Movement Speed Based Inter-Probe Times for Neighbour Discovery in Mobile Ad-hoc Networks Matthew Orlinski and Nick Filer School of Computer Science, University of Manchester, Manchester, M13 9PL, UK. {orlinskm,nick}@cs.manchester.ac.uk Abstract. It is widely known that topology, wireless range, and the movement patterns of devices often impose severe limitations on the ability of devices to communicate in Mobile Wireless Ad-hoc Networks (MANETs). However, there has been less research into the effect of de- vices’ movement speeds on network connectivity. In this paper we will look at two commonly used MANET movement patterns, Working Day Movement (WDM) and Random Walk Movement (RWM). This report will demonstrate using both of these movement patterns, that the time between neighbour discovery scans called the inter-probe time, can have a drastic effect on network connectivity. We will suggest a mechanism to choose inter-probe times based on the movement speeds of devices which can efficiently detect more than 99% of encounters between mobile de- vices carried by pedestrians. We will then propose a dynamic approach (PISTONS) which allows devices to alter inter-probe times based on context whilst preserving much of the network connectivity. Key words: mobile ad-hoc networks, pocket switched networks, neigh- bour discovery, inter-probe times 1 Introduction Network topology, wireless range and the movement of devices often impose severe limitations on the ability of devices to communicate in Mobile Wire- less Ad-hoc Networks (MANETs). In two specific types of MANETs, Pocket Switched Networks (PSNs), and Vehicular ad-hoc networks (VANETs), data is often exchanged in a “store-wait-forward” [1, 2] model which is constrained by the movement speed of devices [3]. Slower movement can mean longer inter- contact times, and messages are stored for longer periods. Movement speed can also impact device discoverability. When one electronic device searches for another it can either do this continuously, consuming valuable power and channel capacity [2, 4, 5], or it can probe periodically using inquiry intervals as shown in Fig. 1. During an inquiry interval, Neighbour Discovery Requests (NDREQs) [6] are broadcast, listened for and replied to resulting in encounters between devices and perhaps data connections forming between de- vices a short time after they come into range of one another.