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Four-level superradiant laser with full atomic cooperativity

Physical Review A 2010年第5期81卷 053809-053809页

作者： Deshui Yu Jingbiao Chen Department of Applied Physics Graduate School of Engineering The University of Tokyo Bunkyo-ku Tokyo 113-8656 Japan Institute of Quantum Electronics and State Key Laboratory of Advanced Optical Communication System & Network School of Electronics Engineering & Computer Science Peking University Beijing 100871 People's Republic of China State Key Laboratory of Precision Spectroscopy East China Normal University Shanghai 200062 People's Republic of China

We investigate a four-level superradiant laser whose intensity is proportional to N2 and whose linewidth scales as 1/N2. In the absence of spontaneous emissions, we derive the stationary solutions of the atomic full cooperativity, analyze their stabilities, and find the corresponding irreducible representation based on group U(4). We also investigate the spectra of the phase and amplitude fluctuations of the fields inside and outside the cavity and find that the amplitude fluctuations of the output fields cannot be squeezed in the low-frequency limit, which is completely different from the three-level superradiant laser system. Finally, we consider the stationary solutions corresponding to the partial cooperativity due to the symmetry breaking of U(4) induced by the atomic spontaneous emissions.

关键词： Spontaneous emission

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Impact of increasing threshold level on higher bit rate in free space optical communications

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Journal of Optical and Fiber communication Research 2009年第1-6期6卷 22-34页

作者： Hitam, Salasiah Abdullah, Mohd Khazani Mahdi, Mohd Adzir Harun, Harlisya Sali, Aduwati Fauzi, Mohd Department of Computer System and Communication Faculty of Engineering Universiti Putra Malaysia 43400 UPM Serdang Selangor Malaysia

The biggest challenge facing free space optical deployment is optical signal propagation in different atmospheric conditions such as fog, low clouds, rain, snow, dust, haze and various combinations of each. A transmission and detection technique for free space optical communications is proposed where it employs two beams, one modulated with the data, the other with the inverted version of the same data. A differential detection technique is used at the receiver whereby the inverted data are used as the reference to perform the decision making, as opposed to the fixed threshold used in the conventional technique. The probability of error under threshold instability in the proposed differential technique and Intensity Modulation/Direct Detection (IM/DD) technique are compared. A simulation under heavy rainfall condition of 8.33 × 10-4 cm/sec at bit rate of 155 Mbps to 10 Gbps with 0 dBm of launch power and 1.5 km distance shows that this technique achieves an improvement compared to the conventional IM/DD. The differential detection can support a higher bit rate (up to 9 Gbps) because of its noise reduction capabilities due to higher threshold level implemented in the receiver. The IM/DD in contrast, can support bit rates of only 2.5 Gbps. This analysis focuses on weather conditions in Malaysia. © Springer Science+Business Media, Inc. 2009.

关键词： Rain

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A High Efficiency and Multi-Band/Multi-Mode Power Amplifier using a Distributed Second Harmonic Termination

A High Efficiency and Multi-Band/Multi-Mode Power Amplifier ...

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European Microwave Conference (EuMC 2010)

作者： Jangheon Kim Farouk Mkadem Slim Boumaiza Telecommunication System Division Digital Media & Communication Business Samsung Electronics Co. Ltd Department of Electrical and Computer Engineering University of Waterloo

ISBN: (纸本)9781424472321

This paper proposes a new broadband saturated power amplifier (SPA) with a distributed second harmonic termination supporting multi-band/multi-mode operation. The proposed network is composed of a fundamental matching circuit and multiple second harmonic termination circuits. Due to the multiple harmonic terminations, the proposed PA improves the frequency range where the PA can achieve a high efficiency. The proposed PA is fabricated using a 45 W Cree CGH40045 GaN HEMT. Drain efficiencies of greater than 60% (average 66%) are achieved between about 1.8 GHz and 2.3 GHz (500 MHz bandwidth). When driven with long term evolution (LTE) and two carrier wideband code division multiple access (WCDMA) signals at DCS1800, PCS1900, and WCDMA bands, the linearity specifications of the corresponding standards are satisfied using the digital predistortion linearization technique, and it attains an efficiency of greater than 30%.

关键词： WCDMA second harmonics frequency ranges Nylons Power amplifiers stopping Long Term Evolution operation mode

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An Integrated Scheme to Improve Performance of Fast Mobile IPv6 Handover in IEEE 802.16e Network

An Integrated Scheme to Improve Performance of Fast Mobile I...

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9th IEEE Malaysia International Conference on communications

作者： Seyyedoshohadaei, Seyyed Masoud Khatun, Sabira Ali, Borhanuddin Mohd Othman, Mohamed Anwar, Farhat Department of Computer and Communication System Engineering Universiti Putra Malaysia (UPM) Malaysia Deparment of Communication Technology and Network Universiti Putra Malaysia (UPM) Malaysia Deparment of Electrical and Computer Engineering International Islamic University Malaysia Malaysia

ISBN: (纸本)9781424455324

IEEE 802.16e standard for mobile Worldwide Interoperability for Microwave Access (WiMAX), defines the implementation of hard handover. The standard covers the physical and MAC layer. To apply the layer 3 (L3) handover protocol over the existing IEEE 802.16e layer 2 (L2) handover scheme, the fast mobile IPv6 was used by many researches, but long latency is main challenge for real-time applications. In this paper, to solve latency problem, an integrated scheme is proposed that it combines cross layer design and cross function optimization. The integrated scheme, bases on a pre-establish tunnels concept is dealt both, L2 handover in 802.16e and L3 handover in fast mobile IPv6 to effectively blend the relative messages of L2 and L3. The proposed scheme is compare with the scheme what standardized in IETF network working group (RFC5270). Analytic results prove that the proposed scheme can reduce not only handover latency but also packet losses.

关键词： fast mobile handover handover latency IEEE802.16e packet loss pre-establish tunnel

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Speech disorder malay speech recognition system

Speech disorder malay speech recognition system

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作者： Al-Haddad, S.A.R. Department Computer and Communication System Engineering University Putra Malaysia 43400 UPM Serdang Selangor Malaysia

ISBN: (纸本)9789604741359

Automatic speech recognition systems have the potential to make hard to understand speech more easily recognizable. Designing a system that recognizes impaired speech is more difficult than a system that recognizes normal speech. The Automatic Malay Speech Recognition for Speech Disorder system is able to recognized impaired Malay words spoken by people who suffer from dysarthria, a motor speech disorder resulting from neuron damage, characterized by poor communication. It is developed using techniques used for normal speech recognition but modified to cater for the speech impairment. A feature extraction technique based on the Mel Frequency Cepstrum Coefficient (MFCC) is used along with artificial intelligent algorithms to recognize the speech. In addition, novel pre-processing steps are required to segment the speech prior to recognition taking into account the speech irregularities. The system requires that the user is registered with the system and the system is then trained to accommodate the user speech pattern. The outputs of the system are the visual display of the corrected words uttered or synthesized audio version of the corrected words.

关键词： Speech recognition

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A secure e-auction scheme based on group signatures

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Information systems Frontiers 2009年第3期11卷 335-343页

作者： Lee, Cheng-Chi Ho, Pi-Fang Hwang, Min-Shiang Department of Computer and Communication Engineering Asia University Lioufeng Raod Wufeng Shiang Taichung Taiwan Graduate Institute of Networking and Communication Engineering Chaoyang University of Technology 168 Gifeng E Rd. Wufeng Taichung Country 413 Taiwan Department of Management Information System National Chung Hsing University 250 Kuo Kuang Road Taichung 402 Taiwan

Recently, electronic auctions have been receiving more and more attention in the world of electronic commerce. The security and efficiency of electronic auctions are becoming important. We shall propose a securely sealed-bid auction scheme that uses our group signature scheme with the function of authenticated encryption. It can achieve the following goals: secrecy of bidding price, anonymity, verifiability, non-repudiation, and better performance. © 2008 Springer Science+Business Media, LLC.

关键词： Electronic commerce

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Lattice-reduction-based detector for combined OFDM space division multiple access wireless system

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International Review on computers and Software 2009年第1期4卷 53-57页

作者： Jabir, Amjad N. Khatun, Sabira Noordin, N.K. Ali, Borhanuddin M. Wireless Lab Department of Computer and Communication System Engineering Faculty of Engineering University Putra Malaysia Malaysia of the faculty

Lattice-Reduction-Based detectors have been suggested for multiple input multiple output (MIMO) systems that offer full diversity, yet at the complexity of linear detectors. In this paper, the uplink of a combined OFDM/SDMA system is considered where the base station has multiple antennas while the users have single antenna terminals. The effect of the channel is considered in the frequency domain per OFDM subcarrier and it is shown that for this specific application that gets the benefits of both OFDM and SDMA, a Lattice-Reduction-Based detector is capable also to offer a superior performance, in terms of Bit Error Rate (BER), compared with some of the known detectors. © 2009 Praise Worthy Prize S.r.l. - All rights reserved.

关键词： Space division multiple access

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Stabilization of decision threshold for BER improvement using double carrier modulation/differential detection for outdoor optical wireless communications

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International Review on computers and Software 2009年第3期4卷 301-307页

作者： Hitam, Salasiah Abdullah, Mohd Khazani Adnan, Wan Azizun Wan Sahbuddin, Ratna Kalos Zakiah Department of Computer System and Communication Faculty of Engineering Universiti Putra Malaysia 43400 UPM Serdang Selangor Malaysia

A new transmission and detection technique namely Double Carrier Modulation/Differential Detection (DCM/Diff.D) for outdoor optical wireless (OW) is proposed. The technique employs two beams, one modulated with the data, the other with the inverted version of the same data. A differential detection technique is used at the receiver whereby the inverted data are used as the reference to perform the decision making, as opposed to the fixed threshold used in conventional technique. The probability of error under threshold instability in DCM/Diff.D technique and Intensity Modulation/Direct Detection (IM/DD) technique, is compared. A simulation under heavy rainfall condition of 8.33x10-4 cm/s at bit rate of 2.5 Gbps with 0 dBm of optical transmitter power shows that this technique achieves an improvement of more then twice of distance of the conventional IM/DD. © 2009 Praise Worthy Prize S.r.l. - All rights reserved.

关键词： Decision making

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Context assessment strategies for Ubiquitous Robots

Context assessment strategies for Ubiquitous Robots

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IEEE International Conference on Robotics and Automation (ICRA)

作者： Fulvio Mastrogiovanni Antonio Sgorbissa Renato Zaccaria The Department of Communication Computer and System Science Faculty of Engineering University of Genova Genoa Italy

This paper presents an architecture for context-aware Ubiquitous Robotics applications, where mobile robots cooperate with intelligent environments to fulfill their tasks. Specifically, the work is focused on distributed knowledge representation issues and context assessment strategies, and introduces a technique for on-line context recognition in highly dynamic environments. Experimental validation, performed in a civillian hospital building, is described and discussed.

关键词： Intelligent robots Mobile robots Context awareness Robot sensing systems Intelligent sensors Intelligent actuators Cognitive robotics Robotics and automation Knowledge representation Context modeling

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An improved Malaysian Automatic License Plate Recognition (M-ALPR) system using hybrid fuzzy in C++ environment

An improved Malaysian Automatic License Plate Recognition (M...

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IEEE Conference on Innovative Technologies in Intelligent systems and Industrial Applications (CITISIA)

作者： Khairunnisa Thanin Syamsiah Mashohor Wisam Al-Faqheri Computer and Communication System Engineering Department Universiti Putra Malaysia Serdang Selangor Darul Ehsan Malaysia

In this paper, an improved hybrid fuzzy technique (Fuzzy Logic and Template matching) for Malaysian Automatic License Plate Recognition (M-ALPR) system is proposed. The system is proposed to reduce the program complexity of the existing M-ALPR system and to decrease the processing time of recognizing Malaysian license plates. First, the algorithm to recognize the license plates is presented, by taking advantage of Matlab and C++ programming language benefits in order to increase system efficiency. Feature extraction using vertical line counter is introduced in this system. Later, with the help of OpenCV, the hybrid fuzzy technique is developed using the C++ language. Then, the comparison between these two implementations on M-ALPR system was reported. The improved system was tested on 740 samples images from real scene and the results show that the proposed improvement supports the accurateness and high speed processing of M-ALPR system.

关键词： Licenses Fuzzy systems Character recognition Feature extraction systems engineering and theory Hidden Markov models Neural networks Fuzzy logic Pattern recognition computer vision

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