NB-IoT物理层上行链路通信技术解析

NB-IoT作为物联网的主要技术,以其容量低、覆盖广、成本低和低功耗等优点在智慧城市建设中扮演着重要角色。主要从频率部署、上行传输方案、上行链路帧结构和上行物理信道几个方面解析,以便让读者更了解NB-IoT技术的物理层上行链路。     

基于OLED的可见光通信实验性能研究

基于有机发光二极管(Organic Light-Emitting Diode,OLED)发光的基本原理与特性,设计了一种适用于OLED的可见光通信均衡电路。实验探究OLED的光照度随驱动电流和空间距离变化的特性、伏安特性和频率响应,并与LED相关特性做对比,绘制特性变化曲线,给出对比实验结果。测得实验所用UIV牌OLED的3 dB带宽约为85 kHz,验证了OLED作为光源进行可见光通信的可行性,为开设物联网通信创新性、研究性实验教学项目提供了方案。     

基于白光LED的可见光通信技术研究

可见光通信是基于白光LED的新兴无线光通信技术,能够同时实现照明和通信的双重功能,适合在智能家居等领域的应用。本文对基于白光LED的室内可见光通信的研究现状及关键技术、发展趋势进行了研究。     

中国发展可见光通信技术与产业的思考

认为随着固体照明技术在世界范围的广泛应用,可见光通信已引起学术界和产业界高度关注,并逐渐取得小部分市场,但要真正大规模应用,还需综合考虑技术演进规律,并在国家和地方政府政策扶植下,加强产学研合作,共同推进LED信息化技术应用进程。     

多光源可见光通信关键技术

可见光通信技术主要基于发光二极管（light emitting diode,LED）,依托现有照明网络基础设施完成信息传输与组网。针对室内多灯照明场景,研究了照明约束下的星座图优化与功率资源优化;并结合光学智能反射表面,动态调控反射信道,以提升系统传输数据率与覆盖范围。同时,通过初步研究,揭示了低频调制光信号的频闪效应对人体的影响,意味着LED光生物效应需要在未来的信号设计中全面考虑。     

国外空间激光链路通信技术进展

对空间激光链路通信技术的形式和优点进行了分析,详细介绍了美国、西欧、日本等发达国家在空间激光通信领域的发展历史和发展趋势,给出了上述各国家主要研究机构在该领域试验时采用的技术、系统、设备及主要工作指标。     

基于波分复用技术的LED可见光通信的研究北大核心

介绍了LED(发光二极管)可见光通信系统和波分复用技术的原理,利用Optisystem软件设计了波分复用技术在可见光通信链路传输中的系统结构,实现了光路百兆级的实时通信。采用直接调制方式,对NRZ(非归零)码和RZ(归零)码调制方式下的传输性能进行了对比研究,分析了不同速率对系统的误码率和Q因子等因素的影响,进而讨论了在不同传输距离下系统误码率的变化特性,验证了波分复用技术应用在LED可见光通信系统中的可行性和稳定性。     

用于VLC的LED半功率角优化布局方法研究

提出通过优化发光二极管(LED)半功率角的布局来提高室内可见光通信系统性能的方法。4种典型的LED布局方式的仿真结果表明,该方法对于提高可见光通信系统的信噪比、降低信噪比的波动有明显效果。对于均匀的LED布局方式,信噪比的波动从未优化时的5.2 d B大幅下降到0.3 d B。该方法不需要调节LED的功率,更适合于工程运用。     

基于可见光通信的室内光电混合网络组网关键技术

针对可见光通信在室内的应用,分析了采用可见光与无线射频构成光电混合网络的可行性,提出了一种可行的网络架构;指出了该网络架构组网中的关键技术问题,并针对网络中的光源布局、多址接入、小区切换、异构网络融合等给出了技术路线。     

基于垂直结构GaN LED的水下蓝光通信系统

垂直结构GaN LED能够提高器件的出光效率和调制带宽,是可见光通信的关键器件。该文面向水下蓝光通信的重大应用需求,基于亚波长理想LED模型,设计、制备了垂直结构蓝光LED器件,在NRZ-OOK调制下可实现10 Mbps的无线光通信。该文进一步搭建了水下可见光通信系统,采用基于该器件,实现了调制速率2 Mbps的全双工水下蓝光通信。     

基于副载波复用的多输入单输出正交频分复用LED可见光通信系统

提出了一种基于副载波复用的新型的多输入单输出(MISO)正交频分复用可见光通信(OFDM-VLC)系统构架,并且实验验证了2×1和3×1的MISO OFDM-VLC系统传输。分别测量了2×1和3×1的实验系统的误差矢量幅度(EVM)随输入电压变化的曲线图,找出了两个系统各自的最佳偏置范围。在将输入电压设置在最佳偏置范围之内的情况下,改变传输距离,对2×1系统,给出了系统EVM性能变化的曲线图;对3×1系统,给出了系统EVM和误码率(BER)性能变化的曲线图。在没有任何均衡的情况下,两个系统的传输距离都可以长达140cm。     

A High-Speed Bi-Directional Visible Light Communication System Based on RGB-LED

In this paper, we propose and experimentally demonstrate a bi-directional indoor communication system based on visible light RGB-LED. Spectrally efficient modulation formats （QAM-OFDM）, advanced digital signal processing, pre- and post- equalization are adopted to compensate the severe frequency response of indoor channel. In this system, we utilize red-green-blue Light emitting diodes （LEDs）, of which each color can be used to carry different signals. For downlink, the low frequencies of each color are used while for uplink, the high frequencies are used. The overall data rate of downlink and uplink are 1.15-Gb/s and 300-Mb/s. The bit error ratios （BERs） for all channels after 0.7 m indoor delivery are below pre-forward- error-correction （pre-FEC） threshold of 3.8×10-3. To the best of our knowledge, this is the highest data rate in bi-directional visible light communication system.     

LED非线性对基于正交频分复用可见光通信系统的影响

基于带有寄生参数的发光二极管(LED)Shockley方程,结合具有饱和特性的固态功率放大器的幅度传输模型,构建了可见光通信系统中LED的双向饱和非线性模型。基于该模型,通过蒙特-卡洛仿真分析了LED非线性对采用正交频分复用(OFDM)的可见光通信系统(VLC)性能的影响。分析结果表明OFDM的VLC系统性能受LEDI-V特性非线性、直流偏置电压、基带调制方式、调制信号切顶比率及方式的直接影响。     

OFDM-FDMA Scheme for the Uplink of a Mobile Communication System

The Orthogonal Frequency Division Multiplexing (OFDM) transmission technique can efficiently deal with multi-path propagation effects especially in broadband radio channels. It also has a high degree of system flexibility in multiple access schemes by combining the conventional TDMA, FDMA and CDMA approaches with the OFDM modulation procedure which is particularly important in the uplink of a multi-user system. In OFDM-FDMA schemes carrier synchronization and the resulting subcarrier orthogonality plays an important role to avoid any multiple access interferences (MAI) in the base station receiver. An additional technical challenge in system design is the required amplifier linearity to avoid any non-linear effects caused by a large peak-to-average ratio (PAR) of an OFDM transmission signal. A specific OFDM-FDMA uplink procedure is proposed and will be designed in this paper which can be seen as a combination of a specific subcarrier spreading scheme and subcarrier selection process. The resulting transmit signal consists of a periodic extension and multiple repetition of all modulation symbols and leads therefore to an extremely low computation complexity in the transmitter. Furthermore, the transmit signal shows simultaneously a constant envelope to avoid any non-linear effects in the amplification process. This uplink scheme can be considered as a trade off between low computation complexity and system performance. Prof. Hermann Rohling is with the Technical University Hamburg-Harburg, Germany where he has developed an international reputation in the field of OFDM transmission techniques. Previously Prof. Rohling was with the AEG Research Institute, Ulm as a researcher working in the area of digital signal processing for radar and communications applications. His research interests have included Wideband Mobile Communications especially based on Multicarrier Transmission Techniques (OFDM) for future broadband systems (4G), signal theory, digital radar signal processing, detection, estimation and differential GPS for high precision navigation. Prof. Rohling is a member of Informationstechnische Gesellschaft (ITG), German Institute of Navigation (DGON) and a senior member of IEEE. He is chairman of the August 2005 International OFDM Workshop (InOWo 2005) in Hamburg, Germany. Martin Stemick received the Dipl.-Ing. degree in electrical engineering from the Technical University Hamburg Harburg (TUHH), Germany in 2004. Currently, he is a Ph. D. student and belongs to the scientific staff of the Department of Telecommunications, TUHH, Hamburg, Germany. His research interests include wireless OFDM-systems, with a current emphasis on resource allocation and equalization techniques.     

基于彩色二维条码流的Display-to-Camera通信系统

为了满足人们的多元化通信需求,构建可靠的低成本通信链路,本文利用日常生活中的屏幕显示设备和照相摄像设备,构建了新型Display-to-Camera通信系统.描述了系统基本链路并建立系统模型,阐述了收发机实现框架和关键技术;搭建实验系统,设计了符合显示屏显示特性的新型彩色条码流,用以承载信息;接收端利用计算机图像处理技术,匹配、跟踪识别信号区域,过滤系统背景噪声;利用帧分类和颜色增强技术抑制了系统符号间干扰,保证了彩色条码的正确识别.实验系统实现了速率287kbit/s的数据传输,解码正确率99.8%.