15776548
Cross-layer flow control in lightly-loaded multi-hop ad hoc networks
The throughput in multi-hop ad hoc networks (MANETs) is highly dependent on the sending rate and the route length from the source node to the destination. Sending packets at the optimal rate for a given route length maximizes throughput in the network, whereas slightly increasing the sending rate over the optimal value may decrease throughput by up to 55%. This paper presents a novel cross-layer technique for flow control in lightly-loaded MANETs. The technique allows applications to send packets at the rate that maximizes throughput for a given route length. To achieve this, the routing layer notifies interested applications about routing changes, and the applications adaptively modify their sending rates based on the new route length to the destination. In static and mobile networks, this technique outperforms UDP-based flows with a fixed sending rate and doubles the throughput of TCP for networks with up to 2 concurrent flows.
584351
Efficient peer-to-peer data dissemination in mobile ad-hoc networks
Without infrastructural support from base stations, mobile nodes in an ad hoc network communicate with each other in a peer-to-peer fashion. This poses a challenge in data dissemination among the mobile peers, each having limited transmission range and unpredictable mobility. We first propose a novel mobility model to characterize user mobility in a civilian environment, such as a college campus. We then propose the application of Tornado coding as an efficient solution to the challenge of ad hoc peer-to-peer data dissemination. A mobile node is able to download coded file segments from different peers-at different times and in different locations. When it receives sufficient segments, it will be able to re-construct the original file. Although Tornado coding itself is not new, we for the first time propose its application to mobile ad hoc data dissemination. Furthermore, we show how Tornado coding parameters affect the performance of peer-to-peer data dissemination.
7321726
A gateway-assisted approach toward QoS adaptations
We present a gateway-assisted QoS adaptation framework which satisfies high-level QoS application guarantees. We validate this framework via a distributed tracking system and show provisioning of critical QoS guarantees despite the best effort underlying resource management.
14174120
Overlay Multicast with Inferred Link Capacity Correlations
We model the overlay using linear capacity constraints, which accurately and succinctly capture overlay link correlations. We show that finding a maximum-bandwidth multicast tree in an overlay with LCC is NP-complete and propose an efficient distributed heuristics algorithm.
8043231
QoS-Aware Adaptive Services in Mobile Ad-Hoc Networks
Ad-hoc wireless networks consist of mobile nodes interconnected by multi-hop wireless paths. Unlike conventional wireless networks, ad-hoc networks have no fixed network infrastructure or administrative support. Because of the dynamic nature of the network topology and limited bandwidth of wireless channels, Quality-of-Service (QoS) provisioning is an inherently complex and difficult issue. In this paper, we propose a fully distributed and adaptive algorithm to provide statistical QoS guarantees with respect to accessibility of services in an ad-hoc network. In this algorithm, we focus on the optimization of a new QoS parameter of interest, service efficiency, while keeping protocol overheads to the minimum. To achieve this goal, we first theoretically derive the lower and upper bounds of service efficiency based on a novel model for group mobility, followed by extensive simulation results to verify the effectiveness of our algorithm.
7456112
Efficient and guaranteed service coverage in partitionable mobile ad-hoc networks
In wireless ad-hoc networks, the network topology changes dynamically and unpredictably due to node mobility. Such topological dynamics are further exacerbated by the natural grouping behavior in the mobile user's movement, which leads to frequent network partitioning. Network partitioning poses significant challenges to the provisioning of centralized services in ad-hoc networks, since partitioning disconnects many mobile users from the central server. We propose a collection of novel run-time algorithms that adaptively ensure the centralized service is available to all mobile nodes during network partitioning, while minimizing the number of servers required. The network-wide service coverage is achieved by partition prediction and service replication on the servers, and assisted by distributed service selection on regular mobile nodes. Simulation results show that our algorithm efficiently achieves guaranteed service coverage to all nodes. To the best of our knowledge, there have been no similar approaches that use partition prediction to provision centralized services adaptively in partitionable mobile ad-hoc networks.
71018
Experimental Study on Representing Units in Chinese Text Categorization
This paper is a comparative study on representing units in Chinese text categorization. Several kinds of representing units, including byte 3-gram, Chinese character, Chinese word, and Chinese word with part of speech tag, were investigated. Empirical evidence shows that when the size of training data is large enough, representations of higher-level or with larger feature spaces result in better performance than those of lower level or with smaller feature spaces, whereas when the training data is limited the conclusion may be the reverse. In general, representations of higher-level or with larger feature spaces need more training data to reach the best performance. But, as to a specific representation, the size of training data and the categorization performance are not always positively correlated.
46149042
Data reconciliation for real-time optimization of an industrial coke-oven-gas purification process
Online optimization is more and more used in the chemical industry to run a process near its optimum operating condition by providing real-time computed optimal set-points to the distributed control system. Process measurements are necessary for these applications to determine the actual state of the process and to increase the accuracy of the model with parameter estimation techniques. However, these measurements usually contain random as well as gross errors which have to be identified and eliminated before the measurements are used for online optimization. In this contribution, a data reconciliation approach was integrated into an online optimization framework for the ammonia hydrogen sulfide circulation scrubbing, a common industrial coke-oven-gas purification process. We used a rigorous rate-based model to describe this reactive absorption and desorption process. To increase the accuracy of the model, we estimated several process parameters using a sequential parameter estimation approach. Data reconciliation was performed based on simple component balances to achieve model-consistent data and to identify measurement biases. The model was then validated online on a pilot plant by connecting the estimation package through the process control system. Based on the online measured data, operating cost minimization was carried out and the computed optimal set-points realized real-time. A satisfactory agreement between measured data and optimization was achieved.
5295208
Bit rate reduction of H.264/AVC video coding for mobile applications
The increasing use of mobile applications requires higher compression efficiency for video coding. However, in mobile applications, the capability of the processor is limited and the channel is unreliable. Since the emerging H.264/AVC video coding standard provides superior compression performance compared to all the existing video coding standards, many research efforts concentrate on the compression efficiency of intra-frame coding in H.264/AVC. In this paper, we propose a novel algorithm to reduce the bit rate compressed by H.264/AVC intra-frame coding. We focus on the method to code the intra-frame prediction modes. Our proposed method significantly reduces the bits used to code the modes and do not change the syntax of the bit stream. Experimental results demonstrate it is effective and efficient
12626074
Dynamic routing and wavelength assignment in the presence of wavelength conversion for all-optical networks
Blocking probability has been one of the key performance indexes in the design of wavelength-routed all-optical WDM networks. Existing research has demonstrated that an effective Routing and Wavelength Assignment (RWA) algorithm and wavelength conversion are two primary vehicles for improving the blocking performance. However, these two issues have largely been investigated separately; in particular the existing RWA algorithms have seldom considered the presence of wavelength conversion. In this paper, we firstly demonstrate that the existing dynamic RWA algorithms do not work well in the presence of wavelength conversion as they usually only take into account the current traffic, and do not explicitly consider the route lengths. We then propose a weighted least-congestion routing and first-fit wavelength assignment (WLCR-FF) algorithm that considers both the current traffic load and the route lengths jointly. We further introduce an analytical model that can evaluate the blocking performance for WLCR algorithm. We carry out extensive numerical studies over typical topologies including ring, mesh-torus, and the 14-node NSFNET; and compare the performance of WLCR-FF with a wide variety of existing routing algorithms including static routing, fixed-alternate routing and least-loaded routing. The results conclusively demonstrate that the proposed WLCR-FF algorithm can achieve much better blocking performance in the presence of sparse or/and full wavelength conversion.
2962872
Finite element analysis of a class of stress-free martensitic microstructures
This work is concerned with the finite element approximation of a class of stress-free martensitic microstructures modeled by multi-well energy minimization. Finite element energy-minimizing sequences are first constructed to obtain bounds on the minimum energy over all admissible finite element deformations. A series of error estimates are then derived for finite element energy minimizers.