Performance enhancement of IM/DD optical wireless systems

Due to the fast development of telecommunications and the great demand of bandwidth, optical wireless communication (OWC) has become a promising trend. OWC offers flexible networks for both indoor and outdoor communications providing high security, high speed and a license free spectrum. Data transmission over indoor OWC systems with diffused channel model at high speed will extend the channel impulse response over several symbol periods with many reflections causing inter-symbol interference. This interference distorts the data symbols being transmitted and affects the signal recovery at the receiver side. This paper studies error control coding for OWC systems over additive white Gaussian noise and ceiling bounce channel models. It considers Hamming coding and channel equalization for unipolar optical orthogonal frequency division multiplexing (OFDM) system. The objective is to mitigate the channel distortion, and hence achieve reliable transmission and correct detection at the receiver side.     

Efficient coding techniques for ADO-OFDM in IM/DD systems

Optical wireless communication (OWC) is an age-long technology, which is based on optical data transmission through free space, and it can be implemented in both indoor and outdoor applications. Asymmetrically clipped DC-biased optical orthogonal frequency division multiplexing (ADO-OFDM) is a modulation scheme that can be utilized in indoor OWC systems. It is based on transmitting DC-biased optical OFDM (DCO-OFDM) for even-frequency subcarriers and asymmetrically clipped optical OFDM (ACO-OFDM) for odd-frequency subcarriers. The ADO-OFDM exhibits better optical power performance than those of the conventional ACO-OFDM and DCO-OFDM. The main disadvantage of ADO-OFDM is the clipping noise, which mainly affects the even subcarriers. So, in this paper, convolutional and turbo coding techniques are investigated to improve the bit error rate performance of the ADO-OFDM over Additive white Gaussian noise and diffuse channels. Simulation results show that the proposed coded ADO-OFDM using convolutional and turbo coding techniques achieves significantly lower BERs compared to that of the uncoded ADO-OFDM. In addition, turbo-coded ADO-OFDM gives the best BER performance.     

无线光互连技术发展综述

人们对无线宽带通信技术的需求在近些年稳步增长.无线电波频谱的带宽限制和频带拥堵,通过微波无线网络的发展已经有了明显的改善.然而,无线光互连技术才能使得数据传输带宽达到理想的要求.作为许多无线通讯系统的最终方案,无线光互连也被选择为长期的解决策略.并且,无线光互连的大量优势还没有得到完全的发掘,许多基础性和应用性的研究还需要在实验层面和商业应用层面加以深入.国外,Gb/s的无线光传输已经在实验室中得到了验证,然而,可用的室内无线光互连系统也仅仅达到了155Mb/s的速度.下面将着重从收发系统、性能及安全性方面对无线光互连技术作一概况阐述.     

Advances and prospects in visible light communications

Visible light communication (VLC) is an emerging technology in optical wireless communication (OWC) that has attracted worldwide research in recent years. VLC can combine communication and illumination together, which could be applied in many application scenarios such as visible light communication local area networks (VLANs), indoor localization, and intelligent lighting. In recent years, pioneering and significant work have been made in the field of VLC. In this paper, an overview of the recent progress in VLC is presented. We also demonstrate our recent experiment results including bidirectional 100 Mbit/s VLAN or Li-Fi system based on OOK modulation without blue filter. The VLC systems that we proposed are good solutions for high-speed VLC application systems with low-cost and low-complexity. VLC technology shows a bright future due to its inherent advantages, shortage of RF spectra and ever increasing popularity of white LEDs.     

探测通信一体的自组织泛在无线网络体系架构探讨

针对跨平台协同共享的网络中心体系化协同作战要求,文中瞄准海上无线网络体系建设宏观要求,结合当前无线网络技术、频谱分享、孔径综合和探通一体技术发展成果,提出探通一体的自组织泛在无线网络体系框架设想,从网络架构和拓扑、终端接入能力、定向组网技术、无线资源分配、QoS 管理、多域资源跨层调度优化、网络安全等方面,分析了技术挑战和可能的实现途径,展望了预期成效和应用前景。     

Enhanced Optical Wireless Communication System for Bio-signal Monitoring Applications

Wireless Personal Communications - In this paper, optical wireless communication (OWC) technology based mobile remote care unit is proposed. Since, the existing RF based medical systems are suffer...     

Impact of pointing errors and turbulence effects on POLSK and coherent OWC-based FSO system over generalized turbulence channel model

The emerging technology in wireless communication, free space optics (FSO) offers a myriad of merits over current radio frequency links due to its wide license-free bandwidth, ease of installation, high security features and viable cost for short-distance communication. Its unparallel high-speed data rate and immunity against electromagnetic interference makes FSO the emerging technology of today. Atmospheric conditions like absorption, scattering, turbulence and pointing error prevail during wireless transmission. Through this paper we aim at elucidating the effect of the error introduced by misalignment between the transmitter and receiver that are ideally required to be in the line of sight rendering pointing error. Pointing error and turbulence effects are the main limitation parameters for our analysis. For this purpose, we have taken into consideration three different modulation techniques polarization shift keying, coherent OWC and on–off keying FSO communication system. We derived the novel expressions for the average spectral efficiency (ASE) over the generalized turbulence model for these modulation techniques. The ASE is analyzed against average transmitted optical power with the maximum ASE of 50 bits/s/Hz at the transmitted power of 10 dBm for coherent OWC technique.     

利用自适应均衡滤波器改善大气湍流信道OWC性能

光无线通信是近年来无线通信领域的研究热点之一。大气湍流是影响光无线通信的重要因素,特别是在高速数字通信中会产生严重的码间干扰。本文分析了大气湍流信道的特性,提出采用自适应LMS均衡技术改善大气湍流信道的性能,对采用OOK调制方式的OWC系统均衡前后的误码率性能进行了分析比较。仿真结果表明自适应LMS均衡技术可以将系统的性能提高约10dB。     

基于SCA无线通信系统的安全体系结构研究

采用软件无线电技术和模块化设计思路,构造新一代的无线通信系统,是无线通信发展的趋势。介绍了软件通信体系结构(SCA)的无线通信系统,描述了基于SCA无线通信系统的安全体系结构,详细分析了加密子系统、信息安全子系统和设备安全子系统。这样定义的安全体系结构保证了基于SCA无线通信系统实现不同的安全模式,提供不同的安全级别。     

Transmit Beamforming for MIMO Optical Wireless Communication Systems

This paper focuses on transmit beamforming for multiple-input multiple-output optical wireless communication (OWC) systems with intensity modulation and direct detection (IM/DD). OWC with IM/DD requires the transmitted signals to be nonnegative, for which existing beamforming schemes developed for radio frequency systems cannot be applied directly. We propose effective schemes for OWC over frequency flat and frequency selective channels. For frequency flat fading, the property of the beamforming vector is derived. For frequency selective fading, bit-error rate performances of the proposed scheme with zero-forcing and minimum mean-square error frequency domain equalization receivers are derived, and a suboptimal beamforming vector for frequency selective fading channels is proposed. Compared with asymmetrically clipped optical orthogonal frequency division multiplexing based frequency domain beamforming, the proposed scheme needs much less feedback information and has a better error performance.     

白光LED照明的可见光通信的现状及发展

用室内照明的白光LED光源作为通信基站进行信息无线传输的技术是当前国外光无线通信领域的研究热点之一,是一项有发展前景的新兴技术.文章详细介绍了白光LED照明的室内可见光通信技术在国内外的研究现状,分析了其关键技术,阐述了其发展趋势.     

Secure group communication in wireless mesh networks

Wireless mesh networks (WMNs) have emerged as a promising technology that offers low-cost community wireless services. The community-oriented nature of WMNs facilitates group applications, such as webcast, distance learning, online gaming, video conferencing, and multimedia broadcasting. Security is critical for the deployment of these services. Previous work focused primarily on MAC and routing protocol security, while application-level security has received relatively little attention. In this paper we focus on providing data confidentiality for group communication in WMNs. Compared to other network environments, WMNs present new challenges and opportunities in designing such protocols. We propose a new protocol framework, Secure Group Overlay Multicast (SeGrOM), that employs decentralized group membership, promotes localized communication, and leverages the wireless broadcast nature to achieve efficient and secure group communication. We analyze the performance and discuss the security properties of our protocols. We demonstrate through simulations that our protocols provide good performance and incur a significantly smaller overhead than a baseline centralized protocol optimized for WMNs.     

Optical wireless multiple-input multiple-output system based on avalanche photodiode receiver

With the rising demand for high data-transmission rates, optical wireless communication (OWC) is considered one of the particularly appropriate solutions. In this paper, an avalanche photodiode (APD)-based optical wireless configuration is used to approximate the receiver output. This paper also presents bit error rate (BER) evaluation statistics compared with the theoretical results for optical wireless multiple-input multiple-output (MIMO) communication systems. In particular, the simulated results show that the BER of a 4 × 4 MIMO system is significantly lower than that of other APD systems (over 10 times better when the mean energy is higher than − 165 dBJ). To summarize, the OWC-MIMO system shows enormous potential in the high-speed data-transmission field.     

浅析下一代移动通信网络的安全问题

随着移动通信网络的不断发展,无线接人技术、终端技术、网络技术和业务平台技术正向异构化、多样化和泛在化的趋势发展。下一代移动通信网络具有开放、灵活、可管理、移动的网络架构特点,因此其安全问题将比以往移动通信系统更加复杂。文章从下一代移动通信网络的组网结构人手,结合第二代及第三代移动通信系统存在的安全问题,分析下一代移动通信网络所面临的安全威胁,论述了其应具有的安全体系结构。     

海洋光学系统中的时空方法

海洋光学系统在海洋探索、开发和监测中起到了越来越重要的作用。水下无线光通信、水下激光雷达是两种迅速发展且有良好应用前景的海洋光学系统。水下无线光通信凭借高速率与低延迟的特点在中短距离应用中成为理想的通信选择;水下激光雷达在获取地理信息、目标探测等应用中也是常用的高精度、高效率的观测方法。然而,海水信道的复杂光学特性为海洋光学系统性能的进一步提升带来了挑战。在海水信道中,不仅吸收与散射作用较强,而且信道中可能有湍流、气泡等动态变化的干扰因素。为应对这些挑战,一方面可通过时间或空间方法提高信噪比;另一方面,时空信息转换的方法有利于提升系统的性能。文中对以上解决方案进行综述,并指出海洋光学系统的发展趋势。     

基于最小均方自适应滤波器的无线光通信接收性能分析

无线光通信(OWC)系统采用大气通道作为传输媒介,而大气湍流效应引入了与信号强度有关的乘性噪声。为了消除乘性噪声所引起的信号衰落,分析并给出了基于最小均方(LMS)自适应滤波器的判决门限更新算法和稳态的抽头权系数相关矩阵算法。通过理论分析和计算机仿真,讨论了最小均方滤波器及其参数对无线光通信接收性能的影响。结果表明,采用非因果滤波器的无线光通信系统对湍流噪声具有明显的抑制作用。在弱湍流情况下,基于自适应最小均方滤波器的系统误码率(BER)低于10-8,可以满足网络通信的要求。通过分析不同滤波器阶数对误码率的影响表明,所采用的255阶的非因果结构的最小均方滤波器是最优的结构。     

Transporting data between wireless applications using a messaging system—MMS

There is a demand for using messaging systems to transport data between wireless applications in mobile communications. As multimedia messaging service (MMS) is a promising messaging system to meet the demand, it is under enhancement in related standardization bodies to make it effective in transporting application data. The enhancement should be compatible with the existing MMS services for its smooth and safe deployment. This paper proposes a solution to make the enhancement backward compatible, so that a new MMS service of transporting application data has no impact on the existing MMS services. The solution also provides forward compatibility, so that an MMS service of transporting application data does not hinder the introduction of any application in the future, allowing instantaneous deployment of a wireless application. The standardization bodies did not define any format for data communication between a wireless application and MMS in a terminal. A common format in this regard would help mass availability of wireless applications for different purposes independent of manufacturing a mobile terminal. Based on an analysis described in this paper, eXtensible Markup Language (XML) is the suitable format for the purpose. This paper also presents examples of XML file to indicate what data should be communicated in this regard. Copyright © 2006 John Wiley & Sons, Ltd.     

光无线技术设计与应用

光无线系统技术结合了无线通信的可移动性和光通信的高容量的优点,阐述了光无线信道的特性和对发射器,接收器的设计考虑;介绍了几种短距离光无线系统,并对其发展进行了展望。     

基于LDPC码和BPPM的无线光通信系统性能研究

为了克服光在弱湍流大气条件传输时,光强闪烁造成的突发错误,在已知信道衰落信息(CSI)和未知信道衰落信息(NCSI)条件下,研究了基于低密度奇偶校验(LDPC)码和二进制脉冲位置调制(BPPM)的无线光通信系统性能,论述了BPPM光通信信道对称性的特点,并与基于LDPC码和OOK调制的光通信系统性能进行了比较。结果表明,在NCSI和CSI情况下,基于LDPC码和BPPM的光通信系统相对于基于LDPC码和OOK调制的系统均有更优异的差错性能;在NCSI情况下,基于LDPC码和BPPM的光通信系统的性能相对于CSI情况下的系统性能损失并不大;且采用LDPC码BPPM相对于LDPC码OOK调制的光通信系统,随着湍流强度的增大系统性能损失较小。因此,基于LDPC码和BP-PM的光通信系统在不需要信道衰落信息估计的情况下,能获得较大的编码增益,便于工程实现,在无线光通信中将有一定的应用前景。     

无线自组网络在应急通信中的研究与应用

本文提出一种无线自组网络的应用和设计方法,目的是解决应急通信中存在的自动组网、自动修复、快速部署等困难,实现传送现场实时高清视频和语音通话。本文通过对无线自组网络的创新设计,在不依赖任何通信网络基础设施的情况下提供了一种通信支撑环境,在公安执法、森林防火、抢险救灾、军队演练、反恐特勤、野外考察、地下作业等领域有广泛的应用。