Teresa A. Dahlberg

Providing fault tolerance in wireless access networks

Research and development on network survivability has largely focused on public switched telecommunications networks and high-speed data networks with little attention on the survivability of wireless access networks supporting cellular and PCS communications. This article discusses the effects of failures and survivability issues in PCS networks with emphasis on the unique difficulties presented by user mobility and the wireless channel environment. A simulation model to study a variety of failure scenarios on a PCS network is described, and the results show that user mobility significantly worsens network performance after failures, as disconnected users move among adjacent cells and attempt to reconnect to the network. Thus, survivability strategies must be designed to contend with spatial as well as temporal network behavior. A multilayer framework for the study of PCS network survivability is presented. Metrics for quantifying network survivability are identified at each layer. Possible survivability strategies and restoration techniques for each layer in the framework are also discussed.

Performance Evaluation of Energy Efficient Ad Hoc Routing Protocols

Energy aware routing protocols are consistently cited as efficient solutions for ad hoc and sensor networks routing and data management. However, there is not a consistent approach to define the energy related cost metrics that are used to guide the routing protocol performance. This paper provides a survey and analysis of energy related metrics used for ad hoc routing. First, the most common energy efficient routing protocols are classified into four categories based on the energy cost metrics employed. Then, the results of our simulation-based analysis are presented. We conducted a complete set of simulations to compare and contrast the performance of various energy-related metrics. Our analysis provides a comparison of the performance of energy cost metrics used within AODV-based ad hoc routing protocols.

PCS network survivability

Research and development on the survivability of networks has largely focused on public switched telecommunications networks and high speed data networks with little attention on the survivability of wireless access networks supporting cellular and PCS communications. This paper provides an overview of the survivability issues in PCS networks with emphasis on the unique difficulties presented by user mobility and the wireless channel environment. A multi-layer framework for the study of PCS network survivability is proposed. Metrics for quantifying network survivability are identified at each layer. It is shown that user mobility significantly worsens the network performance after even small failures, as disconnected users move among adjacent cells and attempt to reconnect to the network. Thus survivability strategies must be designed to contend with spatial as well as temporal network behavior. Possible survivability strategies and restoration techniques for each layer in the framework are also discussed.

Survivable load sharing protocols: a simulation study

The development of robust, survivable wireless access networks requires that the performance of network architectures and protocols be studied under normal as well as faulty conditions where consideration is given to faults occurring within the network as well as within the physical environment. User location, mobility, and usage patterns and the quality of the received radio signal are impacted by terrain, man-made structures, population distribution, and the existing transportation system. The work presented herein has two thrusts. One, we propose the use of overlapping coverage areas and dynamic load balancing as a means to increase network survivability by providing mobiles with multiple access points to the fixed infrastructure. Two, we describe our simulation approach to survivability analysis which combines empirical spatial information, network models, and fault models for more realistic analysis of real service areas. We use our simulation approach to compare the survivability of our load balancing protocols to a reference scheme within two diverse geographic regions. We view survivability as a cost-performance tradeoff using handover activity as a cost metric and blocking probabilities as performance metrics. Our results illustrate this tradeoff for the protocols studied and demonstrate the extent to which the physical environment and faults therein affect the conclusions that are drawn.

Energy-efficient topology control for three-dimensional sensor networks

Topology control in sensor networks has been heavily studied recently. Different geometric topologies were proposed to be the underlying network topologies to achieve the sparseness of the communication networks or to guarantee the package delivery of specific routing methods. However, most of the proposed topology control algorithms were only applied to Two-Dimensional (2D) networks where all sensor nodes are distributed in a 2D plane. In practice, the sensor networks are often deployed in 3D space, such as sensor nodes in a forest. This paper seeks to investigate efficient topology control protocols for 3D sensor networks. In our new protocols, we extend several 2D geometric topologies to 3D case, and propose some new 3D Yao-based topologies for sensor networks. We also prove several properties (e.g. bounded degree and constant power stretch factor) for them in 3D space. The simulation results confirm our theoretical proofs for these proposed 3D topologies.

LEARN: Localized Energy Aware Restricted Neighborhood Routing for Ad Hoc Networks

In this paper, we address the problem of energy efficient localized routing in wireless ad hoc networks. Numerous energy aware routing protocols were proposed to seek the power efficiency of routes. Among them, several geographical localized routing protocols were proposed to help making smarter routing decision using only local information and reduce the routing overhead. However, most of the proposed localized routing methods cannot theoretically guarantee the power efficiency of their routes. In this paper, we give the first localized routing algorithm, called localized energy aware restricted neighborhood routing (LEARN), which can guarantee the power efficiency of its route asymptotically almost sure. Given destination node t, an intermediate node v will only select a certain neighbor v such that < vut les alpha for a parameter alpha < pi/3 in our LEARN method. We theoretically prove that for a network, formed by nodes that are produced by a Poisson distribution with rate n over a compact and convex region O with unit area, when the transmission range rn = radicbetalnl/pin for some beta > pi/alpha, our LEARN routing protocol will find the route for any pair of nodes asymptotically almost sure. When the transmission range rn = radicbetalnl/pin for some beta < pi/alpha, the LEARN routing protocol will not be able to find the route for any pair of nodes asymptotically almost sure. We also conducted simulations to study the performance of LEARN and compare it with a typical localized routing protocol (GPSR) and a global ad hoc routing protocol (DSR)

The STARS Alliance: Viable Strategies for Broadening Participation in Computing

The Students and Technology in Academia, Research, and Service (STARS) Alliance is a nationally-connected system of regional partnerships among higher education, K-12 schools, industry and the community with a mission to broaden the participation of women, under-represented minorities and persons with disabilities in computing (BPC). Each regional partnership is led by a STARS member college or university with partners such as local chapters of the Girl Scouts, the Black Data Processors Association, public libraries, Citizen Schools, and companies that employ computing graduates. STARS goals include retaining and graduating undergraduates and recruiting and bridging undergraduates into graduate programs. The alliance works toward these goals through activities that advance the central values of Technical Excellence, Leadership, Community, and Service and Civic Engagement. In particular, all STARS college and university members implement the STARS Leadership Corps (SLC), an innovative model for enveloping a diverse set of BPC practices within a common framework for implementation within multiple organizations, common assessment, and sustainability through curricula integration. Herein, we describe the SLC model and its implementation in the STARS schools, including details of an SLC service-learning course that has been adopted by eight STARS schools. We report the results of our three-year study of the SLC in the 20 STARS schools. Our study found a positive effect of participation in the SLC on important student success variables, including self-efficacy, perceived social relevance of computing, grade point average, and commitment to remain in computing. Results indicate that the SLC model is effective for students under-represented in computing, as well as for those not from under-represented groups.

Self-organizing fault-tolerant topology control in large-scale three-dimensional wireless networks

Topology control protocol aims to efficiently adjust the network topology of wireless networks in a self-adaptive fashion to improve the performance and scalability of networks. This is especially essential to large-scale multihop wireless networks (e.g., wireless sensor networks). Fault-tolerant topology control has been studied recently. In order to achieve both sparseness (i.e., the number of links is linear with the number of nodes) and fault tolerance (i.e., can survive certain level of node/link failures), different geometric topologies were proposed and used as the underlying network topologies for wireless networks. However, most of the existing topology control algorithms can only be applied to two-dimensional (2D) networks where all nodes are distributed in a 2D plane. In practice, wireless networks may be deployed in three-dimensional (3D) space, such as under water wireless sensor networks in ocean or mobile ad hoc networks among space shuttles in space. This article seeks to investigate self-organizing fault-tolerant topology control protocols for large-scale 3D wireless networks. Our new protocols not only guarantee k-connectivity of the network, but also ensure the bounded node degree and constant power stretch factor even under k−1 node failures. All of our proposed protocols are localized algorithms, which only use one-hop neighbor information and constant messages with small time complexity. Thus, it is easy to update the topology efficiently and self-adaptively for large-scale dynamic networks. Our simulation confirms our theoretical proofs for all proposed 3D topologies.

Energy-Efficient Localized Routing in Random Multihop Wireless Networks

A number of energy-aware routing protocols were proposed to seek the energy efficiency of routes in multihop wireless networks. Among them, several geographical localized routing protocols were proposed to help making smarter routing decision using only local information and reduce the routing overhead. However, all proposed localized routing methods cannot guarantee the energy efficiency of their routes. In this paper, we first give a simple localized routing algorithm, called Localized Energy-Aware Restricted Neighborhood routing (LEARN), which can guarantee the energy efficiency of its route if it can find the route successfully. We then theoretically study its critical transmission radius in random networks which can guarantee that LEARN routing finds a route for any source and destination pairs asymptotically almost surely. We also extend the proposed routing into three-dimensional (3D) networks and derive its critical transmission radius in 3D random networks. Simulation results confirm our theoretical analysis of LEARN routing and demonstrate its energy efficiency in large scale random networks.

Efficient Fault Tolerant Topology Control for Three-Dimensional Wireless Networks

Fault tolerant topology control in wireless networks has been studied recently. In order to achieve both sparseness (i.e., the number of links is linear with the number of nodes) and fault tolerance (i.e., can survive certain level of node/link failures), different geometric topologies were proposed and used as the underlying network topologies for wireless networks. However, most of the existing topology control algorithms can only be applied to 2-dimensional (2D) networks where all nodes are distributed in a 2D plane. In practice, wireless networks may be deployed in 3-dimensional (3D) space, such as underwater wireless sensor networks in ocean or ad hoc networks in space. This paper seeks to investigate efficient fault tolerant topology control protocols for 3D wireless networks. Our new protocols not only guarantee the kappa-connectivity of the network, but also ensure the bounded node degree and constant power stretch factor. All of our proposed protocols are localized algorithms, which only use one-hop neighbor information and constant messages with small time complexity. Our simulation confirms our theoretical proofs for all proposed 3D topologies.