Practical Consideration of Routing Protocols in Ad Hoc Networks

Abstract

In this dissertation, we investigate different routing approaches in an attempt to improve the network performance by considering how wireless networks operate in the realistic environment. Our work is centered around two primary focuses: In the first one, we have found that disruptive links appear quite frequently due to the presence of obstacles and node mobility. In the presence of disruptive links, we studied how geographic routing protocols, such as GPSR, should be properly adapted and proposed the Disruption Tolerant Geographical Routing protocol (DTGR). In the second half, we consider the routing problem in multi-radio multi-hop wireless mesh networks. To maximize the overall throughput of such a wireless mesh network, the interference between mesh routers need to be taken into account. We formulate the impact of the interference into a cost function and proposed the Cost Aware Route Selection scheme (CARS). In a wireless ad hoc networks where temporary link disruptions occur frequently, a node may have incorrect perception of its neighbor set. Since the neighbor set is constructed via beacon sampling, beacon collisions may result in the removal of a node from the neighbor set even though the node is still within the transmission range. Such a behavior can adversely affect the performance of position based routing algorithms as it may lead to inefficient routing or packet dropping. To address this, we propose a scheme that allows each node to associate each of its neighbor with a reachability value that is a measure of the stability of the link. We then apply our scheme to Greedy Perimeter Stateless Routing (GPSR) and design two new routing algorithms, namely Disruption Tolerant Geographic Routing-Simple Forwarding (DTGR-SF) and Disruption Tolerant Geographic Routing-Waiting before Forwarding (DTGR-WF), in which nodes utilize reachability values to make appropriate forwarding decisions. We compare the performances of DTGR-SF and DTGR-WF with that of GPSR in various simulation settings. Our simulation results show that our proposed algorithms perform better in settings where link disruptions are present. In networks with few occurrences of disruptions, our schemes achieve the same high performance as that of GPSR. Many applications of wireless mesh networks, such as WLAN, video conference, and VoIP, demand more bandwidth and the support of more active users. By installing multiple radio interfaces at each mesh router, a wireless mesh network is able to better utilize the available wireless spectrum for such applications. However, the presence of multiple radio also complicates the selection of route in wireless mesh networks. To address this issue, we first use a cost function to capture the degree of interference for a given route quantitatively. We then propose a novel metric that measures the bandwidth and cost ratio of each route. Based on this metric, a Cost-Aware Route Selection (CARS) scheme is proposed to improve the overall throughput of a mesh network. The simulation results confirm that our scheme is able to better utilize the limited wireless resource and improves the overall network throughput by more than 95% with different types of traffic and communication patterns when it is compared against the past route selection schemes.