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76 results on '"Liu Xiaochen"'

19. Trapezoidal Angled Fiber Coupler for Microsphere Resonator With Enhancement of Fano Resonance.

Author

Liu, Xiaochen, Zhang, Xiaobei, Zhang, Qi, Yang, Yong, Xie, Yan, Wang, Zijie, Sun, Hang, Huang, Yi, and Wang, Tingyun

Abstract

We propose and demonstrate a trapezoidal angled fiber coupler for excitation of whispering-gallery mode microsphere resonator, with enhanced Fano resonance. The reflection from the angled fiber is enhanced when the oblique angle is greater than critical angle, which is obtained as 30° theoretically for angled fiber. To enhance the endface reflection, the front tip of the angled fiber is polished flat to achieve the trapezoidal angled fiber. Compared with angled fiber, the proportion of Fano lineshape in spectra for trapezoidal angled fiber is nearly doubled and the slope is greatly improved, which reaches 304.55 dB/nm. Moreover, through the coupling of dual microspheres, the ${Q}$ factor is improved severalfold and the thermal tuning efficiency is increased by 50%. With the advantage of low cost, easy fabrication procedure and reflection mode operation, the proposed device shows a great potential for sensing, optical tuning and optical switching applications. [ABSTRACT FROM AUTHOR]

Published
2022
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20. Secrecy Throughput Optimization for the WPCNs With Non-Linear EH Model

Author

Mingxi Guo, Liu Xiaochen, Nan Sha, and Yuanyuan Gao

Subjects
General Computer Science, business.industry, Computer science, Transmitter, General Engineering, secrecy throughput, Throughput, Data_CODINGANDINFORMATIONTHEORY, physical layer security (PLS), Transmitter power output, non-linear energy harvesting (EH) model, Base station, Wireless powered communication networks (WPCNs), Secure communication, robust beamforming, Artificial noise, Wireless, General Materials Science, lcsh:Electrical engineering. Electronics. Nuclear engineering, business, lcsh:TK1-9971, Communication channel, Computer network, Computer Science::Cryptography and Security, Computer Science::Information Theory
Abstract

This paper investigates secure communication from a wireless-powered transmitter to a desired receiver with multiple eavesdroppers in the wireless powered communication networks (WPCNs). Considering the non-linear energy harvesting (EH) model, we propose a secure two-phase communication protocol with the help of a hybrid base station (HBS). First, in the power transfer (PT) phase, the HBS transfers wireless power to the transmitter. Then in the subsequent secure information transmission (SIT) phase, the transmitter sends the secret information using the energy harvested in the PT, under the protection of artificial noise (AN) generated by the HBS. First, based on this communication protocol, we maximize the secrecy throughput with perfect channel information state (CSI) under the transmit power constraint at the HBS. The secrecy throughput maximization (STM) problem is non-convex, and hence we reformulate it by exploiting the primal decomposition method (PDM) to obtain tractable forms. The PDM-based transmit scheme (PDM-TS) is proposed for the STM. In addition, considering the imperfect CSI of wiretap channel, we further design the robust transmit scheme for the worst-case secrecy throughput maximization (wSTM) problem. Since the wSTM shows high non-convexity, we extend the PDM by combining it with the S -procedure, and the PDM-based robust transmit scheme (PDM-RTS) is proposed for the wSTM. Finally, the numerical simulations are provided to show the effectiveness of the proposed transmit schemes.

Published
2019

24. Evaluation of Lucas-Kanade based optical flow algorithm

Author

Tang Jun, Liu Xiaochen, Liu Jun, Yang Jiangtao, Wang Linwei, Shen Chong, Wang Yubo, Xiong Yufeng, and Liu Xiaojie

Subjects
Lucas–Kanade method, Computer science, ComputingMethodologies_IMAGEPROCESSINGANDCOMPUTERVISION, Optical flow, ComputerApplications_COMPUTERSINOTHERSYSTEMS, Pyramid (image processing), Algorithm, Urban environment
Abstract

Since the performance of pyramid Lucas-Kanade (LK) based optical flow algorithm would be influenced by different environments, this paper evaluates the simulation accuracy of the pyramid LK algorithm in cities, plains and mountains, respectively. The simulation results show that the LK algorithm can maintain high precision under the large motion, and the flight strategy of UAV under different environment is given according to the algorithm’s accuracy, In order to ensure the high accuracy of the optical flow sensor in different environments. For example, in the urban environment, when the UAV’s velocity is 12m/s-l5m/s, the best altitude is 80m-l50m. Simulation verification experiments are carried out in different environments. The simulation results show that the proposed UAV flight strategy is generally correct.

Published
2018
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31. A new bionic structure of inspection robot for high voltage transmission line

Author

Lu Kunpeng, Liu Xiaochen, Liu Yi, Jidai Wang, and Jing Zhen

Subjects
Engineering, Robot kinematics, Bionics, Robot calibration, business.industry, 020209 energy, Control engineering, Mobile robot, 02 engineering and technology, Robot end effector, Robot control, law.invention, Computer Science::Robotics, law, Line (geometry), 0202 electrical engineering, electronic engineering, information engineering, Robot, business, Simulation
Abstract

Traditional inspection robot for high voltage transmission line robot is hard to cross the drainage line and other non straight line segment obstacle because of the small operation space. A new bionic structure of the inspection robot is proposed in this paper, which is combined the motion characteristics of primates with the modern design method and the principle of bionics. The mechanism model based on the three arms with symmetrical distributed and its crossing various obstacles on power line simulating to primates suspension pendulum movement are presented. The robot operation of crossing obstacle process is simulated and analyze with ADAMS software, thus the rationality and stability of the bionic mechanism are verified. Finally, the principle model and virtual prototype of robot are manufactured and testing on the practical power line.

Published
2016
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33. Distributionally Robust Optimization for Secure Transmission With Assisting Jammer in MISO Downlink Networks.

Author

Liu, Xiaochen, Gao, Yuanyuan, Wang, Lei, Sha, Nan, and Wang, Shijie

Abstract

This letter investigates secure transmission with imperfect channel state information (CSI) in multi-input single-output downlink wireless networks that consist of a transmitter, a desired receiver, one eavesdropper, and an assisting jammer. Specifically, only rough first- and second-order moment information is obtained for the estimation errors of CSI. We aim to minimize the total transmit power by jointly designing the beamforming vector at transmitter and artificial noise covariance at jammer under the reliability and secrecy constraints for all the possible distributions of CSI errors. Since the chance-constrained optimization problem is non-convex, we reformulate it using a Lagrangian duality theory and semidefinite relaxation. The simulation results illustrate the validity of the proposed distributionally robust transmit scheme. [ABSTRACT FROM AUTHOR]

Published
2019
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37. Data Acquisition for Real-Time Decision-Making under Freshness Constraints

Author

Hu, Shaohan, primary, Yao, Shuochao, additional, Jin, Haiming, additional, Zhao, Yiran, additional, Hu, Yitao, additional, Liu, Xiaochen, additional, Naghibolhosseini, Nooreddin, additional, Li, Shen, additional, Kapoor, Akash, additional, Dron, William, additional, Su, Lu, additional, Bar-Noy, Amotz, additional, Szekely, Pedro, additional, Govindan, Ramesh, additional, Hobbs, Reginald, additional, and Abdelzaher, Tarek F., additional

Published
2015
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41. The Spatial–Temporal Perspective: The Study of the Propagation of Modern Social Worms.

Author

Wang, Tianbo, Xia, Chunhe, Li, Zhong, Liu, Xiaochen, and Xiang, Yang

Abstract

Due to the critical security threats imposed by social worms, such as Twitter and Facebook, modeling and simulation study of the propagation dynamics of social worms is essential to predict their potential for damage and to understand the propagation characteristics. Modern social worms exhibit one new feature, reinfection-notification. It indicates that malicious messages are sent by neighbors whenever any susceptible or infected recipients open the malicious attachments, and a user will get reminders when new messages come to a social account. Meanwhile, there are two critical problems: dynamic host usage and temporal message processing. First, from a spatial perspective, previous models have not taken into account that public hosts in different locations are shared by several users arising from human mobility, namely, dynamic host usage. Second, from a temporal perspective, the problem of temporal message processing results from the improper assumption that during this period of message checking, unread messages all are read by default, or under the condition that some parts of messages have been read, but the rest of unread messages are no longer processed afterward. To address these problems, we present a novel social worm simulation model in this paper, which adopts “social network-based sharing” and “sorting and attenuation” methods. We perform comprehensive theoretical analyses and experimental evaluation to validate our simulation model. The results show that our model is more suitable for modeling the complicated propagation behaviors of modern social worms in hierarchical networks. [ABSTRACT FROM PUBLISHER]

Published
2017
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42. Machine Learning for Noise Sensor Placement and Full-Chip Voltage Emergency Detection.

Author

Liu, Xiaochen, Sun, Shupeng, Li, Xin, Qian, Haifeng, and Zhou, Pingqiang

Subjects
*MACHINE learning, *DETECTORS, *NOISE, *POWER resources, *ELECTRIC potential
Abstract

Power supply fluctuation can be potential threat to the correct operations of processors, in the form of voltage emergency that happens when supply voltage drops below a certain threshold. Noise sensors (with either analog or digital outputs) can be placed in the nonfunction area of processors to detect voltage emergencies by monitoring the runtime voltage fluctuations. Our work addresses two important problems related to building a sensor-based voltage emergency detection system: 1) offline sensor placement, i.e., where to place the noise sensors so that the number and locations of sensors are optimized in order to strike a balance between design cost and chip reliability and 2) online voltage emergency detection, i.e., how to use these placed sensors to detect voltage emergencies in the hotspot locations. In this paper, we propose integrated solutions to these two problems, respectively, for analog and digital (more specifically, binary) sensor outputs, by exploiting the voltage correlation between the sensor candidate locations and the hotspot locations. For the analog case, we use the Group Lasso and an ordinary least squares approach; for the binary case, we integrate the Group Lasso and the SVM approach. Experimental results show that, our approach can achieve 2.3X–2.7X better voltage emergency detection results on average for analog outputs when compared to the state-of-the-art work; and for the binary case, on average our methodology can achieve up to 21% improvement in prediction accuracy compared to an approach called max-probability-no-prediction. [ABSTRACT FROM AUTHOR]

Published
2017
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