Performance evaluation of channel assignment and congestion control techniques in multi channel wireless mesh network

Abstract

A Wireless Mesh Network (WMN) consists of numerous fixed access routers which are linked to one another to connect the mobile nodes similar to conventional Wireless Local Area Networks (WLAN). These access routers are capable of communicating with one another through multiple hops. Some of them are connected to the Internet through wired links to act as internet gateways for the network. Channel assignment is the main problem in WMNs while handling multiple radios and channels. In a WMN, the backbone network capacity decreases owing to interference of the wireless communication. Hence appropriate channel assignment becomes critical in multi-channel multi-radio WMNs. In order to maximize the performance gain, joint implementation of routing and channel assignment are very important. To solve the issues of channel assignment and gateway selection, this thesis presents a dynamic channel allocation and gateway selection algorithm for multi-channel hybrid WMNs. In this algorithm, the dynamic gateway selection method is extended by incorporating channel quality and switching cost along with queue length. A combined cost metric, comprising queue length, Channel Switching Cost (CSC) and Expected Transmission Time (ETT) of the source node for each gateway is determined. The gateway with least rate metric is chosen by the base nodule. Then a temporal channel assignment scheme is used for assigning the channels to the selected gateway. Load balancing becomes important as the traffic volume is expected to be very high in a WMN. Congestion affects network performance metrics such as throughput and delay. Some gateways are affected by congestion problems, whereas others are severely underutilized. This thesis presents congestion aware gateway load balancing technique for multi-channel WMNs to handle these problems. In this technique, when a mesh client wants to transmit a data to its gateway node, it chooses the track with least load centered on the Interface Queue Length (IQL). If blockage is identified at any transitional nodule, then the router detects the congestion on the basis of the Exponentially Weighted Moving Average (EWMA) of the queue size. newline