In the performance evaluation of a protocol for an ad hoc network, the protocol should be tested under realistic conditions including, but not limited to, a sensible transmission range, limited buffer space for the storage of messages, representative data traffic models, and realistic movements of the mobile users (i.e., a mobility model). This paper is a survey of mobility models that are used in the simulations of ad hoc networks. We describe several mobility models that represent mobile nodes whose movements are independent of each other (i.e., entity mobility models) and several mobility models that represent mobile nodes whose movements are dependent on each other (i.e., group mobility models). The goal of this paper is to present a number of mobility models in order to offer researchers more informed choices when they are deciding upon a mobility model to use in their performance evaluations. Lastly, we present simulation results that illustrate the importance of choosing a mobility model in the simulation of an ad hoc network protocol. Specifically, we illustrate how the performance results of an ad hoc network protocol drastically change as a result of changing the mobility model simulated.

One of the most important methods for evaluating the characteristics of ad hoc networking protocols is through the use of simulation. Simulation provides researchers with a number of significant benefits, including repeatable scenarios, isolation of parameters, and exploration of a variety of metrics. The topology and movement of the nodes in the simulation are key factors in the performance of the network protocol under study. Once the nodes have been initially distributed, the mobility model dictates the movement of the nodes within the network. Because the mobility of the nodes directly impacts the performance of the protocols, simulation results obtained with unrealistic movement models may not correctly reflect the true performance of the protocols. The majority of existing mobility models for ad hoc networks do not provide realistic movement scenarios; they are limited to random walk models without any obstacles. In this paper, we propose to create more realistic movement models through the incorporation of obstacles. These obstacles are utilized to both restrict node movement as well as wireless transmissions. In addition to the inclusion of obstacles, we construct movement paths using the Voronoi diagram of obstacle vertices. Nodes can then be randomly distributed across the paths, and can use shortest path route computations to destinations at randomly chosen obstacles. Simulation results show that the use of obstacles and pathways has a significant impact on the performance of ad hoc network protocols.

Secure communication is very important in computer networks and authentication is one of the most eminent preconditions. However, common authentication schemes are not applicable in ad hoc networks because public key infrastructures with a centralized certification authority are hard to deploy there. We propose and evaluate a security concept based on a distributed certification facility. A network is divided into clusters with one special head node each. These cluster head nodes execute administrative functions and hold shares of a network key used for certification. New nodes start to participate in the network as guests; they can only become full members with a networksigned certificate after their authenticity has been warranted by some other members. The feasibility of this concept was verified by simulation. Three different models for node mobility were used in order to include realistic scenarios as well as make the results comparable to other work. The simulation results include an evaluation of the log-on times, availability, and communication overhead.

Simulation environments are an important tool for the evaluation of new concepts in networking. The study of mobile ad hoc networks depends on understanding protocols from simulations, before these protocols are implemented in a real-world setting. To produce a real-world environment within which an ad hoc network can be formed among a set of nodes, there is a need for the development of realistic, generic and comprehensive mobility and signal propagation models. In this paper we propose the design of a mobility and signal propagation model that can be used in simulations to produce realistic network scenarios. Our model allows the placement of obstacles that restrict movement and signal propagation. Movement paths are constructed as voronoi tessellations with the corner points of these obstacles as voronoi sites. Our mobility model also introduces a signal propagation model that emulates properties of fading in the presence of obstacles. As a result, we have developed a complete environment in which network protocols can be studied on the basis of numerous performance metrics. Through simulation, we show that the proposed mobility model has a significant impact on network performance, especially when compared to other mobility models. In addition, we also observe that the performance of ad hoc network protocols is effected when different mobility scenarios are utilized. 1

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One of the most important tools in understanding the complex characteristics of disaster recovery networks is simulation. While many mobility models exist for simulating ad hoc networks, they do not realistically capture the behavior of objects in disaster scenarios. We propose a high level event- & role-based mobility paradigm in which objects’ movement patterns are caused by environmental events. The introduction of roles allows different objects to uniquely and realistically react to events. For instance some roles, such as civilian, may flee from events, whereas other roles, such as police, may be attracted to events. Furthermore, to incorporate reaction from multiple events in a realistic fashion, we propose a low-level gravity-based mobility model in which events apply forces to objects. Simulation results show that our disaster mobility paradigm coupled with our gravitational mobility model creates a network topology that differs from the popular Random Walk mobility model. This new disaster mobility model opens up the door for more realistic simulation of communication and routing protocols for disaster recovery networks.

Mobility models, or the movement patterns of nodes communicating wirelessly, play a vital role in the simulation-based evaluation of Vehicular Ad Hoc Networks (VANETs). Although recent research has developed models that better correspond to real world mobility, we still have a limited understanding of the level of the required level of mobility details for modeling and simulating VANETs. In this work, we examine a set of step-by-step enhancements to the level of details in mobility models for VANETs and evaluate the sensitivity of simulation results toward those modeling details. Through this process, we develop several new mobility models, that account for vehicular movement constraints such as traffic lights, multilane roads, and acceleration/deceleration. Using real and controlled synthetic maps, we compare our mobility models and two prior models. Our results demonstrate that the delivery ratio and packet delays in VANETs are more sensitive to the clustering effect of vehicles waiting at intersections and acceleration/deceleration of vehicles. We also found that the simulation of multiple lanes and synchronization at traffic signals have only a marginal impact on the ad hoc routing performance. Our work provides a sound starting point for further understanding and development of more realistic and accurate mobility models for VANET simulations.

Abstract. This paper describes an event dissemination algorithm that implements a topic-based publish/subscribe interaction abstraction in mobile ad-hoc networks (MANETs). Our algorithm is frugal in two senses. First, it reduces the total number of duplicates and parasite events received by the subscribers. Second, both the mobility of the publishers and the subscribers, as well as the validity periods of the events, are exploited to achieve a high level of dissemination reliability with a thrifty usage of the memory and bandwidth. Besides, our algorithm is inherently portable and does not assume any underlying routing protocol. We give simulation results of our algorithms in the two most popular mobility models: city section and random waypoint. We highlight interesting empirical lower bounds on the minimal validity period of any given event to ensure its reliable dissemination. 1

Abstract — In wireless ad hoc networks, the ability to analytically characterize the spatial distribution of terminals plays a key role in understanding fundamental network QoS measures such as throughput per source to destination pair, probability of successful transmission, connectivity, etc. Consequently, mobility models that are general enough to capture the major characteristics of a realistic movement profile, and yet are simple enough to mathematically formulate its long-run behavior, are highly desirable. In this paper, we propose a generalized random mobility model capable of capturing several mobility scenarios and give a mathematical framework for its exact analysis over one-dimensional mobility terrains. The model provides the flexibility to capture hotspots where mobiles accumulate with higher probability and spend more time. The selection process of hotspots is random and correlations between the consecutive hotspot decisions are successfully modeled. Furthermore, the times spent at the destinations can be dependent on the location of destination point, the speed of movement can be a function of distance that is being traveled, and the acceleration characteristics of vehicles can be incorporated into the model. Our solution framework formulates the model as a semi-Markov process using a special discretization technique. We provide long-run location and speed distributions by closed-form expressions for one-dimensional regions (e.g., a highway).

Abstract. This article surveys mobility patterns and mobility models for wirelss networks. Mobility patterns are classified into the following types: pedestrians, vehicles, aerial, dynamic medium, robot, and outer space motion. We present the characteristics of each and shortly mention the specific problems. We shortly present the specifics of cellular networks, mobile ad hoc networks, and sensor networks regarding mobility. Then, we present the most important mobility models from the literature. At last we give a brief discussion about the state of research regarding mobility in wireless networks. 1