PROGRAMA DE MAESTRÍA Y DOCTORADO EN INGENIERÍA

A Study on the Impact of Node Mobility on the Duration and Maximum Length of Multi-Hop Routes in Wireless Networks Michael Pascoe Chalke A mobile ad-hoc network (MANET) is a collection of mobile nodes forming a temporary network by means of wireless interfaces and without use of any existing network infrastructure or centralized administration. Due to the limited transmission range of wireless radio transceivers, there may be a need for one or multiple nodes (intermediate nodes) working as relays to establish a communication path between source-destination pairs in a mobile ad-hoc network. This thesis presents a model that estimates the time duration of routes formed by several intermediate nodes in mobile ad-hoc networks. First, a 3-node route is analyzed, where only the intermediate node is in movement while source and destination nodes remain static. From this case, it is shown how route duration is affected by the initial position of the intermediate node and the size of the overlapping region where it is located. The overlapping region associated to an intermediate node is formed by the intersection of the coverage zones between their adjacent route neighbors. A second case is also considered where all nodes of the 3-node routes are mobile. Based on extensive analysis of these routes, the PDF of route duration is determined under two different mobility models. This PDF can be determined by either analytical or statistical methods. Finally, this thesis shows that the time duration of a route formed by N intermediate nodes can be accurately computed by considering the minimum route duration of a set of N routes of 3 nodes each. Simulation work was conducted using the NS-2 network simulator to verify the accuracy of the proposed model and to compare it with other proposals found in the literature. Simulation results show that the model is in better agreement as compared with other models. Results from this work can be used to compute overhead signaling during route-maintenance of unicast and multicast routing protocols for mobile ad-hoc networks. This thesis also sets forth a model to compute an upper bound on route length in mobile ad-hoc networks. In MANETs, routes are usually found by means of discovery packets that are injected to the network by sender nodes. At the time of reaching an intended destination, the route followed by a discovery packet is used to send a reply packet back to the sender. Upon reception of the reply message, data transfer from sender to destination can initiate. Node mobility, however, negatively affects route duration time since position changes may lead to disruptions in connectivity. Furthermore, the whole route discovery process collapses when, due to position changes, the route followed by a discovery packet (or a reply packet) may not be valid at any time, while one of these packets is travelling across the route. This thesis examines the conditions leading to this effect and shows that they impose a practical limit on route length. This thesis also introduces a delay model for multi-hop routes which is extended from an access delay model for single-hop WLAN networks found in the literature. Another route duration model that considers forwarding delays involved during the route discovery phase is also derived in this thesis. By combining both models, a closed-form expression to compute maximum route length in MANETs is obtained. This model is validated by simulations with different network settings. From this model, it is found that the node transmission range, node mobility and forwarding delays actually define the maximum feasible number of hops in a route. To the best of the author's knowledge, this is a fundamental scaling problem of mobile ad-hoc networks that has not been analyzed before from a mobility-delay perspective.