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Fast local reconstruction by selective backprojection for low dose in dental computed tomography

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Chinese Physics C 2014年第10期38卷 117-125页

作者：闫镔邓林韩玉张峰汪先超李磊 National Digital Switching System Engineering and technological Research center

The high radiation dose in computed tomography （CT） scans increases the lifetime risk of cancer, which becomes a major clinical concern. The backprojection-filtration （BPF） algorithm could reduce the radiation dose by reconstructing the images from truncated data in a short scan. In a dental CT, it could reduce the radiation dose for the teeth by using the projection acquired in a short scan, and could avoid irradiation to the other part by using truncated projection. However, the limit of integration for backprojection varies per PI-line, resulting in low calculation efficiency and poor parallel performance. Recently, a tent BPF has been proposed to improve the calculation efficiency by rearranging the projection. However, the memory-consuming data rebinning process is included. Accordingly, the selective BPF （S-BPF） algorithm is proposed in this paper. In this algorithm, the derivative of the projection is backprojected to the points whose x coordinate is less than that of the source focal spot to obtain the differentiated backprojection. The finite Hilbert inverse is then applied to each PI-line segment. S-BPF avoids the influence of the variable limit of integration by selective backprojection without additional time cost or memory cost. The simulation experiment and the real experiment demonstrated the higher reconstruction efficiency of S-BPF.

关键词： local reconstruction dental CT selective backprojection short scan

Dynamic hybrid multimedia distribution scheme based on network reconfiguration

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Science China(Information Sciences) 2014年第10期57卷 107-116页

作者： DONG Fang HU YuXiang LAN JuLong National Digital Switching System Engineering and technological Research center

This paper addresses a key challenge in the design and implementation of multimedia distribution systems so that users can experience good performance with minimal operational costs. In current structures,the conflict between network architectures and service provision causes a decline in users’ expectations of quality. Network reconfiguration provides a feasible solution for dynamic distribution as a primitive for both quality and efficiency. In this paper, we first present a scheme for a layer-based hybrid multimedia distribution system LHMDS, and then introduce a dynamic sliding push-delivery mechanism based on reconfiguration of the distribution of hotspot files. The LHMDS adopts a unique structure with hybrid channels, including broadcast and unicast ones, and adjusts its distribution topology according to the congestion status, thereby pushing hotspot files dynamically. The mechanism dynamically pushes files to upper or lower network layers depending on the network status while distributing hotspot files by broadcast channels and other files by unicast *** guarantees service quality as well as improving resource utilization. Finally, we validate the feasibility and performance of the scheme through a simulation.

关键词： network reconfiguration hybrid distribution dynamic sliding push-delivery

Fast parallel algorithm for three-dimensional distance-driven model in iterative computed tomography reconstruction

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Chinese Physics B 2015年第2期24卷 513-520页

作者：陈建林李磊王林元蔡爱龙席晓琦张瀚铭李建新闫镔 National Digital Switching System Engineering & technological R&D center

The projection matrix model is used to describe the physical relationship between reconstructed object and *** a model has a strong influence on projection and backprojection,two vital operations in iterative computed tomographic *** distance-driven model（DDM） is a state-of-the-art technology that simulates forward and back *** model has a low computational complexity and a relatively high spatial resolution;however,it includes only a few methods in a parallel operation with a matched model *** study introduces a fast and parallelizable algorithm to improve the traditional DDM for computing the parallel projection and backprojection *** proposed model has been implemented on a GPU（graphic processing unit） platform and has achieved satisfactory computational efficiency with no *** runtime for the projection and backprojection operations with our model is approximately 4.5 s and 10.5 s per loop,respectively,with an image size of 256×256×256 and 360 projections with a size of 512×*** compare several general algorithms that have been proposed for maximizing GPU efficiency by using the unmatched projection/backprojection models in a parallel *** imaging resolution is not sacrificed and remains accurate during computed tomographic reconstruction.

关键词： computed tomography iterative reconstruction parallelizable algorithm distance-driven model

Thoughts on the development of novel network technology

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Science China(Information Sciences) 2018年第10期61卷 144-154页

作者： Jiangxing WU National Digital Switching System Engineering and technological R&D center

In this paper, we explore potential innovations that could lead to breakthrough developments in Internet technologies. The deep integration of the Internet and economic society brings professionalized service capacity demand, while existing Internet infrastructure with its current technological systems still face a number of challenges, such as intelligence, diversification, personalization, robustness, and ***, we analyze the actual foundation of innovation and specify the basic technical features of a novel network. Then, we propose a fully dimensionally definable open architecture as the primary direction, and consider reshaping baseline technologies as a starting point and discuss the core operational mechanisms of the novel network based on such reshaped baseline technologies.

关键词： novel Internet technology open architecture full-dimensional definability diversified addressing and routing intelligence general robust control

An Approach for Network Function Combination Based on Least Busy Placement Algorithm

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China Communications 2016年第S1期13卷 167-176页

作者： XIE Lijun JIANG Yiming WANG Binqiang XIONG Gang CHENG Guozhen National Digital Switching System Engineering & technological Research center

Recently, integrating Softwaredefined networking(SDN) and network functions virtualization(NFV) are proposed to address the issue that difficulty and cost of hardwarebased and proprietary middleboxes management. However, it lacks of a framework that orchestrates network functions to service chain in the network cooperatively. In this paper, we propose a function combination framework that can dynamically adapt the network based on the integration NFV and SDN. There are two main contributions in this paper. First, the function combination framework based on the integration of SDN and NFV is proposed to address the function combination issue, including the architecture of Service Deliver Network, the port types representing traffic directions and the explanation of terms. Second, we formulate the issue of load balance of function combination as the model minimizing the standard deviations of all servers' loads and satisfying the demand of performance and limit of resource. The least busy placement algorithm is introduced to approach optimal solution of the problem. Finally, experimental results demonstrate that the proposed method can combine functions in an efficient and scalable way and ensure the load balance of the network.

关键词： software-defined networking network functions virtualization load balance least busy placement algorithm contribution degree

A Tractable Approach to Analyzing the Physical-Layer Security in K-Tier Heterogeneous Cellular Networks

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China Communications 2015年第S1期12卷 166-173页

作者： ZHONG Zhihao PENG Janhua LUO Wenyu HUANG Kaizhi National Digital Switching System Engineering & technological Research center

This study proposes a tractable approach to analyze the physical-layer security in the downlink of a multi-tier heterogeneous cellular network. This method is based on stochastic geometry, has low computational complexity, and uses the two-dimensional Poisson point process to model the locations of K-tier base stations and receivers, including those of legitimate users and eavesdroppers. Then, the achievable secrecy rates for an arbitrary user are determined and the upper and lower bounds of secrecy coverage probability derived on the condition that cross-tier interference is the main contributor to aggregate interference. Finally, our analysis results reveal the innate connections between information-theoretic security and the spatial densities of legitimate and malicious nodes.

关键词： heterogeneous cellular networks physical layer security stochastic geometry secrecy coverage probability

NBgossip:An Energy-Efficient Gossip Algorithm for Wireless Sensor Networks

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Journal of Computer Science & Technology 2008年第3期23卷 426-437页

作者：陆峰谢良镇郑国良钟伟豪 center for Multimedia and Network Technology School of Computer EngineeringNanyang Technological University

Gossip-based algorithms for information dissemination have recently received significant attention for sensor and ad hoc network applications because of their simplicity and robustness. However, a common drawback of many gossip-based protocols is the waste of energy in passing redundant information over the network. Thus gossip algorithms need to be re-engineered in order to become applicable to energy constrained networks. In this paper, we consider a scenario where each node in the network holds a piece of information （message） at the beginning, and the objective is to simultaneously disseminate all information （messages） among all nodes quickly and cheaply. To provide a practical solution to this problem for ad hoc and sensor networks, NBgossip algorithm is proposed, which is based on network coding and neighborhood gossip. In NBgossip, nodes do not simply forward messages they receive, instead, the linear combinations of the messages are sent out. In addition, every node exchanges messages with its neighboring nodes only. Mathematical proof and simulation studies show that the proposed NBgossip terminates in the optimal O（n）-order rounds and outperforms the existing gossip-based approaches in terms of energy consumption incurred in spreading all the information.

关键词： data dissemination gossip network coding sensor networks

Review on Security Defense Technology Research in Edge Computing Environment

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Chinese Journal of Electronics 2024年第1期33卷 1-18页

作者： Ke SHANG Weizhen HE Shuai ZHANG National Digital Switching System Engineering and technological R&D center

Edge computing, which achieves quick data processing by sinking data computing and storage to the network edge, has grown rapidly along with the Internet of things. The new network architecture of edge computing brings new security challenges. Based on this, this paper investigates the edge computing security literature published in recent years and summarizes and analyzes research work on edge computing security from different attack surfaces. We start with the definition and architecture of edge computing. From the attack surface between device and edge server, as well as on edge servers, the research describes the security threats and defense methods of edge computing. In addition, the cause of the attack and the pros and cons of defense methods is introduced. The challenges and future research directions of edge computing are given.

关键词： Cloud computing Systems architecture Computer architecture Network architecture Data processing Security Servers

Design and implementation of a novel enterprise network defense system by maneuvering multi-dimensional network properties

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Frontiers of Information Technology & Electronic Engineering 2019年第2期20卷 238-252页

作者： Yang CHEN Hong-chao HU Guo-zhen CHENG National Digital Switching System Engineering & technological R&D center

Although the perimeter security model works well enough when all internal hosts are credible, it is becoming increasingly difficult to enforce as companies adopt mobile and cloud technologies, i.e., the rise of bring your own device(BYOD). It is observed that advanced targeted cyber-attacks usually follow a cyber kill chain;for instance, advanced targeted attacks often rely on network scanning techniques to gather information about potential targets. In response to this attack method, we propose a novel approach, i.e., an "isolating and dynamic"cyber defense, which cuts these potential chains to reduce the cumulative availability of the gathered ***, we build a zero-trust network environment through network isolation, and then multiple network properties are maneuvered so that the host characteristics and locations needed to identify vulnerabilities cannot be ***, we propose a software-defined proactive cyber defense solution(SPD) for enterprise networks and design a general framework to strategically maneuver the IP address, network port, domain name, and path, while limiting the performance impact on the benign network user. Third, we implement our SPD proof-of-concept system over a software-defined network controller(OpenDaylight). Finally, we build an experimental platform to verify the system's ability to prevent scanning, eavesdropping, and denial-of-service attacks. The results suggest that our system can significantly reduce the availability of network reconnaissance scan information, block network eavesdropping, and sharply increase the cost of cyber-attacks.

关键词： Intranet defense Software-defined network Multi-dimensional maneuvering