Tsinghua Science and Technology



    2013年06期 v.18 1-4页 [查看摘要][在线阅读][下载 58K]
    [下载次数:8 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:18 ]
  • A Buffer Management Scheme for Packet Queues in MANET

    Muhammad Aamir;Mustafa A.Zaidi;

    We introduce a new scheme of buffer management to handle packet queues in Mobile Ad hoc Networks(MANETs)for fixed and mobile nodes.In this scheme,we try to achieve efficient queuing in the buffer of a centrally communicating MANET node through an active queue management strategy by assigning dynamic buffer space to all neighboring nodes in proportion to the number of packets received from neighbors and hence controlling packet drop probabilities.Our simulation study reveals that the proposed scheme is a way to improve the buffer management for packet queues in MANET nodes in terms of packet loss ratio,transmission efficiency,and some other important system parameters.

    2013年06期 v.18 543-553页 [查看摘要][在线阅读][下载 1616K]
    [下载次数:44 ] |[网刊下载次数:0 ] |[引用频次:2 ] |[阅读次数:24 ]
  • Integrating a Market-Based Model in Trust-Based Service Systems

    Suronapee Phoomvuthisarn;Yan Liu;Liming Zhu;Ross Jeffery;

    The reputation-based trust mechanism is a way to assess the trustworthiness of offered services,based on the feedback obtained from their users.In the absence of appropriate safeguards,service users can still manipulate this feedback.Auction mechanisms have already addressed the problem of manipulation by markettrading participants.When auction mechanisms are applied to trust systems,their interaction with the trust systems and associated overhead need to be quantitatively evaluated.This paper proposes two distributed architectures based on centralized and hybrid computing for integrating an auction mechanism with the trust systems.The empirical evaluation demonstrates how the architectures help to discourage users from giving untruthful feedback and reduce the overhead costs of the auction mechanisms.

    2013年06期 v.18 554-567页 [查看摘要][在线阅读][下载 3140K]
    [下载次数:33 ] |[网刊下载次数:0 ] |[引用频次:1 ] |[阅读次数:25 ]
  • Reality over Web:Pervasive Computing Meets the Web

    Muthucumaru Maheswaran;Devarun Bhattacharya;

    Reality over Web(RoW)is a novel concept,where a window on the web corresponds to a window onto a real space.Once the correspondence is established,users should be able to interact or manipulate the objects or people in the real space through the web window.In this paper,we introduce the RoW concept and highlight the principles that govern its design and implementation.A system architecture for realizing the RoW concept is described along with a proof-of-concept prototype that implements portions of the RoW concept.One essential part of an RoW implementation is accurate locationing of objects and people in a video frame.The locationing problem becomes particularly challenging because we want to reuse existing infrastructure as much as possible.We developed a high-frequency sound-based locationing scheme and implemented it on the prototype.The results from initial experiments performed on the locationing scheme are reported here.

    2013年06期 v.18 568-576页 [查看摘要][在线阅读][下载 1165K]
    [下载次数:36 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:31 ]
  • Comparison of Parallelization Strategies for Min-Sum Decoding of Irregular LDPC Codes

    Hua Xu;Wei Wan;Wei Wang;Jun Wang;Jiadong Yang;Yun Wen;

    Low-Density Parity-Check(LDPC)codes are powerful error correcting codes.LDPC decoders have been implemented as efficient error correction codes on dedicated VLSI hardware architectures in recent years.This paper describes two strategies to parallelize min-sum decoding of irregular LDPC codes.The first implements min-sum LDPC decoders on multicore platforms using OpenMP,while the other uses the Compute Unified Device Architecture(CUDA)to parallelize LDPC decoding on Graphics Processing Units(GPUs).Empirical studies on data with various scales show that the performance of these decoding processes is improved by these parallel strategies and the GPUs provide more efficient,fast implementation decoder.

    2013年06期 v.18 577-587页 [查看摘要][在线阅读][下载 1771K]
    [下载次数:51 ] |[网刊下载次数:0 ] |[引用频次:6 ] |[阅读次数:36 ]
  • CUDA's Mapped Memory to Support I/O Functions on GPU

    Wei Wu;Fengbin Qi;Wangquan He;Shanshan Wang;

    The API interfaces provided by CUDA help programmers to get high performance CUDA applications in GPU,but they cannot support most I/O operations in device codes.The characteristics of CUDA’s mapped memory are used here to create a dynamic polling service model in the host which can satisfy most I/O functions such as read/write file and"printf".The technique to implement these I/O functions has some influence on the performance of the original applications.These functions quickly respond to the users’I/O requirements with the"printf"performance better than CUDA’s.An easy and effective real-time method is given for users to debug their programs using the I/O functions.These functions improve productivity of converting legacy C/C++codes to CUDA and broaden CUDA’s functions.

    2013年06期 v.18 588-598页 [查看摘要][在线阅读][下载 20556K]
    [下载次数:39 ] |[网刊下载次数:0 ] |[引用频次:6 ] |[阅读次数:63 ]
  • Intermediate Spoofing Strategies and Countermeasures

    Yang Gao;Hong Li;Mingquan Lu;Zhenming Feng;

    Intermediate spoofing can impact most off-the-shelf Global Navigation Satellite Systems(GNSS)receivers,therefore low cost detection of such spoofing is very important to protect the reliability of the GNSS receivers used in critical safety and financial applications.This paper presents two strategies to analyze attacks by intermediate spoofing attackers to identify the weaknesses of such attacks.The analyses lead to a code and carrier phase consistency detection method with simulation results showing that this method can indicate the receiver when spoofing has occurred.The method can be used by most receivers,is inexpensive,and requires only a small software upgrade.

    2013年06期 v.18 599-605页 [查看摘要][在线阅读][下载 2018K]
    [下载次数:69 ] |[网刊下载次数:0 ] |[引用频次:18 ] |[阅读次数:62 ]
  • Automatic Collecting Representative Logo Images from the Internet

    Xiaobing Liu;Bo Zhang;

    With the explosive growth of commercial logos,high quality logo images are needed for training logo detection or recognition systems,especially for famous logos or new commercial brands.This paper focuses on automatic collecting representative logo images from the internet without any human labeling or seed images.We propose multiple dictionary invariant sparse coding to solve this problem.This work can automatically provide prototypes,representative images,or weak labeled training images for logo detection,logo recognition,trademark infringement detection,brand protection,and ad-targeting.The experiment results show that our method increases the mean average precision for 25 types of logos to 80.07%whereas the original search engine results only have32%representative logo images.The top images collected by our method are accurate and reliable enough for practical applications in the future.

    2013年06期 v.18 606-617页 [查看摘要][在线阅读][下载 2854K]
    [下载次数:42 ] |[网刊下载次数:0 ] |[引用频次:4 ] |[阅读次数:50 ]
  • Performance Prediction for Performance-Sensitive Queries Based on Algorithmic Complexity

    Chihung Chi;Ye Zhou;Xiaojun Ye;

    Performance predictions for database queries allow service providers to determine what resources are needed to ensure their performance.Cost-based or rule-based approaches have been proposed to optimize database query execution plans.However,Virtual Machine(VM)-based database services have little or no sharing of resources or interactions between applications hosted on shared infrastructures.Neither providers nor users have the right combination of visibility/access/expertise to perform proper tuning and provisioning.This paper presents a performance prediction model for query execution time estimates based on the query complexity for various data sizes.The user query execution time is a combination of five basic operator complexities:O.1/,O.log.n//,O.n/,O.n log.n//,and O.n2/.Moreover,tests indicate that not all queries are equally important for performance prediction.As such,this paper illustrates a performance-sensitive query locating process on three benchmarks:RUBiS,RUBBoS,and TPC-W.A key observation is that performance-sensitive queries are only a small proportion(20%)of the application query set.Evaluation of the performance model on the TPC-W benchmark shows that the query complexity in a real life scenario has an average prediction error rate of less than 10%which demonstrates the effectiveness of this predictive model.

    2013年06期 v.18 618-628页 [查看摘要][在线阅读][下载 531K]
    [下载次数:27 ] |[网刊下载次数:0 ] |[引用频次:0 ] |[阅读次数:31 ]
  • Efficient Leave-One-Out Strategy for Supervised Feature Selection

    Dingcheng Feng;Feng Chen;Wenli Xu;

    Feature selection is a key task in statistical pattern recognition.Most feature selection algorithms have been proposed based on specific objective functions which are usually intuitively reasonable but can sometimes be far from the more basic objectives of the feature selection.This paper describes how to select features such that the basic objectives,e.g.,classification or clustering accuracies,can be optimized in a more direct way.The analysis requires that the contribution of each feature to the evaluation metrics can be quantitatively described by some score function.Motivated by the conditional independence structure in probabilistic distributions,the analysis uses a leave-one-out feature selection algorithm which provides an approximate solution.The leave-oneout algorithm improves the conventional greedy backward elimination algorithm by preserving more interactions among features in the selection process,so that the various feature selection objectives can be optimized in a unified way.Experiments on six real-world datasets with different feature evaluation metrics have shown that this algorithm outperforms popular feature selection algorithms in most situations.

    2013年06期 v.18 629-635页 [查看摘要][在线阅读][下载 695K]
    [下载次数:62 ] |[网刊下载次数:0 ] |[引用频次:5 ] |[阅读次数:25 ]
  • Exploitation of Locality for Energy Efficiency for Breadth First Search in Fine-Grain Execution Models

    Chen Chen;Souad Koliai;Guang Gao;

    In the upcoming exa-scale era,the exploitation of data locality in parallel programs is very important because it benefits both program performance and energy efficiency.However,this is a hard topic for graph algorithms such as the Breadth First Search(BFS)due to the irregular data access patterns.This study analyzes the exploitation of data locality in the BFS and its impact on the energy efficiency with the Codelet fine-grain dataflow-inspired execution model.The Codelet Model more efficiently exploits data locality than the OpenMP-like execution models which traditionally focus on coarse-grain parallelism inside loops.A BFS algorithm is then given to exploit the locality between two loop iterations that belong to two different loops(inter-loop locality).This kind of locality can be exploited by the Codelet Model but not by traditional coarse-grain execution models like OpenMP.Tests were performed on fsim which is a simulation platform developed by Intel for the Ubiquitous High Performance Computing(UHPC)project to design future exa-scale architectures.The results show that this BFS algorithm saves up to 7%of the dynamic energy for memory accesses compared to a BFS implementation based on OpenMP loop scheduling.

    2013年06期 v.18 636-646页 [查看摘要][在线阅读][下载 1408K]
    [下载次数:37 ] |[网刊下载次数:0 ] |[引用频次:1 ] |[阅读次数:28 ]
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