MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Random Walkway Point (RWP) <s> An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any established infrastructure or centralized administration. In such an environment, it may be necessary for one mobile host to enlist the aid of other hosts in forwarding a packet to its destination, due to the limited range of each mobile host’s wireless transmissions. This paper presents a protocol for routing in ad hoc networks that uses dynamic source routing. The protocol adapts quickly to routing changes when host movement is frequent, yet requires little or no overhead during periods in which hosts move less frequently. Based on results from a packet-level simulation of mobile hosts operating in an ad hoc network, the protocol performs well over a variety of environmental conditions such as host density and movement rates. For all but the highest rates of host movement simulated, the overhead of the protocol is quite low, falling to just 1% of total data packets transmitted for moderate movement rates in a network of 24 mobile hosts. In all cases, the difference in length between the routes used and the optimal route lengths is negligible, and in most cases, route lengths are on average within a factor of 1.01 of optimal. <s> BIB001 </s> MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Random Walkway Point (RWP) <s> The movement pattern of mobile users plays an important role in performance analysis of wireless computer and communication networks. In this paper, we first give an overview and classification of mobility models used for simulation-based studies. Then, we present an enhanced random mobility model, which makes the movement trace of mobile stations more realistic than common approaches for random mobility. Our movement concept is based on random processes for speed and direction control in which the new values are correlated to previous ones. Upon a speed change event, a new target speed is chosen, and an acceleration is set to achieve this target speed. The principles for direction changes are similar. Finally, we discuss strategies for the stations' border behavior (i.e., what happens when nodes move out of the simulation area) and show the effects of certain border behaviors and mobility models on the spatial user distribution. <s> BIB002 </s> MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Random Walkway Point (RWP) <s> The field of delay tolerant networking is rich with protocols that exploit node mobility to overcome unpredictable or otherwise bad connectivity. The performance of many of these protocols is highly sensitive to the underlying mobility model which determines the nodes' movements, and the characteristics of these mobility models are not often studied or compared. With few exceptions, authors test their ideas using mobility models implemented on simulators written for the specific purpose of testing their protocols. We argue that it is better to unify these simulations to one highly capable simulator. We develop a suite of mobility models in OMNeT++ that specifically target delay tolerant networks. We also present a series of metrics that can be used to reason about mobility models independent of which communication protocols and data traffic patterns are in use. These metrics can be used to compare existing mobility models with future ones and also to provide insight into which characteristics of the mobility models affect which aspects of protocol performance. We implement a tool that derives these metrics from OMNeT++ simulations and implement several popular delay tolerant mobility models. Finally, we present the results of our analysis. <s> BIB003 </s> MOBILITY MODELS FOR DELAY TOLERANT NETWORK : A SURVEY <s> Random Walkway Point (RWP) <s> Mobile Delay Tolerant Networks (MDTNs) are wireless mobile networks in which a complete routing path between two nodes that wish to communicate cannot be guaranteed. A number of networking scenarios have been categorized as MDTNs, such as vehicular ad hoc networks, pocket switched networks, etc. The network asynchrony, coupled with the limited resources of mobile devices make message dissemination (also called routing) one of the fundamental challenges in MDTNs. In the literature, a large body of work has been done to deal with routing in MDTNs. However, most of the existing routing protocols are based on at least one of the following three assumptions: (1) all messages can be routed by relying on a single mobility property; (2) all messages can be routed using a single message allocation strategy; (3) users are willing to disclose their mobility information and relationships to others in order to improve the quality of the routing. We argue that the above three assumptions are not realistic because: (1) users can exhibit various social behaviors and consequently various mobility properties (e.g., they can have regular movements during week-days and exhibit non-predictable movements during week-ends); (2) some messages might need more or less copies to be delivered according to the localization of the source and the destination and to the urgency of the message; and (3) users mobility data can disclose sensitive information about the users. In this thesis, we relieve MDTN routing from the above three restrictive assumptions. Firstly, we propose an adaptive routing protocol for mobile delay tolerant networks. The proposed protocol can dynamically learn the social properties of nodes based on their mobility patterns, and exploit the most appropriate routing strategy each time an intermediate node is encountered. Simulations performed on real mobility traces show that our protocol achieves a better delivery ratio than existing state-of-the-art routing protocols that rely on a single mobility property. Secondly, we present a delay and cost balancing protocol for efficient routing in mobile delay tolerant networks. The presented protocol reasons on the remaining time-to-live of a message to dynamically allocate the minimum number of copies that are necessary to achieve a given delivery probability. Evaluation results show that the protocol can achieve a good balance between message delivery delay and delivery cost, compared with most of the existing routing protocols in the literature. Lastly, we propose an efficient privacy preserving prediction-based routing protocol for mobile delay tolerant networks. This protocol preserves the mobility patterns of a node from being disclosed by exploiting the mobility pattern of communities that node belongs to. Evaluation results demonstrate that this protocol can obtain comparable routing performance to prediction-based protocols while preserving the mobility pattern of nodes. <s> BIB004
Another basic and simplest model that is frequently used in simulation is the Random Walkway Point (RWP). RWP includes a random pause time after finishing each movement segments in the random walk. In RWP, mobility model direction angles, speeds and pause times are sampled from a uniform distribution. In simulation, random coordinates over simulation area are assigned to the nodes. Nodes move directly to the specified destination at constant speed, stay there few moments, and then acquire a new, random, destination. This continues throughout the simulation and nodes run along these zig-zag paths based on RWP model. This model is mathematically analysable and easy to implement. Thus, the researchers can easily test their own algorithms using it. This creates simple, but quite artificial movement which humans hardly can move or select for their destinations in a square area. This model often results in a non-uniform stationary node distribution and hence complicates the analysis BIB001 BIB003 BIB004 BIB002 . RWP is improved by Smooth Random Mobility Model (SRMM) that adds a temporal dependency where speed is changed incrementally in a smooth fashion BIB002 .