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The breaking point between fast-and slow-light in a degenerate two-level atomic system

Chinese Physics B 2010年第6期19卷 325-329页

作者：李路明胡振燕罗斌郭弘 Department of Communication Jiangxi Electric Power Information and Communication Company CREAM Group State Key Laboratory of Advanced Optical Communication Systems and Networks (Peking University) and Institute of Quantum ElectronicsSchool of Electronics Engineering and Computer SciencePeking University

This paper investigates the breaking point between fast- and slow-light in a degenerate two-level atomic system, where fast-light can be converted to slow-light arbitrarily on a single transition line by adjusting the strength of the pumping field. An equivalent incoherent pumping rate is introduced in this simplified theoretical model which exploits the dependence of this feature. The experimental observation is presented as evidence of the breaking point where the injected power is about 0.08 mW.

关键词： degenerate two-level atomic system breaking point group velocity

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Three-Step Carrier Frequency Offset Estimation Algorithm for Burst-Mode communications

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电子学报(英文版) 2010年第1期19卷 165-169页

作者： LUO Wu LIU An LIANG Qinglin State Key Laboratory of Advanced Optical Communication Systems and Networks School of Electronic Engineering and Computer Science Peking University Beijing 100871 China

A data-aided frequency offset estimation algorithm suited for burst-mode communications is described and analyzed. The proposed algorithm is based on a Pilot symbol assisted modulation (PSAM) frame structure, which consists of regularly spaced pilot symbols and a group of consecutive pilot symbols embedded in. Firstly, an initial estimate based on consecutive pilot symbols is generated for reducing the phase ambiguity. Secondly, based on both spaced and consecutive pilot symbols, fine preliminary estimates are generated to improve estimation accuracy. Lastly, the final estimate is obtained by combining the fine preliminary estimates with the initial. This three-step algorithm is shown to provide high estimation accuracy close to those of FFT-based algorithm at low Signal-to-noise ratio (SNR). In addition, it is suitable for high carrier frequency offset cases.

关键词：频偏估计算法突发模式载波频偏通讯导频符号辅助载波频率偏移 FFT算法 PSAM

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The wireless sensor network localization algorithm based on improved pattern genetic algorithm

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Journal of Computational Information Systems 2011年第9期7卷 3031-3038页

作者： Huang, Haiping Cai, Qiwang Wang, Ruchuan She, Baoyang Ma, Yujing College of Computer Nanjing University of Posts and Telecommunications Nanjing 210003 China Jiangsu High Technology Research Key Laboratory for Wireless Sensor Networks Nanjing University of Posts and Telecommunications Nanjing 210003 China Key Lab. of Broadband Wireless Communication and Sensor Network Technology of Ministry of Education Nanjing University of Posts and Telecommunications Nanjing 210003 China College of Computer Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

Localization is one of the important technical issues of wireless sensor networks. Based on the traditional genetic algorithm applied in node localization, this paper introduces pattern search algorithm for the selection of population, meanwhile, genetic operators are designed. The theoretical analysis and simulation results show that, even though the proportion of anchor nodes and network connectivity is poor, and distance measurements are corrupted by Gaussian noise, the improved algorithm achieves high accuracy. Thus, it can be applied to most large-scale wireless sensor networks for node localization. © 2005 by Binary Information Press.

关键词： Genetic algorithms

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Advanced interference mitigation with frequency reuse schemes in the IEEE 802.16m uplink

Advanced interference mitigation with frequency reuse scheme...

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13th ACM International Conference on Modeling, Analysis and Simulation of Wireless and Mobile Systems, MSWiM 2010

作者： Wamser, Florian Mittelstädt, David Staehle, Dirk Tran-Gia, Phuoc University of Würzburg Institute of Computer Science Department of Communication Networks Würzburg Germany

ISBN: (纸本)9781450302746

Fractional frequency reuse is one of the key interference mitigation schemes of the IEEE 802.16m draft standard. This paper proposes a resource allocation strategy for the uplink fractional frequency reuse in the variant soft frequency reuse. Soft frequency reuse means that the resources of every sector are separated into a home partition and two side partitions. While resources of the home partition may be allocated to all users, resources of the side partitions are available for cell center users only. The main contribution of this paper is to use the most robust and power-efficient modulation and coding schemes on the side partitions as long as resources are available. A simulation study shows that with non-saturated users the system capacity can be increased when preferring power-efficient modulation and coding schemes on the side partitions. © 2010 ACM.

关键词： Orthogonal frequency division multiplexing

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Strong and affordable location privacy in VANETs: Identity diffusion using time-slots and swapping

Strong and affordable location privacy in VANETs: Identity d...

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2010 IEEE Vehicular Networking Conference, VNC 2010

作者： Eckhoff, David Sommer, Christoph Gansen, Tobias German, Reinhard Dressler, Falko Computer Networks and Communication Systems Dept. of Computer Science University of Erlangen Germany Audi Electronics Venture GmbH Gaimersheim Germany

ISBN: (纸本)9781424495252

Public acceptance, and thus the economical success of Vehicular Ad Hoc networks (VANETs), is highly dependent on the quality of deployed privacy mechanisms. Neither users nor operators should be able to track a given individual. One approach to facilitate this is the usage of pseudonym pools, which allow vehicles to autonomously switch between different identities. We extend this scheme with that of a time-slotted pseudonym pool of static size, reducing the storage and computation needs of the envisioned Intelligent Transportation System (ITS) while further improving users' privacy. In addition, we allow the exchange of pseudonyms between nodes, eliminating the mapping between vehicles and pseudonyms even for operators of the VANET. Here, we support the exchange of both the currently used pseudonym and those of future time-slots, further enhancing users' privacy. We evaluate the feasibility of our approach and back up privacy claims by performing a simulative study of the system using the entropy of nodes' anonymity sets as the primary metric. © 2010 IEEE.

关键词： Vehicular ad hoc networks

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An implementation and optimization for scalable DHT crawler

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science China(Information sciences) 2010年第4期53卷 769-779页

作者： ZHOU Mo1*, ZHANG JianYu2 & DAI YaFei1 1The National Laboratory on Local Fiber-Optic communication networks and Advanced Optical communication Systems of Peking University, Beijing 100871, China 2Institute of computer science and Technology of Peking University, Beijing 100871, China 1. The National Laboratory on Local Fiber-Optic Communication Networks and Advanced Optical Communication Systems of Peking University Beijing 100871 China2. Institute of Computer Science and Technology of Peking University Beijing 100871 China

KAD is one of the largest scale DHT based on real applications. Measurements on KAD is a good approach for researching DHT. Many different active and passive measurements have been made on those systems, and crawlers are novel approach in active measurement. A crawler begins crawling into the DHT with a basic set of given nodes, sending node searching requests to the nodes in the given set for contact information from more unknown nodes. There are three goals in mind while we design the crawler: finishing crawling the given nodes set as soon as possible; retrieving more nodes information after the crawling; getting result while sending as few network packets as possible. The above goals are correlated with each other. Optimizing one may impact others. This paper proposes a basic DHT crawler framework and discusses possible extension to the framework. After that we exploit the fact that the connectivity in the overlay network is universality, thus we do not need to crawl the whole overlay network space while maintaining the crawling affect.

关键词： DHT crawler network measurements

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Greedy design of resilient multi-layer networks

Greedy design of resilient multi-layer networks

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6th Euro NF Conference on Next Generation Internet, NGI 2010

作者： Duelli, Michael Qin, Xiaohua Menth, Michael University of Würzburg Institute of Computer Science Department of Communication Networks Am Hubland 97074 Würzburg Germany

ISBN: (纸本)9781424481668

In this paper, we propose a deterministic greedy heuristic providing a construction layout for a cost-efficient multilayer network that is able to carry a given set of traffic demands with and without protection on different layers. We apply the heuristic to different reference network topologies and protection requirements. Evaluations are conducted regarding equipment cost on different layers, blocking probability, path lengths, and number of demands affected by specific failures.

关键词： Blocking probability

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Scheduling complex automotive embedded real-time systems

Scheduling complex automotive embedded real-time systems

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2010 IEEE International Conference on Vehicular Electronics and Safety, ICVES 2010

作者： Lauer, Christoph Hielscher, Kai-Steffen German, Reinhard Pollmer, Jens Department of Computer Science 7 Computer Networks and Communication Systems University of Erlangen-Nuremberg Germany Department of Safety Electronics Audi AG Ingolstadt Germany

ISBN: (纸本)9781424471249

The formal verification of task schedulability is getting more important in the automotive domain as more and more applications are integrated into domain specific controllers. Especially for safety critical applications an indepth knowledge about the worst-case response time of tasks is of utmost importance. Such systems often consist of subsystems that comprise of a collection of tasks, called transactions, which are triggered by external events. We adapt a well known response time analysis to analyze asynchronous task sets where subsets may be triggered from different clock references. Therefore we refine the original computational model from the literature to capture the information about transaction clock references. To determine the schedulability of the system we first analyze all task subsets which are triggered by the same clock reference. Then we combine the results to derive the response times for the complete task set. The approach incorporates no overestimation of the response times and therefore represets a necessary and sufficient schedulability test for such systems. The computational complexity of the presented approach is O(n m) with n being the number of tasks and m the number of clock references in the system. We apply the analysis to a real-world scenario from the automotive safety domain to confirm the computational © 2010 IEEE.

关键词： Clocks

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ColorCom2: A transparent co-located virtual machine communication mechanism

ColorCom2: A transparent co-located virtual machine communic...

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International Conference on Computational science and Engineering

作者： Zhang, Liang Bai, Yuebin Liu, Ming Xu, Hanwen School of Computer Science Beihang University Beijing 100191 China Science and Technology on Information Transmission Dissemination in Communication Networks Laboratory Shijiazhuang 050081 China

ISBN: (纸本)9780769543239

In a virtualized environment, all the resource are managed by a virtual machine monitor (VMM). Virtualization technology creates separate, isolated and secure running environments for operating systems, programs or applications respectively. As the rapid development of hardware, the computing resource becomes abundant, which is a great chance for virtualization to extend its utilization, besides the amount of virtual machines (VMs) built and supported on a solid computing platform also increases rapidly. When a large amount of communication intensive software, such as web service, database center and gateway or domain name server, are deploying on virtualized environment, they have a demand for communicate with each other. For a mature virtual machine monitor, LAN-styled network communication mechanism for co-located virtual machines is a component of necessity. Although this is easy to use and transparent to user space programs and applications, the performance is often not so good to meet this demand because of the isolation barrier brought by the VMM. In this paper, we propose ColorCom2, a transparent co-located virtual machine communication mechanism. It applies directly memory copying and bypasses the traditional split driver model, producing a high performance in co-located virtual machine communication, and it also keeps transparent to upper level programs so any modification of program is not necessary. Also, ColorCom2 has an advantage over some other similar work is that it can work well although in the case that the underlay network device is interrupted. We use benchmarks and common programs to testColorCom2 in Xen hyper visor and the evaluation result have demonstrated that it has an explicit performance boost and a lower resource cost than the in-built co-located virtual machine communication mechanism. Meanwhile, the philosophy behind the design and implementation of ColorCom2 is almost universally applicable in any type of virtual machine. © 2010 IEEE

关键词： Virtual machine

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SoftAccel: A software-only IP network application accelerator

SoftAccel: A software-only IP network application accelerato...

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2010 IEEE Asia-Pacific Services Computing Conference, APSCC 2010

作者： Zhang, Huiyong Bai, Yuebin Li, Zhi Peng, Huixing Liu, Xiaoxia Zhao, Likun Wu, Wei Luo, Lianhe School of Computer Science Beihang University Beijing 100191 China Science and Technology on Information Transmission Dissemination in Communication Networks Laboratory Shijiazhuang 050081 China

ISBN: (纸本)9780769543055

Internet technologies are making rapid progress, but achieving high performance of network application over the WAN remains a challenge. When branch office's workers access enterprise applications locating in data center, the performances drop dramatically. To solve this problem, many hardware accelerators are produced. In this paper, we introduce a Software-only IP Network Application Accelerator (SoftAccel), for improving network applications performance over the WAN. To overcome the performance-limiting factors associated with WAN, transport protocol and application protocol, SoftAccel combines application proxy, delta compress and TCP optimization techniques. We have implemented SoftAccel in the form of framework, so people can design and test their optimization technologies based on it. Experiments in WAN environment show that SoftAccel can improve the performance of IP network applications at least by 2x. © 2010 IEEE.

关键词： Application programs

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