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Search Results: 1 - 10 of 40119 matches for " Chi Zhou "
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A Cooperative Scheme for Spectrum Sensing in Cognitive Radio Systems
Adamant Sula,Chi Zhou
Journal of Communications , 2009, DOI: 10.4304/jcm.4.10.741-751
Abstract: As wireless communication systems become more and more pervasive, demand for spectrum is following an ever increasing trend. At the same time, studies conducted by governmental bodies show that a considerable part of the allocated spectrum is underutilized. This paper aims to design and develop a cooperative spectrum sensing scheme from a comprehensive perspective including sensing, communication, decision, and transmission along with some other additional features. The scheme is based on dynamic weighting of cooperating users according to their reliability based on historical decision data. The work is articulated into a model development, the definition of mathematical metrics, and rounds of simulations to asses the validity of the model. Simulation results indicate that the model provides an adequate answer to some of the most challenging aspects of cognitive spectrum sensing.
Syntheses, Structures and Properties of 3d-4f Heterometallic Coordination Polymers Based on Tetradentate Metalloligand and Lanthanoid Ions  [PDF]
Xingnan Guo, Jun Qian, Qiang Zhou, Chi Zhang
Journal of Materials Science and Chemical Engineering (MSCE) , 2018, DOI: 10.4236/msce.2018.64016
Abstract: Based on tetradentate metalloligand LCu ([Cu(2,4-pydca)2], 2,4-pydca = pyridine-2,4-dicarboxylate) and lanthanides (Sm3+, Dy3+), two 3d-4fheterometalliccoordination polymers, namely, {[Sm2 (DMSO)4 (CH3OH) 2][LCu]3·7DMSO·2CH3OH}n 1 and {[Dy2 (DMSO)3 (CH3OH)][LCu3 (DMSO)]·4DMSO·CH3OH}n 2 (DMSO = dimethyl sulfoxide), have been synthesized and well characterized by elemental analysis, Fourier-transform infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. Single-crystal X-ray analysis reveals that both 1 and 2 crystallize in the triclinic crystal system with P-1 space group and possess the 3D framework structures, which are constructed from metalloligands LCu connecting with {Sm2} and {Dy2} clusters, respectively. The 3D structure of 1 has a 6-connected single-nodal topology with the point symbol {49 × 66}, while 2 features a different framework with the point symbol of {412 × 63}. Thermogravimetric analysis exhibits that the skeleton of both 1 and 2 collapse after 350℃. Magnetic properties of 1 and 2 have also been investigated.
Fast Detection Method in Cooperative Cognitive Radio Networks
Zhengyi Li,Lin Liu,Chi Zhou
International Journal of Digital Multimedia Broadcasting , 2010, DOI: 10.1155/2010/160462
Abstract: Cognitive Radio (CR) technology improves the utilization of spectrum highly via opportunistic spectrum sharing, which requests fast detection as the spectrum utilization is dynamic. Taking into consideration the characteristic of wireless channels, we propose a fast detection scheme for a cooperative cognitive radio network, which consists of multiple CRs and a central control office. Specifically, each CR makes individual detection decision using the sequential probability ratio test combined with Neyman Pearson detection with respect to a specific observation window length. The proposed method upper bounds the detection delay. In addition, a weighted out of fusion rule is also proposed for the central control office to reach fast global decision based on the information collected from CRs, with more weights assigned for CRs with good channel conditions. Simulation results show that the proposed scheme can achieve fast detection while maintaining the detection accuracy. 1. Introduction In the traditional management of licensed spectrum, users usually pay and have the exclusive access of spectrum with a certain level of Quality of Service (QoS) guarantee. On one hand, the spectrum is getting more and more crowded as the number of wireless devices increases drastically. However, on the other hand, the utilization of spectrum at any given time is low. Figure 1 shows a measurement of 30M–3GHz spectrum utilization. We can see that a lot of spectrum bands are vacant. Therefore, it would be efficient to allow unlicensed users to share spectrum with licensed users by using a vacant frequency band. Figure 1: A measurement of 30M–3GHz spectrum utilization. Cognitive Radio technology is developed to utilize these white spaces intelligently [1, 2]. FCC Spectrum Policy Task Force published a new spectrum management policy, open access or license exempted model, in 2002, to allow unlicensed user to use the opportunistic spectrum. As the transition from analog to digital television is complete, there are vacant channels (white spaces) in every media market [3]. Accordingly, the FCC announced a Notice of Proposed Rule Making (NPRM) on 13 May 2004, which proposed “to allow unlicensed radio transmitters to operate in the broadcast TV spectrum at locations where that spectrum is not being used”. Seen as the secondary user, the cognitive radio (CR) must avoid interfering with primary user (PU), that is, licensed user, while sharing the licensed band with the PU. Therefore, cognitive radio needs to sense the spectrum to detect the existence of PU, identify the white spaces
Backpropagation-Based Cooperative Localization of Primary User for Avoiding Hidden-Node Problem in Cognitive Networks
Lin Liu,Zhengyi Li,Chi Zhou
International Journal of Digital Multimedia Broadcasting , 2010, DOI: 10.1155/2010/905321
Abstract: Cognitive radio (CR) is a technology to implement opportunistic spectrum sharing to improve the spectrum utilization. However, there exists a hidden-node problem, which can be a big challenge to solve especially when the primary receiver is passive listening. We aim to provide a solution to the hidden-node problem for passive-listening receiver based on cooperation of multiple CRs. Specifically, we consider a cooperative GPS-enabled cognitive network. Once the existence of PU is detected, a localization algorithm will be employed to first estimate the path loss model for the environment based on backpropagation method and then to locate the position of PU. Finally, a disable region is identified taking into account the communication range of both the PU and the CR. The CRs within the disabled region are prohibited to transmit in order to avoid interfering with the primary receiver. Both analysis and simulation results are provided. 1. Introduction As more devices go wireless, spectrum becomes more and more crowded. Study of spectrum utilization, however, reveals that not all the spectrum is in use for all the time. Enforcement Bureau of Federal Communications Commission (FCC) measures the spectrum usage in Atlanta, Chicago, and so forth, and the study shows that only 5%–10% of the spectrum is used (up to 100?GHz) on the average. DARPA study reveals that only 2% of the allocated spectrum is used at any given time. Therefore, there is a potential to make efficient use of the unused spectrum without interfering with primary users (PUs) so that the spectrum utilization can be improved and more users can be supported. Cognitive radio (CR) is a technology to implement opportunistic spectrum sharing to improve the spectrum utilization [1–3]. CR can be applied in civilian applications, law enforcement, as well as military applications. For CR, spectrum sensing is the first step but very crucial to the success. Only when the electromagnetic environment is thoroughly understood, it can be decided over which frequency to transmit and how to transmit. As the cognitive radio is seen as the secondary user to share the licensed band with the PU, they must avoid or control the interference to potential PU. However, as a radio device, a single CR may suffer severe shadowing or multipath fading with respect to primary transmitter so that it cannot detect the existence of primary transmitter even in its vicinities. In addition, there exists a hidden-node problem, in which a CR may be too far from the transmitter to detect the existence of the PU, but close to the primary
Building Automation Networks for Smart Grids
Peizhong Yi,Abiodun Iwayemi,Chi Zhou
International Journal of Digital Multimedia Broadcasting , 2011, DOI: 10.1155/2011/926363
Abstract: Smart grid, as an intelligent power generation, distribution, and control system, needs various communication systems to meet its requirements. The ability to communicate seamlessly across multiple networks and domains is an open issue which is yet to be adequately addressed in smart grid architectures. In this paper, we present a framework for end-to-end interoperability in home and building area networks within smart grids. 6LoWPAN and the compact application protocol are utilized to facilitate the use of IPv6 and Zigbee application profiles such as Zigbee smart energy for network and application layer interoperability, respectively. A differential service medium access control scheme enables end-to-end connectivity between 802.15.4 and IP networks while providing quality of service guarantees for Zigbee traffic over Wi-Fi. We also address several issues including interference mitigation, load scheduling, and security and propose solutions to them. 1. Introduction The smart grid is an intelligent power generation, distribution, and control system. It enhances today’s power grid with intelligence, bidirectional communication capabilities and energy flows [1]. These enhancements address the efficiency, stability, and flexibility issues that plague the grid at present. In order to achieve its promised potential, the smart grid must facilitate services including the wide-scale integration of renewable energy sources, provision of real-time pricing information to consumers, demand response programs involving residential and commercial customers, and rapid outage detection. All these tasks demand the collection and analysis of real-time data. This data is then used to control electrical loads and perform demand response. In order to obtain the full benefit of smart grids, their communication infrastructure must support device control and data exchanges between various domains which comprise the smart grid. The smart grid must be allied with smart consumption in order to achieve optimum power system efficiency. This necessitates the integration of smart buildings, appliances, and consumers in order to reduce energy consumption while satisfying occupant comfort. Building automation systems (BASs) already provide this intelligence, enabling computerized measurement, control and management of heating, ventilation, air-conditioning (HVAC), lighting, and security systems to enhance energy efficiency, reduce costs, and improve user comfort. Buildings consume 29% of all electricity generated in the United States [2]; therefore, the ability of BASs to communicate
K-Gram Based Fuzzy Keyword Search over Encrypted Cloud Computing  [PDF]
Wei Zhou, Lixi Liu, He Jing, Chi Zhang, Shaowen Yao, Shipu Wang
Journal of Software Engineering and Applications (JSEA) , 2013, DOI: 10.4236/jsea.2013.61004
Abstract:

With recent significant development in the portable device market, cloud computing is getting more and more utilized. Many sensitive data are stored in cloud central servers. To ensure privacy, these data are usually encrypted before being uploaded—making file searching complicated. Although previous cloud computing searchable encryption schemes allow users to search encrypted data by keywords securely, these techniques only support exact keyword search and will fail if there are some spelling errors or if some morphological variants of words are used. In this paper, we provide the solution for fuzzy keyword search over encrypted cloud data. K-grams is used to produce fuzzy results. For security reasons, we use two separate servers that cannot communicate with each other. Our experiment result shows that our system is effective and scalable to handle large number of encrypted files.

Chronic gastritis treated by acupuncture combined with Chinese herbs: A report of 110 cases
ZHANG Chi,ZHOU Zhang-Ling
Zhong Xi Yi Jie He Xue Bao , 2003,
Abstract:
Electron gun system for NSC KIPT linac
Zusheng Zhou,Dayong He,Yunlong Chi
Physics , 2013, DOI: 10.1088/1674-1137/38/6/067006
Abstract: In NSC KIPT linac, a neutron source based on a subcritical assembly driven by a 100MeV/100kW electron linear accelerator is under design and development. The linear accelerator needs a new high current electron gun. In this paper, the physical design, mechanical fabrication and beam test of this new electron gun are described. The emission current is designed to be higher than 2A for the pulse width of 3us with repetition rate of 50 Hz. The gun will operate with a DC high voltage power supply which can provide a high voltage up to 150 kV. . Computer simulations and optimizations have been carried out in the design stage, including the gun geometry and beam transport line. The test results of high voltage conditioning and beam test are presented. The operation status of the electron gun system is also included. The basic test results show that the design, manufacture and operation of the new electron system are basically successful.
Distance Majorization and Its Applications
Eric C. Chi,Hua Zhou,Kenneth Lange
Mathematics , 2012, DOI: 10.1007/s10107-013-0697-1
Abstract: The problem of minimizing a continuously differentiable convex function over an intersection of closed convex sets is ubiquitous in applied mathematics. It is particularly interesting when it is easy to project onto each separate set, but nontrivial to project onto their intersection. Algorithms based on Newton's method such as the interior point method are viable for small to medium-scale problems. However, modern applications in statistics, engineering, and machine learning are posing problems with potentially tens of thousands of parameters or more. We revisit this convex programming problem and propose an algorithm that scales well with dimensionality. Our proposal is an instance of a sequential unconstrained minimization technique and revolves around three ideas: the majorization-minimization (MM) principle, the classical penalty method for constrained optimization, and quasi-Newton acceleration of fixed-point algorithms. The performance of our distance majorization algorithms is illustrated in several applications.
Monetary Cost Optimizations for Hosting Workflow-as-a-Service in IaaS Clouds
Amelie Chi Zhou,Bingsheng He,Cheng Liu
Computer Science , 2013,
Abstract: Recently, we have witnessed workflows from science and other data-intensive applications emerging on Infrastructure-asa-Service (IaaS) clouds, and many workflow service providers offering workflow as a service (WaaS). The major concern of WaaS providers is to minimize the monetary cost of executing workflows in the IaaS cloud. While there have been previous studies on this concern, most of them assume static task execution time and static pricing scheme, and have the QoS notion of satisfying a deterministic deadline. However, cloud environment is dynamic, with performance dynamics caused by the interference from concurrent executions and price dynamics like spot prices offered by Amazon EC2. Therefore, we argue that WaaS providers should have the notion of offering probabilistic performance guarantees for individual workflows on IaaS clouds. We develop a probabilistic scheduling framework called Dyna to minimize the monetary cost while offering probabilistic deadline guarantees. The framework includes an A*-based instance configuration method for performance dynamics, and a hybrid instance configuration refinement for utilizing spot instances. Experimental results with three real-world scientific workflow applications on Amazon EC2 demonstrate (1) the accuracy of our framework on satisfying the probabilistic deadline guarantees required by the users; (2) the effectiveness of our framework on reducing monetary cost in comparison with the existing approaches.
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