Table of Content

    01 April 2016, Volume 14 Issue 2
    Special Topic
    Optical Wireless Communications
    GONG Chen,TANG Xuan, WANG Xiaodong
    2016, 14(2):  1-1. 
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    Subcarrier Intensity Modulated Optical Wireless Communications:A Survey from Communication Theory Perspective
    Md Zoheb Hassan, Md Jahangir Hossain, Julian Cheng, Victor C M Leung
    2016, 14(2):  2-12.  doi:10.3969/j.issn.1673-5188.2016.02.001
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    Subcarrier intensity modulation with direct detection is a modulation/detection technique for optical wireless communication systems, where a pre-modulated and properly biased radio frequency signal is modulated on the intensity of the optical carrier. The most important benefits of subcarrier intensity modulation are as follows: 1) it does not provide irreducible error floor like the conventional on-off keying intensity modulation with a fixed detection threshold; 2) it provides improved spectral efficiency and supports higher order modulation schemes; and 3) it has much less implementation complexity compared to coherent optical wireless communications with heterodyne or homodyne detection. In this paper, we present an up-to-date review of subcarrier intensity modulated optical wireless communication systems. We survey the error rate and outage performance of subcarrier intensity modulations in the atmospheric turbulence channels considering different modulation and coding schemes. We also explore different contemporary atmospheric turbulence fading mitigation solutions that can be employed for subcarrier intensity modulation. These solutions include diversity combining, adaptive transmission, relay assisted transmission, multiple-subcarrier intensity modulations, and optical orthogonal frequency division multiplexing. Moreover, we review the performance of subcarrier intensity modulations due to the pointing error and synchronization error.
    Short-Range Optical Wireless Communications for Indoor and Interconnects Applications
    WANG Ke, Ampalavanapillai Nirmalathas, Christina Lim, SONG Tingting, LIANG Tian, Kamal Alameh, Efstratios Skafidas
    2016, 14(2):  13-22.  doi:10.3969/j.issn.1673-5188.2016.02.002
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    Optical wireless communications have been widely studied during the past decade in short-range applications, such as indoor high-speed wireless networks and interconnects in data centers and high-performance computing. In this paper, recent developments in high-speed short-range optical wireless communications are reviewed, including visible light communications (VLCs), infrared in-door communication systems, and reconfigurable optical interconnects. The general architecture of indoor high-speed optical wireless communications is described, and the advantages and limitations of both visible and infrared based solutions are discussed. The concept of reconfigurable optical interconnects is presented, and key results are summarized. In addition, the challenges and potential future directions of short-range optical wireless communications are discussed.
    Optimal Transmission Power in a Nonlinear VLC System
    ZHAO Shuang, CAI Sunzeng, KANG Kai, QIAN Hua
    2016, 14(2):  23-28.  doi:10.3969/j.issn.1673-5188.2016.02.003
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    In a visible light communication (VLC) system, the light emitting diode (LED) is nonlinear for large signals, which limits the transmission power or equivalently the coverage of the VLC system. When the input signal amplitude is large, the nonlinear distortion creates harmonic and intermodulation distortion, which degrades the transmission error vector magnitude (EVM). To evaluate the impact of nonlinearity on system performance, the signal to noise and distortion ratio (SNDR) is applied, defined as the linear signal power over the thermal noise plus the front end nonlinear distortion. At a given noise level, the optimal system performance can be achieved by maximizing the SNDR, which results in high transmission rate or long transmission range for the VLC system. In this paper, we provide theoretical analysis on the optimization of SNDR with a nonlinear Hammerstein model of LED. Simulation results and lab experiments validate the theoretical analysis.
    Modulation Techniques for Li-Fi
    Mohamed Sufyan Islim, Harald Haas
    2016, 14(2):  29-40.  doi:10.3969/j.issn.1673-5188.2016.02.004
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    Modulation techniques for light fidelity (Li-Fi) are reviewed in this paper. Li-Fi is the fully networked solution for multiple users that combines communication and illumination simultaneously. Light emitting diodes (LEDs) are used in Li-Fi as visible light transmitters, therefore, only intensity modulated direct detected modulation techniques can be achieved. Single carrier modulation techniques are straightforward to be used in Li-Fi, however, computationally complex equalization processes are required in frequency selective Li-Fi channels. On the other hand, multicarrier modulation techniques offer a viable solution for Li-Fi in terms of power, spectral and computational efficiency. In particular, orthogonal frequency division multiplexing (OFDM) based modula-tion techniques offer a practical solution for Li-Fi, especially when direct current (DC) wander, and adaptive bit and power loading techniques are considered. Li-Fi modulation techniques need to also satisfy illumination requirements. Flickering avoidance and dimming control are considered in the variant modulation techniques presented. This paper surveys the suitable modulation techniques for Li-Fi including those which explore time, frequency and colour domains.
    LDPC Decoding for Signal Dependent Visible Light Communication Channels
    YUAN Ming, SHA Xiaoshi, LIANG Xiao, JIANG Ming, WANG Jiaheng, ZHAO Chunming
    2016, 14(2):  41-46.  doi:10.3969/j.issn.1673-5188.2016.02.005
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    Avalanche photodiodes (APD) are widely employed in visible light communication (VLC) systems. The general signal dependent Gaussian channel is investigated. Experiment results reveal that symbols on different constellation points under official illuminance inevitably suffer from different levels of noise due to the multiplication process of APDs. In such a case, conventional log likely-hood ratio (LLR) calculation for signal independent channels may cause performance loss. The optimal LLR calculation for decoder is then derived because of the existence of non-ignorable APD shot noise. To find the decoding thresholds of the optimal and suboptimal detection schemes, the extrinsic information transfer (EXIT) chat is further analyzed. Finally a modified minimum sum algorithm is suggested with reduced complexity and acceptable performance loss. Numerical simulations show that, with a regular (3, 6) low-density parity check (LDPC) code of block length 20,000, 0.7 dB gain is achieved with our proposed scheme over the LDPC decoder designed for signal independent noise. It is also found that the coding performance is improved for a larger modulation depth.
    A Survey on Event Mining for ICT Network Infrastructure Management
    LIU Zheng, LI Tao, WANG Junchang
    2016, 14(2):  47-55.  doi:10.3969/j.issn.1673-5188.2016.02.006
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    Managing largescale complex network infrastructures is challenging due to the huge number of heterogeneous network elements. The goal of this survey is to provide an overview of event mining techniques applied in the network management domain. Event mining includes a series of techniques for automatically and effectively discovering valuable knowledge from historical event/log data. We present three research challenges (i.e., event generation, root cause analysis, and failure prediction) for event mining in network management and introduce the corresponding solutions. Event generation (i.e., converting messages in log files into structured events) is the first step in many event mining applications. Automatic root cause analysis can locate the faulty elements/components without the help of experienced domain experts. Failure prediction in proactive fault management improves network reliability. The representative studies to address the three aforementioned challenges are reviewed and their main ideas are summarized in the survey. In addition, our survey shows that using event mining techniques can improve the network management efficiency and reduce the management cost.
    Research Paper
    Review of AVS Audio Coding Standard
    ZHANG Tao, ZHANG Caixia, ZHAO Xin
    2016, 14(2):  56-62.  doi:10.3969/j.issn.1673-5188.2016.02.007
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    Audio Video Coding Standard (AVS) is a second-generation source coding standard and the first standard for audio and video coding in China with independent intellectual property rights. Its performance has reached the international standard. Its coding efficiency is 2 to 3 times greater than that of MPEG-2. This technical solution is more simple, and it can greatly save channel resource. After more than ten years’ development, AVS has achieved great success. The latest version of the AVS audio coding standard is ongoing and mainly aims at the increasing demand for low bitrate and high quality audio services. The paper reviews the history and recent develop-ment of AVS audio coding standard in terms of basic features, key techniques and performance. Finally, the future development of AVS audio coding standard is discussed.
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    The whole issue of ZTE Communications April 2016, Vol. 14 No. 2
    2016, 14(2):  0. 
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