1736367
Distributed Channel Monitoring for Wireless Bandwidth Aggregation
Aggregating low-speed WAN links into a higher-speed logical link promises to improve data-transfer rates to collaborating communities of wireless mobile multi-homed devices. Such bandwidth aggregation systems must adapt to link dynamics as the number of links and the channel conditions vary with time due to mobility, power dissipation, and channel interference. A monitoring architecture that accurately measures the link dynamics and promptly feeds this information to the system is vital to realize significant bandwidth aggregation performance gains. We present various architectural design alternatives for such a monitoring system, and evaluate them using simulation. We show that a properly-designed monitoring system can accurately measure and quickly respond to changes in communication link performance while minimizing the control overhead.
10953963
Ad Hoc Routing with Early Unidirectionality Detection and Avoidance
This paper is motivated by the observation that current research in ad hoc networks mostly assumes a physically flat network architecture with the nodes having homogeneous characteristics, roles, and networking- and processing-capabilities (e.g., network resources, computing power, and transmission power). In real-world ad hoc networks however, node heterogeneity is inherent. New mechanisms at the network layer are required for effective and efficient utilization of such heterogeneous networks. We discuss the issues and challenges for routing protocol design in heterogeneous ad hoc networks, and focus on the problem of quickly detecting and avoiding unidirectional links. We propose a routing framework called Early Unidirectionality Detection and Avoidance (EUDA) that utilizes geographical distance and path loss between the nodes for fast detection of asymmetric and unidirectional routes. We evaluate our scheme through ns-2 simulation and compare it with existing approaches. Our results demonstrate that our techniques work well in these realistic, heterogeneous ad hoc networking environments with unidirectional links.
18581129
Selecting a routing strategy for your ad hoc network
In this paper we investigate the performance of routing strategies in ad hoc networks. An ad hoc network operates without a central entity or infrastructure, and is composed of highly mobile network hosts. In this environment, routes tend to be multihop and routing protocols are faced with host mobility and bandwidth constraints. In recent years, numerous routing protocols of different styles have been proposed. Traditional table-driven protocols (distance vector, link state), reactive on-demand protocols, and location-based protocols that use position information provided by GPS are the most commonly used strategies. Using PARSEC, we simulate protocols that represent these various routing strategies. The protocols are evaluated in different network scenarios. Relative strengths, weaknesses, and applicability to various situations of each routing protocol are studied and discussed.
933849
Scalability study of the ad hoc on-demand distance vector routing protocol
As mobile networking continues to experience increasing popularity, the need to connect large numbers of wireless devices will become more prevalent. Many recent proposals for ad hoc routing have certain characteristics that may limit their scalability to large networks. This paper examines five different combinations of modifications that may be incorporated into virtually any on-demand protocol in order to improve its scalability. The scalability of current on-demand routing protocols is evaluated through the selection of a representative from this class of protocols. The performance of the un-modified on-demand protocol is compared against that of it combined with each of the scalability modifications. Each scheme's behavior is analyzed in networks as large as 10,000 nodes through detailed simulation. Based on the observations, conclusions are drawn as to the expected scalability improvement that can be achieved by each modification.
9065684
NodeWiz: peer-to-peer resource discovery for grids
Efficient resource discovery based on dynamic attributes such as CPU utilization and available bandwidth is a crucial problem in the deployment of computing grids. Existing solutions are either centralized or unable to answer advanced resource queries (e.g., range queries) efficiently. We present the design of NodeWiz, a grid information service (CIS) that allows multi-attribute range queries to be performed efficiently in a distributed manner. This is obtained by aggregating the directory services of individual organizations in a peer-to-peer information service.
10289717
Estimating network proximity and latency
Network proximity and latency estimation is an important component in discovering and locating services and applications. With the growing number of services and service providers in the large-scale Internet, accurately estimating network proximity/latency with minimal probing overhead becomes essential for scalable deployment. Although there exist a number of network distance estimation schemes, they either rely on extensive infrastructure support, require the IP address of the potential targets, falsely cluster distant nodes, or perform poorly with even few measurement errors. We propose Netvigator, a scalable network proximity and latency estimation tool that uses information obtained from probing a small number of landmark nodes and intermediate routers (termed milestones) that are discovered en route to the landmarks, to identify the closest nodes. With very little additional probing overhead, Netvigator uses distance information to the milestones to accurately locate the closest nodes. We developed a Netvigator prototype and report our performance evaluation on PlanetLab and in the intranet of a large enterprise. Netvigator is a running service on PlanetLab as a part of HP Labs' S3 (Scalable Sensing Service).
18227774
Feature-based surface light field morphing
A surface light field is a function that gives the colors of each object point viewed from different directions. Object representation with a surface light field provides a nice structure for 3D photography. This paper presents a feature-based morphing technique for two objects equipped with surface light fields. The technique consists of geometry morphing and in-between light field mapping. Geometry morphing is accomplished by 3D mesh morphing, where we introduce a vertex merging technique to generate a simpler metamesh. In in-between light field mapping, an in-between object is rendered by extracting necessary fragments from input surface light fields. We also propose an acceleration technique for rendering an in-between object. Experimental results with real and synthetic data show natural and plausible morphing between objects with surface light fields. The proposed morphing technique can be used as an editing tool for 3D photography.
27471022
Deletion measures for generalized linear mixed effects models
Generalized linear mixed models (GLMMs) have wide applications in practice. Similar to other data analyses, the identification of influential observations that may be potential outliers is an important step beyond estimation in GLMMs. Since the pioneering work of Cook in 1977, deletion measures have been applied to many statistical models for identifying influential observations. However, as this well-known approach is based on the observed-data likelihood, it is very difficult to apply it to developing diagnostic measures for GLMMs due to the complexity of the observed-data likelihood that involves multidimensional integrals. The objective of this article is to develop diagnostic measures for identifying influential observations. Deletion measures are developed on the basis of the conditional expectation of the complete-data log-likelihood at the E-step of a stochastic approximation Markov chain Monte Carlo algorithm. Making use of by-products of the estimation to compute building blocks of the proposed diagnostic measures and activating appropriate approximations, the proposed methods require little additional computation. The performance of the methods is illustrated by an artificial example, a real example, and some simulation studies.
17617945
INSIGNIA: An IP-Based Quality of Service Framework for Mobile ad Hoc Networks
We present the design, implementation, and evaluation of INSIGNIA, an IP-based quality of service framework that supports adaptive services in mobile ad hoc networks. The framework is based on an in-band signaling and soft-state resource management approach that is well suited to supporting mobility and end-to-end quality of service in highly dynamic environments where the network topology, node connectivity, and end-to-end quality of service are time varying. Architecturally INSIGNIA is designed to support fast reservation, restoration, and end-to-end adaptation based on the inherent flexibility and robustness and scalability found in IP networks. We evaluate the framework, paying particular attention to the performance of the in-band signaling system, which helps counter time-varying network dynamics in support of the delivery of adaptive services. Our results show the benefit of our framework under diverse mobility, traffic, and channel conditions.
6107286
Efficient geographic routing in multihop wireless networks
We propose a new link metric called normalized advance (NADV) for geographic routing in multihop wireless networks. NADV selects neighbors with the optimal trade-off between proximity and link cost. Coupled with the local next hop decision in geographic routing, NADV enables an adaptive and efficient cost-aware routing strategy. Depending on the objective or message priority, applications can use the NADV framework to minimize various types of link cost.We present efficient methods for link cost estimation and perform detailed simulations in diverse scenarios. Our results show that NADV outperforms current schemes in many aspects: for example, in high noise environments with frequent packet losses, the use of NADV leads to 81% higher delivery ratio. When compared to centralized routing under certain settings, geographic routing using NADV finds paths whose cost is close to the optimum.
14142156
Out-of-Vocabulary Rejection based on Selective Attention Model
Based on a psychological selective attention theory a new algorithm is developed to provide reliable out-of-vocabulary (OOV) rejection for speech recognition systems in noisy environments. The developed attention model is based on Broadbent's ‘early filtering’ theory, and the attention adaptation process utilizes a gradient-descent error minimization algorithm with error backpropagation rule. The developed model is applied to isolated-word recognition tasks, and much higher in-vocabulary recognition rates are achieved with the same out-of-vocabulary rejection rates.