探测器非线性对可见光通信系统幅频响应的影响

在探测器光电转换效率的理论分析和实际测试结果基础上,建立了其功率电流(P-I)特性的非线性模型。基于该模型分析了探测器工作于线性区和饱和区的光电转换能力,将实际测试结果和理论分析结合,研究了探测器响应度饱和情况下可见光通信系统的幅频响应的变化。实验结果表明在可见光通信(VLC)系统的设计中,荧光粉的余辉虽然不会被高速调制,但是它会降低光电探测器的幅频响应度,由于光功率过大导致的探测器响应度饱和会影响系统的幅频响应幅值和系统带宽。     

LED记忆非线性自适应预失真技术研究

发光二极管(LED)是可见光通信系统(VLC)中最主要的非线性器件,同时由于通带内非平坦的频率响应还伴随着记忆效应。LED的记忆非线性主要恶化了VLC系统的误差矢量幅度(EVM)和比特误码率(BER)。预失真技术通常被用来补偿LED的非线性,从而提高可见光通信系统的性能。现有的预失真技术都不具备自适应性并且没有考虑到LED的记忆效应。提出了一种新的预失真架构,即在发射端增加一路反馈链路来获得LED的输出信号,同时使用记忆多项式模型来自适应地训练并补偿LED的记忆非线性。仿真结果显示提出的预失真技术的BER性能优于现有的方法。     

可见光通信中自适应DFT-spread-OFDM性能研究

综合考虑可见光通信(VLC)中LED灯调制带宽受限及 非线性效应等问题,提出采用离散 傅里叶变换(DFT)-spread-OFDM与自适应调制OFDM相结合的一种自适应DFT-spread-OFDM ,保证通信可靠性的同时, 提高通信速率,通过仿真与实验相结合的方式,研究对比了自适应DFT-spread-OFDM与常 规 DFT-spread-OFDM及常规自适应调制OFDM之间的优劣。仿真和实验结果表明,自适应 DFT-spread-OFDM,能够取得良好的综合性能,较常规DFT-spread-OFDM能够实现更高速 率的通信,较常规自适应调制OFDM能够取得更佳的峰均功率比的(PAPR,peak-average power radio)性能。     

基于多基色LED和OFDM的可见光通信系统

目前,基于单白光LED的光正交频分复用(OFDM)系 统结构的频谱效率(SE)成倍低于传统OFDM系统,为了提高SE,对多基色LED的宽带通信潜能进行了研究,在综合分析经典光OFDM 调制技术的基础 上,提出一种基于多基色LED和OFDM的可见光通信(VLC)系统。系统发射机采用 M基色LED作为发射天线, 并采用OFDM对二进制数据进行调制,调制后的多个复信号再通过二维复信号转 M维实向量信号的方法 和极性编码方法,驱动M基色LED发出复合光信号,接收机采用M 个前端设置有不同颜色滤波器的光 电二极管(PD)接收叠加复合光信号。仿真结果表明,在相同误符号率情况下,本文系统在加 性高斯白噪声环境和 实测信道条件下比经典的非对称限幅光OFDM(ACO-OFDM)的VLC系统大约有2dB的信噪比(SNR)增益。     

适用于可见光通信的LED器件

认为研究发光二极管(LED)器件调制特性以及在高速调制状态下的发光特性是提升新型可见光通信系统性能的关键问题之一,LED器件调制特性的提升可以显著拓展可见光通信系统的应用范围。基于LED器件的调频特性,通过分析发光器件和封装的结构及其他关键光电性能,提出建议:通过降低RC时间以及载流子自发辐射寿命,有效改善LED器件的响应速率,提高LED的调制带宽。     

基于先进调制的高速可见光通信技术

基于发光二极管(LED)调制带宽限制了可见光通信(VLC)系统传输速率这一问题,从VLC系统的先进调制技术出发,探讨了类平衡-正交频分复用、无载波幅相调制和频域均衡单载波调制3种调制技术。对这3种调制技术原理和实验结果的分析与讨论,验证了先进调制技术在提升VLC系统传输容量上的可行性。     

基于FPGA实现的自适应OFDM VLC仿真系统

采用现场可编程门阵列(FPGA)技术搭建了一个自适应正交频分复用(OFDM)可见光通信(VLC)仿真系统。该系统实现了自适应高阶OFDM调制和高速数据速率传输,正交振幅调制(QAM)的调制阶数M有16、64、256、1024四种方式,数据传输速率为16.8~42.0Mb/s。     

一种基于大功率LED照明灯的可见光通信系统

基于强度调制及直接检测(IM/DD)原理,利用18×1 W大功率白光LED照明灯,以开关键控和二进制非归零码(OOK-NRZ)调制方式实现了可见光通信(VLC)系统的室内单向下行通信.为优化LED光源的布局,对光链路视线(LOS)信道损耗进行了理论分析,对LED光源建模并进行光线追迹仿真.系统采用基于TCP/IP的VL...     

可见光通信中的多维编码

为了提高可见光通信(VLC)的频谱利用率,提出一种多维编码方法,从编码原理和性能上进行了理论分析,在此基础上构建了基于RGB发光二极管(LED)的可见光视音频传输系统,并对该编码方法进行了实验验证。实验对多基色LED采用16脉冲位置调制(16-PPM)作为基调制的多维编码方法,在3 m距离上实现了1.5 Mbit/s的视音频数据流传输。结果表明,多维编码方法可以有效利用可见光的宽频谱,提高信道容量,为进一步实现高速通信系统提供了可能。     

基于自适应OFDM的室内可见光通信系统性能研究

为了提高室内可见光通信(VLC)系统性能并充分利用信道带宽资源,将OFDM与自适应技术结合应用于VLC系统中.讨论了系统反馈途径的实现方法,在室内空间环境建模的基础上,对自适应OFDM通信系统的吞吐量和误码率进行了Matlab仿真和分析.     

一种基于激光通信浮标的潜艇水下双工通信方式

对现有潜艇水下通信技术进行比较分析,提出一种采用无线脉冲激光作为通信载波的系留浮标潜艇水下双工通信方式,并简要描述了该通信方式的应用体制及其可行性。     

卫星移动通信系统的发展思考

本文回顾了现代中低轨道卫星移动通信系统的发展历程、在发展过程中存在的问题,全面分析了各行业、部门对卫星移动通信系统的使用需求,并展望未来发展前景,提出了未来卫星全球人个移动通信系统的发展策略。     

Universal personal communications: Emergence of a paradigm shift in the communications industry

It is postulated that today we are in the midst of a major paradigm shift in the communications industry. The essence of this paradigm shift is a transition from today's universal telephone service which has been perfected over the past 100 years, to a future communication service environment, referred to as universal personal communication. Under this new paradigm, communications will be person based in contrast to the predominantly location-based communication environment of today. Societal trends, evolving global standards for communication, regulatory policies, and emergent technologies are seen as the forces driving such a transition. Universal personal communications will be characterized by flexible access to universal services permittingmore enduser control which will result in personalization and customization of such services. Furthermore, the centralized intelligence focus of today's communication networks needs to evolve toward a focus where network intelligence can be migrated to the periphery of the core transport network. The viability of universal personal communication will be critically dependent upon how well it addresses the end customer value proposition. Two key elements of this proposition are transparency of mobility and personalization of service environments. A zonal service environment model which classifies and characterizes these various service environments in terms of common communication parameters is proposed. This model is built around hierarchical structures for both cellular and digital wireless transmission, and can be viewed as critical towards the realization of transparent mobility management and personalization of services.     

无线上网新技术——WAP

Ｉｎｔｅｒｎｅｔ和移动通信已经在全球迅猛发展,无线上网成为必然趋势,ＷＡＰ论坛所制定的ＷＡＰ协议充分应用Ｉｎｔｅｒｎｅｔ的思想,支持多种目前及将来的无线网络,寿命用户在移动中使用各种目前仅在有线方式下方可使用的服务。本文介绍了ＷＡＰ的技术背景、设计思想和系统结构,并分析了ＷＡＰ对业界和人们的影响。     

ACTS MOBILE TERMINALS

The development of the advanced communications technology satellite (ACTS) mobile terminal (AMT) and its follow-on, the broadband aeronautical terminal (BAT), have provided an excellent testbed for the evaluation of K- and Ka-band mobile satellite communications systems. Such systems have proved viable for many different commercial and government applications. Combining emerging satellite communications technologies such as ACTS' highly focused spotbeams with the smaller, higher-gain K- and Ka-band antenna technology, results in system designs that can support significantly higher throughput capacity than today's current commercial systems. An overview of both of these terminals is presented in this paper.     

发展中的VSAT技术

介绍ＶＳＡＴ最新技术及发展趋势。帮助用户合理规划和选用ＶＳＡＴ系统。     

我国光纤通信系统传输设备产业现状与发展建议

光纤通信在中国已有20余年的发展史，拥有大量的科研成果，但尚未能形成产业。建议高度重视其问题，把关系国家命脉的信息控制和管理权掌握在自己手中。     

Experimental detection of mobile satellite transmissions with cyclostationary features

One of the important functions of cognitive radio (CR) technology is spectrum sensing. The implementation of an efficient spectrum sensing function can be quite challenging because of various factors such as multi‐path fading, low signal‐to‐noise ratio of the radio communication services to be detected and the requirement to detect and analyze the signal in a short time. As a consequence, it is important to quantitatively assess the performance of spectrum sensing techniques in various scenarios. This paper investigates different digital signal processing techniques for spectrum sensing in the context of mobile satellite transmissions: power sensing, cyclostationary sensing, efficient cyclostationary sensing based on FFT accumulation method and strip spectral correlation algorithm. This paper presents experimental results on the cyclostationary properties of GSM Thuraya mobile satellite communications in various conditions both for the uplink and downlink channels. The receiver operating characteristics are computed, and the results are presented for different algorithms and different positions of the satellite terminals. The experimental results show that the cyclostationary‐feature‐based detection can be robust compared to energy‐based technique for low signal‐to‐noise ratio levels. Copyright © 2014 John Wiley & Sons, Ltd.     

采用MT—TCM的跳频／扩频多址系统的性能研究

本文采用不降低扩频处理增益的多音网格编码调制（ＭＴ－ＴＣＭ）及改进的交织ＭＴ－ＴＣＭ方案来提高跳频／扩频多址系统的性能，对于给定的总跳频带宽，跳束和符号速率，考虑加性白高斯噪声，部分带宽干扰与多有户干扰的综合影响，推导出估计比特错误率的计算公式。给出数值与模拟结果，并与采用卷积编码的跳频／扩频多址系统的性能作了比较。     

移动数据：开创移动服务新天地

固定网数据业务的发展经历将在移动网上重演,其发展潜力将更大于固定网;充分重视短消息业务是运营商将来生存和发展的重要基础;移动Ｉｎｔｅｒｎｅｔ是移动数据发展的必然趋势;日本ｉＭＯＤＥ移动上网的成功策略给人们很多启示。