can effectively avoid the path which has strongly interference and heavily load, thus enhance the performance.Research shows that, using multi-interface multi-channel can greatly improve the capacity of WMNs. So this thesis proposes a new routing metric named Weighted Cumulative EALM(WCEALM) which is suitable for multi-interface multi-channel WMNs. WCEALM consists of two part, the first term is the sum of EALM along all hops in the path and it captures how much a flow along the path utilizes the channel resource in the network, the second term is the sum of each node’s channel switching cost(CSC) along the path which is similar to the Metric of Interference and Channel-switching(MIC) and the CSC component represents intraflow interference. The MIC takes only two hop’s channel assignment into account, but the interference range is usually greater than two hop. So the estimation of intraflow interference in MIC is not accurate. WCEALM’s CSC consider the channel assignment of three consecutive links, so it can capture the intraflow interference more accurate than MIC. WCEALM is not an isotonic path weight function if used directly in the real networks, however, it has been proved that virtual network decomposition can solve the non-isotonicity problem caused by CSC. Using NS3 to simulate the performance of WCEALM and WCETT, the results show that WCEALM performs better than WCETT in end-to-end delay, delivery ratio and throughput. After considering the interference, load and introducing the CSC to estimate the intraflow interference, WCEALM can find out the path with less interference, light load, good channel diversity more accurate than WCETT.