Virtual infrastructure for wireless ad hoc networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (v. 2, p. 585-591) and index.One of the most significant challenges introduced by ad hoc networks is coping with the unpredictable deployment, uncertain reliability, and erratic communication exhibited by emerging wireless networks and devices. The goal of this thesis is to develop a set of algorithms that address these challenges and simplify the design of algorithms for ad hoc networks. In the first part of this thesis, I introduce the idea of virtual infrastructure, an abstraction that provides reliable and predictable components in an unreliable and unpredictable environment. This part assumes reliable communication, focusing primarily on the problems created by unpredictable motion and fault-prone devices. I introduce several types of virtual infrastructure, and present new algorithms based on the replicated-state-machine paradigm to implement these infrastructural components. In the second part of this thesis, I focus on the problem of developing virtual infrastructure for more realistic networks, in particular coping with the problem of unreliable communication. I introduce a new framework for modeling wireless networks based on the ability to detect collisions. I then present a new algorithm for implementing replicated state machines in wireless networks, and show how to use replicated state machines to implement virtual infrastructure even in an environment with unreliable communication.by Seth Gilbert.Ph.D

Virtual backbone formation in wireless ad hoc networks

We study the problem of virtual backbone formation in wireless ad hoc networks. A virtual backbone provides a hierarchical infrastructure that can be used to address important challenges in ad hoc networking such as efficient routing, multicasting/broadcasting, activity-scheduling, and energy efficiency. Given a wireless ad hoc network with symmetric links represented by a unit disk graph G = (V, E ), one way to construct this backbone is by finding a Connected Dominating Set (CDS) in G , which is a subset V' ✹ V such that for every node u, u is either in V' or has a neighbor in V' and the subgraph induced by V' is connected. In a wireless ad hoc network with asymmetric links represented by a directed graph G = (V, E ), finding such a backbone translates to constructing a Strongly Connected Dominating and Absorbent Set (SCDAS) in G . An SCDAS is a subset of nodes V' ✹ V such that every node u is either in V' or has an outgoing and an incoming neighbor in V' , and the subgraph induced by V' is strongly connected. Based on most of its applications, minimizing the size of the virtual backbone is an important objective. Therefore, we are interested in constructing CDSs and SCDASs of minimal size. We give efficient distributed algorithms with linear time and message complexities for the construction of the CDS in ad hoc networks with symmetric links. Since topology changes are quite frequent in most ad hoc networks, we propose schemes to locally maintain the CDS in the face of such changes. We also give a distributed algorithm for the construction of the SCDAS in ad hoc networks with asymmetric links. Extensive simulations show that our algorithms outperform all previously known algorithms in terms of the size of the constructed sets

A Rapid Development of Dependable Applications in Ad Hoc Mobility

Advances in wireless communication and network computing technologies make possible new kinds of applications involving transient interactions among physical components that move across a wide range of spaces, from the confines of a room to the airspace across an ocean, and require no fixed networking infrastructure to communicate with one another. Such components may come together to form ad hoc networks for the purpose of exchanging information or in order to engage in cooperative task-oriented behaviors. Ad hoc networks are assembled, reshaped and taken apart as components move in and out of communication range; all interactions are transient; computations become highly decoupled and rely on weak forms of data consistency; disconnections are frequent and unpredictable; and component behavior is sensitive to changes in location, context, quality of service, or administrative domain. Our objective is to develop an environment that will facilitate rapid development of dependable mobile applications executing over ad hoc networks. Our primary focus will be the development of coordination constructs that support transient interactions among components, specifically through the design of global virtual data structures. Operations and their effects on these data structures must be defined with respect to the current connectivity context. We intend to use formal modeling techniques to define these constructs and their operating constraints as well as providing the specification for implementing these structure. Part of this specification will involve the development of algorithms for the ad hoc environment such as leader election, termination detection, and transactions

About the Self-Stabilization of a Virtual Topology for Self-Organization in Ad Hoc Networks

International audienceAd hoc networks are spontaneous wireless networks without any wired infrastructure, composed of mobile terminals. We assume that nodes must collaborate to set up an efficient network, such a collaboration requiring a self-organization in the network. We proposed a virtual structure to organize the network: the backbone is a connected structure helping to optimize the control traffic flooding. Clusters form services area, hierarchizing the network, electing one leader per cluster. Since the ad hoc topology is volatile, the self-stabilization of the algorithms is vital. The algorithms for both the construction and the maintenance are analytically studied to prove the self-stabilization of the proposed self-organization. Thus, the virtual structure is efficient and very scalable, a local topology change impacting only locally the virtual structure. Finally , simulations investigate the behavior and the performances of the virtual structure

Virtual Router Approach For Wireless Ad Hoc Networks

Wireless networks have become increasingly popular in recent years. There are two variations of mobile wireless networks: infrastructure mobile networks and infrastructureless mobile networks. The latter are also known as mobile ad hoc network (MANET). MANETs have no fixed routers. Instead, mobile nodes function as relay nodes or routers, which discover and maintain communication connections between source nodes and destination nodes for various data transmission sessions. In other words, an MANET is a self-organizing multi-hop wireless network in which all nodes within a given geographical area participate in the routing and data forwarding process. Such networks are scalable and self-healing. They support mobile applications where an infrastructure is either not available (e.g., rescue operations and underground networks) or not desirable (e.g., harsh industrial environments). In many ad hoc networks such as vehicular networks, links among nodes change constantly and rapidly due to high node speed. Maintaining communication links of an established communication path that extends between source and destination nodes is a significant challenge in mobile ad hoc networks due to movement of the mobile nodes. In particular, such communication links are often broken under a high mobility environment. Communication links can also be broken by obstacles such as buildings in a street environment that block radio signal. In a street environment, obstacles and fast moving nodes result in a very short window of communication between nodes on different streets. Although a new communication route can be established when a break in the communication path occurs, repeatedly reestablishing new routes incurs delay and substantial overhead. To address this iv limitation, we introduce the Virtual Router abstraction in this dissertation. A virtual router is a dynamically-created logical router that is associated with a particular geographical area. Its routing functionality is provided by the physical nodes (i.e., mobile devices) currently within the geographical region served by the virtual router. These physical nodes take turns in forwarding data packets for the virtual router. In this environment, data packets are transmitted from a source node to a destination node over a series of virtual routers. Since virtual routers do not move, this scheme is much less susceptible to node mobility. There can be two virtual router approaches: Static Virtual Router (SVR) and Dynamic Virtual Router (DVR). In SVR, the virtual routers are predetermined and shared by all communication sessions over time. This scheme requires each mobile node to have a map of the virtual routers, and use a global positioning system (GPS) to determine if the node is within the geographical region of a given router. DVR is different from SVR with the following distinctions: (1) virtual routers are dynamically created for each communication sessions as needed, and deprecated after their use; (2) mobile nodes do not need to have a GPS; and (3) mobile nodes do not need to know whereabouts of the virtual routers. In this dissertation, we apply Virtual Router approach to address mobility challenges in routing data. We first propose a data routing protocol that uses SVR to overcome the extreme fast topology change in a street environment. We then propose a routing protocol that does not require node locations by adapting a DVR approach. We also explore how the Virtual Router Approach can reduce the overhead associated with initial route or location requests used by many existing routing protocols to find a destination. An initial request for a destination is expensive v because all the nodes need to be reached to locate the destination. We propose two broadcast protocols; one in an open terrain environment and the other in a street environment. Both broadcast protocols apply SVR. We provide simulation results to demonstrate the effectiveness of the proposed protocols in handling high mobility. They show Virtual Router approach can achieve several times better performance than traditional routing and broadcast approach based on physical routers (i.e., relay nodes

To mesh or not to mesh: flexible wireless indoor communication among mobile robots in industrial environments

Mobile robots such as automated guided vehicles become increasingly important in industry as they can greatly increase efficiency. For their operation such robots must rely on wireless communication, typically realized by connecting them to an existing enterprise network. In this paper we motivate that such an approach is not always economically viable or might result in performance issues. Therefore we propose a flexible and configurable mixed architecture that leverages on mesh capabilities whenever appropriate. Through experiments on a wireless testbed for a variety of scenarios, we analyse the impact of roaming, mobility and traffic separation and demonstrate the potential of our approach

Mobile Social Networking aided content dissemination in heterogeneous networks

Since more and more mobile applications are based on the proliferation of social information, the study of Mobile Social Net-works (MSNs) combines social sciences and wireless communications. Operating wireless networks more efficiently by exploiting social relationships between MSN users is an appealing but challenging option for network operators. An MSN-aided content dissemination technique is presented as a potential ex-tension of conventional cellular wireless net-works in order to satisfy growing data traffic. By allowing the MSN users to create a self-organized ad hoc network for spontaneously disseminating contents, the network operator may be able to reduce the operational costs and simultaneously achieve an improved network performance. In this paper, we first summarize the basic features of the MSN architecture, followed by a survey of the factors which may affect MSN-aided content dissemination. Using a case study, we demonstrate that one can save resources of the Base Station (BS) while substantially lowering content dissemination delay. Finally, other potential applications of MSN-aided content dissemination are introduced, and a range of future challenges are summarized