6110501
A backoff copying scheme for contention resolution in wireless sensor networks
This paper aims at improving the throughput and fairness of the wireless sensor networks (WSN). Due to the disproportionate larger number of packets accumulated in the sensors that are closer to the base station, it's necessary to have a better contention resolution scheme to improve the throughput and fairness in WSN. In this paper, we propose a new mechanism named BCCR (Backoff Copying for Contention Resolution), which is targeted to a system-wide proportional fairness in WSN. The new method is designed particularly for a many-to-one data collection tree structure, employing a mechanism that translates a fairness model into contention resolution. In BCCR, the size of the backoff window is dynamically adjusted to the channel allocation rate of the flow sent by the sensors. And the backoff algorithm does not focus on each node, but focus on each region which is divided according to the traffic flow contention. In every contention region, sensor nodes will share the same backoff window by a copying scheme. With extensive simulations and testbed experiments, we show that BCCR can achieve the expected fairness and throughput increase over the traditional CSMA, especially when the network is congested.
18306747
Visualizing simulation and testbed of wireless sensor networks with NetTopo
In this paper, we present an integrated framework called NetTopo for providing both simulation and visualization functions to assist the investigation of algorithms in WSNs. NetTopo provides a common virtual WSN for the purpose of interaction between sensor devices and simulated virtual nodes. Two case studies are described to prove the effectiveness of NetTopo.
17681650
Cross-Layer Optimized Data Gathering in Wireless Multimedia Sensor Networks
Using multimedia sensor nodes can enhance the capability of wireless sensor networks (WSNs) for event description. In some scenarios, e.g., an erupting volcano, the WSNs are not deployed to work for long time. Instead, the WSNs aim to deliver continuous and reliable multimedia data as much as possible within an expected lifetime. In this paper, we focus on the efficient multimedia data gathering in WSNs within an expected lifetime. A distributed transmission Radius and data generation Rate Adjustment (RRA) scheme is proposed based on a cross-layer design, considering the interaction among physical, network and transport layers. Simulation results show that the proposed RRA strategy can effectively enhance the data gathering performance in wireless multimedia sensor networks (WMSNs) by dynamically adjusting the transmission radius of sensor nodes and the data generation rate of source nodes.
21998790
NetTopo: Beyond Simulator and Visualizer for Wireless Sensor Networks
Deploying real WSN testbed provides a realistic testing environment, and allows users to get more accurate test results. However, deploying real testbed is highly constrained by the available budget when the test needs a large scale WSN environment. By leveraging the advantages of both simulators and real testbed, an approach that integrates simulation environment and testbed can effectively solve both scalability and accuracy issues. In this paper, we present NetTopo for providing both simulation and visualization functions to assist the investigation of algorithms in WSNs. Two case studies are described to prove the effectiveness of NetTopo.
15162154
Trust Mechanism in Distributed Access Control Model of P2P Networks
Peer-to-peer network technologies have gained popularity without the need for centralized servers. With the consistent development of the network, the existing techniques about access control could not resolve the security issues in P2P networks perfectly. How to realize the trust mechanism in access control system is an important subject of P2P security research. In this paper, we analyze the lack of trust mechanism in the existing access control models, and present a recommendation trust model based on reputation. We introduce the related concepts in the trust model and explain the mechanism of trust. Then, a protocol of trust query is designed and calculations about trust are given. At last, we validate the availability of the trust model, and applied it in the existing access control model. The combining of trust mechanism and access control technologies makes the P2P networks securer.
37911723
The Research of Complex System Modeling Based on Fractal Conception
41889531
Research on Pairwise Key Establishment Model and Algorithm for Sensor Networks
Security schemes of pairwise key establishment, which enable sensors to communicate with each other securely, play a fundamental role in research on security issue in wireless sensor networks. A new kind of pairwise key pre-distribution model for sensor networks is proposed. And in addition, based on which, an efficient dynamic key path establishment algorithm is designed. Theoretic analysis and experimental figures show that the new algorithm has better performance than those previous related works.
14777107
Cooperative OFDM for energy-efficient wireless sensor networks
This paper presents a new energy-efficient cooperative sensor network scheme. Cooperative nodes shift the carrier frequency of the source node, and the destination node receives the signal from the source node and the cooperative nodes as a standard orthogonal frequency division multiplexing (OFDM) receiver. The maximal ratio combining (MRC) approach is applied to achieve full diversity with low complexity. The proposed scheme is scalable with respect to the number of nodes and is robust to time synchronization. A clustered network topology and cooperation protocol are proposed to realize multi-hop long haul signal transmission. The effect of the cluster scale is studied thoroughly to obtain the optimal size of clusters subject to the cooperation overhead. Simulation results show that the proposed cooperation scheme can consistently reduce the transmission power with the increase of cooperation scale. However, there is an optimal cluster scale where a good tradeoff between the diversity gain and cooperation cost can be established to minimize the total power consumption of the whole network.
8366599
Achieving both high precision and high recall in near-duplicate detection
To find near-duplicate documents, fingerprint-based paradigms such as Broder's shingling and Charikar's simhash algorithms have been recognized as effective approaches and are considered the state-of-the-art. Nevertheless, we see two aspects of these approaches which may be improved. First, high score under these algorithms' similarity measurement implies high probability of similarity between documents, which is different from high similarity of the documents. But how similar two documents are is what we really need to know. Second, there has to be a tradeoff between hash-code length and hash-code multiplicity in fingerprint paradigms, which makes it hard to maintain a satisfactory recall level while improving precision.
 In this paper our contributions are two-folded. First, we propose a framework for implementing the longest common subsequence (LCS) as a similarity measurement in reasonable computing time, which leads to both high precision and recall. Second, we present an algorithm to get a trustable partition from the LCS to reduce the negative impact from templates used in web page design. A comprehensive experiment was conducted to evaluate our method in terms of its effectiveness, efficiency, and quality of result. More specifically, the method has been successfully used to partition a set of 430 million web pages into 68 million subsets of similar pages, which demonstrates its effectiveness. For quality, we compared our method with simhash and a Cosine-based method through a sampling process (Cosine is compared to LCS as an alternative similarity measurement). The result showed that our algorithm reached an overall precision of 0.95 while simhash was 0.71 and Cosine was 0.82. At the same time our method obtains 1.86 times as much recall as simhash and 1.56 times as much recall as Cosine. Comparison experiment was also done for documents in the same web sites. For that, our algorithm, simhash and Cosine find almost the same number of true-positives at a precision of 0.91, 0.50 and 0.63 respectively. In terms of efficiency, our algorithm takes 118 hours to process the whole archive of 430 million topic-type pages on a cluster of six Linux boxes, at the same time the processing time of simhash and Cosine is 94 hours and 68 hours respectively. When considering the need of word segmentation for languages such as Chinese, the processing time of Cosine should be multiplied and in our experiment it is 602 hours.