共查询到18条相似文献,搜索用时 171 毫秒
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基于预失真四进制辐移键控调制的可见光通信系统 总被引:5,自引:5,他引:0
白光LED不仅可以用来照明还可以作为通信系统的光源,近年来随着光电器件性能的提高,室内可见光通信系统的研究成为热点。但照明用白光LED受自身器件特性限制,有效带宽仅为1MHz,为了在有限的带宽内提高通信速度和通信质量,设计了一种预失真的四进制辐移键控(4ASK)调制方案。在系统的发射端采用RC均衡和预失真电路,用以缓解LED带宽不足的情况;通过模拟实验得到最优化的参数后,搭建了可见光通信(VLC)传输系统的硬件电路。实验结果表明,在1m的传输距离内,系统最快传输速率可达到20MHz/s,误码率(BER)小于10-6。 相似文献
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偏置电流对LED内部温度、结电阻和载流子浓度产生的变化导致LED频率响应发生改变。分析了偏置电流对LED频率响应的影响机理以及对调制带宽的影响规律,并通过测试平台进行了测试验证。结果表明:红、绿、蓝LED工作在额定功率以下时,偏置电流与调制带宽基本处于线性正比关系,在接近和超过额定功率时,调制带宽变化缓慢并最终趋于稳定。偏置电流对荧光粉LED的调制带宽几乎没有影响。此研究对可见光通信系统偏置电流的选取及均衡电路的设计提供参考。 相似文献
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白光LED灯几MHz到几百MHz的调制带宽使其在照明的同时兼具通信功能。首先提出了照度均方差最小化准则来设计LED灯在室内的布局问题,分别考虑了不包含墙壁反射和包含墙壁反射两种情况下对室内照度分布的影响,分别给出了两种情况下白光LED灯的最优布局。然后分析了室内视距链路(不包含墙壁反射)和非视距链路(包含墙壁反射)下的室内照度分布、接收功率分布以及信噪比分布。非视距链路相对于视距链路来说,室内照度分布和接收功率分布明显增加,但是信噪比明显下降,这主要是由于非视距链路下墙壁反射产生的码间干扰所致。 相似文献
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荧光粉浓度和电流强度对白光LED特性的影响 总被引:4,自引:0,他引:4
讨论了荧光粉浓度及驱动电流强度对白光LED特性的影响。采用软件模拟实验和实际封装测试相结合的研究方法进行分析研究。对荧光粉浓度变化对白光LED光通量和相关色温(CCT)的影响进行了三维光线追迹模拟,并且进行了实际的封装验证。另外对白光LED的节温和显色性也做了深入细致的研究。研究结果表明:CCT随着荧光粉浓度的增大而减小,光通量则先上升后下降。同时由荧光粉浓度和驱动电流强度变化所引起的节温升高会降低荧光粉的转换效率。对显色性而言,采用高浓度荧光粉封装的白光LED有相对低的显色指数;并且显色指数随着驱动电流强度的增加而升高,最终趋于稳定。 相似文献
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驱动电流对大功率白光LED荧光粉转换效率的影响 总被引:4,自引:2,他引:2
对4种1W白光功率LED进行了100~900mA的变驱动电流光学特性试验。分析了荧光粉转换效率随驱动电流变化的内在机理,一是由于驱动电流增大导致蓝光芯片内量子限制斯塔克效应引起峰值波长蓝移,致使蓝光与荧光粉的匹配程度降低;二是由于驱动电流增大导致器件温度升高,荧光粉的非辐射增多,且其激发态能级分裂加剧,导致部分能量降低,黄光波长出现红移现象。通过分析上述两种因素的综合作用,得出了荧光粉转换效率随驱动电流变化的规律,并据此提出改进白光LED驱动电流特性的建议。 相似文献
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基于双重调制技术的可见光通信系统研究 总被引:2,自引:1,他引:1
LED调制带宽制约着可见光通信(VLC) 系统的数据传输速率。为此,提出一种基于双重调制技术COB(chip on board)封装 的LED灯具,通过实现16级脉冲振幅 调制(PAM),将系统数据传输速率提升4倍;结合脉冲宽度调制(PWM)技术 进行调光,同时兼顾室内的照明及通信。采用Matlab软件模拟仿真视频传输试 验。结果表明,在相同信噪比(SNR)的情况下,基于双重 调制技术的VLC系统的误码率(BER)比传统使用开关键控(OOK)调控技术系 统的BER更低。本文系统在不增加器件带宽前提下,成倍提高了无线通信的 质量与 数据传输速率;从照明与通信的角度优化了VLC系统的信源,具有广阔的 应用前景。 相似文献
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荧光粉发光LED作为白光光源在照明领域有着广泛的应用。长时间工作,荧光粉发光LED将出现色温偏移现象。荧光粉发光LED的色温偏移与芯片衰减和荧光粉衰减有关。提出了一种能同时考虑芯片衰减和荧光粉衰减的数学模型。从理论上分析了芯片衰减和荧光粉衰减对荧光粉发光LED的色坐标及色温变化的影响。提出了一种利用蓝光LED与荧光粉发光LED混合,通过对蓝光LED进行负反馈控制,保证蓝光辐射在全白光中的辐射功率比值恒定,从而实现色温稳定的白光LED照明系统。 相似文献
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荧光粉转换白光LED具有高能效、低成本、长寿命等优势,广泛应用于照明领域,提高荧光粉转换白光LED的光效一直是该领域的研究热点。为了对白光LED的高性能封装进行设计优化和制备,采用模拟仿真以及实验测试相结合的方式,对LED芯片封装进行研究分析,采用了特制支架和双芯片封装,提高灯珠光效,在此基础上,改进了荧光粉涂覆工艺,提高了荧光粉激发效率,整体提高LED光效约6%,且研究了远程荧光粉与芯片的距离变化时LED的光效变化。 相似文献
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Visible light communication (VLC) technology is a new type of wireless communication technology, which employs a light source as the carrier of information to realize illumination and communication simultaneously. This paper adopts a single InGaN/GaN-base multi-quantum well blue micro-light emitting diode (LED) as the light source, designs pre-emphasis circuit, LED driver circuit, impedance matching network, etc., and builds a high-speed real-time VLC system. It has been verified that the LED achieves a 3 dB modulation bandwidth of 450 MHz or more; and the real-time communication rate reaches over 800 Mbit/s at a distance of 2 m. The communication bit error rate (BER) is as low as at a communication rate of 622 Mbit/s. Experimental indicators including 3 dB bandwidth, communication rate, and communication BER are all taken into account. Therefore, this VLC system supports high-quality high-speed real-time communication. 相似文献
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Visible light communication (VLC) is a novel paradigm that uses light-emitting diode (LED) light as an information carrier and has several advantages over radio-frequency communication in terms of the bandwidth, security and multi-path fading. When the VLC system is considered in an indoor environment, LED lamps, which are placed at the ceiling to provide ambient light, can offer rich spatial resources for VLC as distributed intermediate relaying terminals. This paper introduces a novel distributed multiple-input multiple-output (D-MIMO)-relaying VLC scheme and analyzes its communication performance. Using the sum rate of the broadcasting and multiple access relay channels, a tight upper bound on the channel capacity was derived. The numerical results showed that the D-MIMO-relaying VLC scheme outperformed the direct-path-based scheme in terms of the channel capacity. For a given indoor environment, the capacity of D-MIMO-relaying VLC can be improved further by selecting the appropriate relay parameters, such as the number of LED–PD pairs in a relay, distance between relays and height of relays. 相似文献
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Design and experiment of post-equalization for OOK-NRZ visible light communication system 总被引:4,自引:0,他引:4 下载免费PDF全文
Considering that the white LED’s spectral response decreases exponentially with the increase of carrier frequency for the on-off-keying non-return-to-zero (OOK-NRZ) visible light communication (VLC) data links, a first-order RC high-pass filter is designed and fabricated as a post-equalizer (PE) to compensate the LED spectral response. Formulation and simulation are both available for illustrating the VLC performance with and without PE. Experiments are performed in detail for the fabricated OOK-NRZ VLC system integrated with PE. The data transmission results show that by using PE, the measured carrier bandwidth is enhanced from 0.8 (0.4-1.2) MHz to 1.7 (0-1.7) MHz, and the bit-error-rate (BER) is less than 10-9. It proves the feasibility of the proposed scheme in OOK-NRZ VLC data links. 相似文献
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Visible light communication (VLC) system has been becoming a potential technology for short‐range data communication over wireless optical channel. In this paper, a real‐time state‐of‐the‐art VLC system prototype is implemented mainly based on enhanced subcarrier index modulation orthogonal frequency division multiplexing (ESIM‐OFDM) modulation scheme. The prototype has been designed using NI cDAQ hardware equipment programmed in matlab /labview . In other words, the developed VLC transceiver labview model is loaded into cDAQ to perform real‐time transmission of text data. The design mainly comprises VLC transmitter, VLC receiver, interfacing NI cDAQ with labview , and implementation of ESIM‐OFDM. It should be noted that the direct output of ESIM‐OFDM is not suitable to drive VLC transmitter circuit; therefore, the key contribution lies in making use of sigma–delta modulator to modify ESIM‐OFDM output to produce constant current signal which in turn could drive VLC transmitter. The second main contribution of the work targets the luminous properties of the designed transmitter that have experimentally been characterized using a LUX meter. Finally, the last contribution of the work is the simulation carried out to analyze the performance of the proposed system with other existing VLC modulation schemes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献