7 research outputs found

    NASA Tech Briefs, June 2001

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    Topics covered include: Sensors; Electronic Components and Systems; Software Engineering; Materials; Manufacturing/Fabrication; physical Sciences; Information Sciences

    Networking And Security Solutions For Vanet Initial Deployment Stage

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    Vehicular ad hoc network (VANET) is a special case of mobile networks, where vehicles equipped with computing/communicating devices (called smart vehicles ) are the mobile wireless nodes. However, the movement pattern of these mobile wireless nodes is no more random, as in case of mobile networks, rather it is restricted to roads and streets. Vehicular networks have hybrid architecture; it is a combination of both infrastructure and infrastructure-less architectures. The direct vehicle to vehicle (V2V) communication is infrastructure-less or ad hoc in nature. Here the vehicles traveling within communication range of each other form an ad hoc network. On the other hand, the vehicle to infrastructure (V2I) communication has infrastructure architecture where vehicles connect to access points deployed along roads. These access points are known as road side units (RSUs) and vehicles communicate with other vehicles/wired nodes through these RSUs. To provide various services to vehicles, RSUs are generally connected to each other and to the Internet. The direct RSU to RSU communication is also referred as I2I communication. The success of VANET depends on the existence of pervasive roadside infrastructure and sufficient number of smart vehicles. Most VANET applications and services are based on either one or both of these requirements. A fully matured VANET will have pervasive roadside network and enough vehicle density to enable VANET applications. However, the initial deployment stage of VANET will be characterized by the lack of pervasive roadside infrastructure and low market penetration of smart vehicles. It will be economically infeasible to initially install a pervasive and fully networked iv roadside infrastructure, which could result in the failure of applications and services that depend on V2I or I2I communications. Further, low market penetration means there are insufficient number of smart vehicles to enable V2V communication, which could result in failure of services and applications that depend on V2V communications. Non-availability of pervasive connectivity to certification authorities and dynamic locations of each vehicle will make it difficult and expensive to implement security solutions that are based on some central certificate management authority. Nonavailability of pervasive connectivity will also affect the backend connectivity of vehicles to the Internet or the rest of the world. Due to economic considerations, the installation of roadside infrastructure will take a long time and will be incremental thus resulting in a heterogeneous infrastructure with non-consistent capabilities. Similarly, smart vehicles will also have varying degree of capabilities. This will result in failure of applications and services that have very strict requirements on V2I or V2V communications. We have proposed several solutions to overcome the challenges described above that will be faced during the initial deployment stage of VANET. Specifically, we have proposed: A VANET architecture that can provide services with limited number of heterogeneous roadside units and smart vehicles with varying capabilities. A backend connectivity solution that provides connectivity between the Internet and smart vehicles without requiring pervasive roadside infrastructure or large number of smart vehicles. A security architecture that does not depend on pervasive roadside infrastructure or a fully connected V2V network and fulfills all the security requirements. v Optimization solutions for placement of a limited number of RSUs within a given area to provide best possible service to smart vehicles. The optimal placement solutions cover both urban areas and highways environment

    Dynamic power allocation and routing for satellite and wireless networks with time varying channels

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, February 2004.Includes bibliographical references (p. 283-295).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Satellite and wireless networks operate over time varying channels that depend on attenuation conditions, power allocation decisions, and inter-channel interference. In order to reliably integrate these systems into a high speed data network and meet the increasing demand for high throughput and low delay, it is necessary to develop efficient network layer strategies that fully utilize the physical layer capabilities of each network element. In this thesis, we develop the notion of network layer capacity and describe capacity achieving power allocation and routing algorithms for general networks with wireless links and adaptive transmission rates. Fundamental issues of delay, throughput optimality, fairness, implementation complexity, and robustness to time varying channel conditions and changing user demands are discussed. Analysis is performed at the packet level and fully considers the queueing dynamics in systems with arbitrary, potentially bursty, arrival processes. Applications of this research are examined for the specific cases of satellite networks and ad-hoc wireless networks. Indeed, in Chapter 3 we consider a multi-beam satellite downlink and develop a dynamic power allocation algorithm that allocates power to each link in reaction to queue backlog and current channel conditions. The algorithm operates without knowledge of the arriving traffic or channel statistics, and is shown to achieve maximum throughput while maintaining average delay guarantees. At the end of Chapter 4, a crosslinked collection of such satellites is considered and a satellite separation principle is developed, demonstrating that joint optimal control can be implemented with separate algorithms for the downlinks and crosslinks.(cont.) Ad-hoc wireless networks are given special attention in Chapter 6. A simple cell- partitioned model for a mobile ad-hoc network with N users is constructed, and exact expressions for capacity and delay are derived. End-to-end delay is shown to be O(N), and hence grows large as the size of the network is increased. To reduce delay, a transmission protocol which sends redundant packet information over multiple paths is developed and shown to provide O(vN) delay at the cost of reducing throughput. A fundamental rate- delay tradeoff curve is established, and the given protocols for achieving O(N) and O(vN) delay are shown to operate on distinct boundary points of this curve. In Chapters 4 and 5 we consider optimal control for a general time-varying network. A cross-layer strategy is developed that stabilizes the network whenever possible, and makes fair decisions about which data to serve when inputs exceed capacity. The strategy is decoupled into separate algorithms for dynamic flow control, power allocation, and routing, and allows for each user to make greedy decisions independent of the actions of others. The combined strategy is shown to yield data rates that are arbitrarily close to the optimally fair operating point that is achieved when all network controllers are coordinated and have perfect knowledge of future events. The cost of approaching this fair operating point is an end-to-end delay increase for data that is served by the network.by Michael J. Neely.Ph.D

    Mobile Ad-Hoc Networks

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    Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks

    A hierarchical cooperation formation model for downlink data transmission in mobile infostation networks

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    Mobile infostation network is proposed as a new network paradigm to provide users with wireless data services, and a good tradeoff between the connectivity requirement and economic investment can be achieved. Mobile infostation network can offload delay-tolerant traffic from cellular network leaving more resource for mobile real-time applications. Under the mobile infostation network architecture, content distribution is achieved by exploiting the opportunistic contact among mobile users and infostations. Focusing on such a network scenario, we find that the cooperation among infostations and mobile users can improve the network performance in term of the expected delay of content distribution experienced by the users. More interestingly, jointly taking both levels of cooperation (i.e., among infostations and among mobile users) into account may achieve even better improvement, which inspires us to propose a hierarchical cooperation formation model to analyze and analyze the two-level cooperation in mobile infostation networks. To obtain the stable structure of the two-level cooperation, an implementable distributed algorithm is proposed. The hierarchical cooperation formation model can also provide some insight into other network scenarios, where cooperation is needed to improve the network performance

    Game-theoretic modeling for resource allocation in relay-based wireless networks

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    Game theory, originally invented to investigate the complex behavior in economics, has lent itself to a plethora of areas such as politics, biology, sociology and computer science nowadays. With its effectiveness in modeling the complicated behavior among different players, it is envisioned that it will play a significant role in the field of wireless communications and networking. In this dissertation, the author focuses on investigating some challenging resource allocation problems in relay-based wireless networks, a special type of wireless networks in presence of relays. To properly model the mathematical relationship between different network components and achieve a stable state where all components are satisfied with the outcome, different game-theoretic models are tailored to cope with different network scenarios. The specific issues the author addresses in this dissertation are summed up as follows. Firstly, the problem of price competition between different service providers (as owners of the relays) in wireless relay networks in presence of mobile users is considered. The payoff of a service provider is defined to be a function of both the relay price and the frequency that the relays are selected. To tackle the problem, the author designs a hierarchical framework via applying a Stackelberg-game model, where dynamic relay selection for mobile users and price competition for service providers are jointly taken into consideration. At the lower level, the author investigates the relay selection problem for the mobile users under given relay prices. It is formulated as a Markov decision process (MDP) problem with the objective to minimize the mobile user’s long-term average cost, and to be solved by applying the linear programming (LP) technique. At the upper level, the author studies the game of setting relay prices for the service providers, with the knowledgement that the mobile users will make relay selections based on their given prices. Nash equilibrium is obtained as the solution. The obtained results can help to provide a guidance for service providers to compete for providing relay services. Secondly, the author investigates the problem of power allocation for secondary users (SUs) in cognitive relay networks, where the SUs are involved as cooperative relays in a primary user’s (PU) communication. Opportunistic channel access scheme is considered, which motivates the SUs to use some relay power to speed up the PU’s transmissions. Consequently, the PU’s buffer will be depleted faster, resulting in more transmission opportunities for the SUs. Nonetheless, due to the energy limitation, less power can be used for an SU’s own transmissions if too much power is consumed on relaying. To address this tradeoff, the author designs power allocation strategies for both single-SU and multiple-SU cases. The former is formulated as a utility maximization problem, while the latter is modeled as a non-cooperative game. The existence and uniqueness of the Nash equilibrium (NE) are proved, indicating that a stable network state can be achieved where no SU can benefit more by unilaterally changing its power allocation strategy when the other SUs keep their strategies unaltered. Thirdly, the author studies the problem of cooperation formation for downlink data transmission in mobile infostation networks, where content distribution is achieved by exploiting the opportunistic contact among mobile users and infostations. Focusing on such a network scenario, the author discovers that the cooperation among infostations and mobile users can improve the network performance in term of the expected delay of content distribution. More interestingly, jointly taking both cooperation among infostations and that among mobile users into account may achieve even better improvement in performance, which inspires the author to propose a hierarchical cooperation formation model to analyze the bi-level cooperation. Coalitional formation game model and network formation game model are properly applied to obtain the stable structure of the bi-level cooperation, and an implementable distributed algorithm is proposed. Through extensive numerical experiments, the proposed algorithm is shown to be highly effective in obtaining the stable hierarchical cooperation structure.Finally, the problem of content delivery in relay-based publish-subscribe (pub-sub) networks is discussed. For the sake of optimizing the content delivery process from the content provider (CP) to the subscribers via relays in between, the CP plays a vital role in the strategy design. Modeling the pub-sub network using a tree-structured topology, tandem queueing model and absorbing Markov chain model can be applied to derive the quality-of-service (QoS) received by the subscribers (in term of the delivery ratio within deadline). It is observed that the content delivery problem has two major characteristics: (1) the CP always has the capability to control the content delivery process and is pursuing the maximum profit by strategically designing the “rights” and “obligation” items for the subscribers; (2) the subscribers are also self-interested so that they will attempt to achieve the highest benefits of themselves, however, their actions are constrained by the possible choices provided by the CP. Based on the above problem characteristics, contract theory is adopted to reach an economically optimal solution. The numerical results verify the effectiveness of the contract-theoretic approach in maximizing the CP’s profit, and the capability to ensure the satisfaction of the heterogeneous subscribers.DOCTOR OF PHILOSOPHY (SCE
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