Wide illumination and communication angle visible light communication system based on low output impedance LED driver amplifier

The visible light communication (VLC) system employs large viewing divergence angle light-emitting diode (LED) to realize illumination and communication simultaneously, so the geometric loss of optical power may reach tens of decibels, moreover, considering the gain reduction of the LED at high frequency, signal power at the receiver will be too weak. To overcome these drawbacks, in this paper, a low output impedance power driver amplifier is presented to provide enough power to drive a medium power commercial LED used at the end of the optical transmitter. A 125 Mbit/s real-time communication with illumination and communication angle of 130° has been achieved at a distance of 3 m, the bit error rate (BER) is 3.13×10-11 at a divergence angle of LED of 0° and 1.21×10-6 at a communication angle of 130°. Experimental results indicated that this VLC system can be used for illumination and communication simultaneously.     

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.     

室内VLC白光LED调制带宽拓展

针对室内照明场景应用需求,探究了驱动电流的变化对四种常用LED光源频率特性所产生的影响效果,得出荧光粉LED的频率特性响应几乎不受驱动电流变化的影响的结论。结合硬件预均衡策略对1 W荧光粉LED的调制带宽拓展进行了理论分析和硬件电路设计,测试结果表明:在不对蓝光过滤的条件下,荧光粉LED调制带宽由1 MHz提高到了32 MHz,单盏荧光粉LED在非归零-开关键控（non-return-to-zero on-off-keying,NRZ-OOK）调制下可达到26 Mbit/s的传输速率,误码率7.5510-6,传输距离达到3 m,符合于室内照明通信对传输距离的要求。     

BER performance analysis of an OFDM-based visible light communication system using DHT post-coding

The theoretical analysis of the bit error rate(BER) performance in a discrete Hartley transform(DHT) post-coded orthogonal frequency division multiplexing(OFDM) visible light communication(VLC) system over an additive white Gaussian noise(AWGN) channel is presented. The theoretical analysis results show that the proposed DHT post-coding scheme does not degrade the BER performance of the post-coded OFDM VLC systems. The analysis result is confirmed by our simulation results for random bit source....     

Numerical analysis on an OOK-NRZ visible light communication system based on a single white LED

An OOK-NRZ visible light communication (VLC) system is designed by using a single white LED and a 550 nm visible photodetector. The emitting model of the single LED is established, and the general expression of the detector’s output signals under OOK modulation is deduced. With the selected LED, detector and other related parameters, the designed communication system is optimized and its performance is analyzed. The optimized communication distance between the LED and the detector is 0.54 m at the communication bit rate of 1 Mbit/s. With the best communication distance, when the signal-to-noise ratio (SNR) is larger than 6.5 dB, the bit error rate (BER) can drop to 10-4. The analytical model and theory presented in this paper can be of certain practical meanings in the design of similar communication systems.     

日盲紫外LED实时视频传输系统设计

针对当前紫外光通信中气体灯与激光光源调制速率慢、体积较大,光电倍增管工作电压过高等问题,提出了一种基于现场可编程门阵列技术的日盲紫外LED实时视频传输系统,其发射光源采用波长为265 nm的单紫外LED,探测器采用紫外PIN;通过电路和逻辑模块设计搭建了视频传输系统,研究了系统的光功率密度与通信距离之间的关系;基于二进制开关键控调制方式,实现日盲紫外LED实时视频传输系统最大传输速率为2.88 Mbit/s,当通信距离为4 m时,传输速率达到1.92 Mbit/s。     

Channel capacity of the distributed MIMO relay in visible light communication systems

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.     

500 Mbit/s transmission experiment using 1.3 ?m wavelength InGaAsP/InP high-speed surface-emitting DH LEDs

A 1.3 ?m-wavelength high-speed surface-emitting DH LED, with 0.6 ns rise time and 1.3 ns fall time, has been developed by optimal design of both the LED parameters and driving circuit. A 500 Mbit/s RZ pseudorandom pulse transmission experiment using the high-speed DH LED has been performed with a 5.7 dB level margin over a 2.7 km optical fibre. The 500 Mbit/s LED system feasibility has been confirmed.     

基于双重调制技术的可见光通信系统研究

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。     

A real-time VLC to UART protocol conversion system

A real-time visible light communication(VLC) to universal asynchronous receiver/transmitter(UART) conversion system is made up of a transmitter with a light emitting diode(LED) and a receiver with a photodiode(PD), by which a VLC system is connected to traditional communication modes, and the data are transferred by wireless visible light. UART packets are converted to light packets by the modulation of a 10 k Hz on-off-keying(OOK) light signal, and the data losses in the transportation are avoided by the protection of a data buffer mechanism. The experimental results reveal that the real-time VLC to UART conversion system can provide a real-time VLC transmission way for two UART devices in not less than 10 m at a baud rate not less than 19 200 Bd with stable ambient lighting at the same time.     

Visible light communication application scenarios based on Android smart devices’ LED lamp

Visible light communication (VLC), which uses visible light to achieve wireless communication just as its name implies, transmits information mainly through the high-speed light flashing of LED or fluorescent lamp. And it has many advantages, such as high security, high energy efficiency, and long life expectancy. In recent years, the application of smart devices based on the Android system is becoming more and more abundant. If the VLC is combined with smart devices based on Android system, we will have a wide range of application scenarios in the future. In this paper, by using LED lamps as the transmission side, two methods of different Android mechanisms to make the flicker in different data rate are presented. By optimizing the code framework, using new function in the hardware driver layer, the operating efficiency can be increased greatly, and the maximum data rate of 5000 bps on the Android development board is achieved. In the meantime, due to the LED’s features and experiments’ result, we give two flowcharts of application scenarios: the mobile payment and ships communication.     

基于可见光通信的一对多视频广播系统

利用自主研发的软硬件搭建了基于可见光通信(VLC )的一对多视频广播系统。通过传输流(TS,transport stream)音视频数据流解决了通信信道 不可靠的问题,通过广播流量控制算法和控制指令的设计解决了多媒体数据广播传输时服务 器和客户端速率不匹配带来的超大缓存需求问题。可见光收发模块采用荧光型LED和PIN探测 器作为光源和探测器。系统拥有蜂窝网络结构,每个蜂窝可以有多个用户,客户可以同时接 收广播信号且不会相互干扰。通过实验实验证了系统的可行性。测试结果表明,本文系统支 持1对多的1080P视频数据光学无线广播传输,每个用户的接收带宽为 2Mbit/s,传输距离为2m。     

基于无线可见光通信的双向语音对讲系统

设计并实现了基于无线可见光通信(VLC)的双向语 音对讲系统。上下行链路均使用普通的1W发光二极管(LED)手电筒作为发射端光源, 同时实现语音传输和照明功能。系统采用开关键控-非归零码(OOK-NRZ)调制方式,在测 试LED的光电特性后,设计了LED 驱动电路和接收电路;使用单片机控制音频编解码芯片实现语音信号的采集、处理和传输, 通过异步收发传输接口(UART) 进行数据传输,实现了最远通信距离为40m、最高传输速率为2.5Mbit/s的全双工实时语音 对讲。本文系统实现复杂度低、成 本低和功耗小,并可应用于其他数据传输场合,具有良好的实用性和广泛的适用性。     

PLC和VLC融合的车厢内宽带视频服务系统

电力线通信(Power Line Communication,PLC)可以为LED灯提供照明功率的同时作为骨干网为可见光通信(VisibleLight Communication,VLC)馈入信息,具有很好的应用前景.提出了一个基于PLC和VLC融合的车厢内宽带视频服务系统,详细描述了该系统的结构和框架、关键技术参数,测试了演示系统的关键通信性能,讨论了未来的应用方向,可为新一代列车车厢内部的综合信息服务和通信系统提供一定的指导和参考.     

Performance study of an OFDM visible light communication system based on white LED array

By introducing orthogonal frequency division multiplexing (OFDM) technology, a visible light communication (VLC) system using a 5x5 white LED array is studied in this paper. The OFDM transmitter and receiver are modeled through MATLAB/Simulink tool. The electrical-optical-electrical (EOE) response of the VLC channel, which is also the response of the detector, is derived based on Lambert’s lighting model. Then the modeling on the overall OFDM/VLC system is established by combining the above three models together. The effects of the factors which include the digital modulation, Reed-Solomon (RS) coding, pilot form, pilot ratio (PR) and communication distance on the bit error rate (BER) of the system are discussed. The results show that through the use of RS coding, block pilot, quadrate phase shift keying (QPSK) modulation and a suitable pilot ratio about 1/3, under the communication rate about 550 kbit/s, the BER can be dropped to below 10-5, and the communication distance can reach 0.9 m.     

Half‐duplex visible light communication using an LED as both a transmitter and a receiver

In typical visible light communication (VLC) systems, light‐emitting diodes (LEDs) are used as optical transmitters and photodiodes are used as optical receivers. Currently, many communication devices such as smart phones have a built‐in LED lamp whereas they usually do not have a built‐in photodiode. If we find a way to receive VLC signals without the need to add an additional photodiode on the communication devices, it will contribute to the spread of VLC. Therefore, we propose and demonstrate a VLC scheme without the need for a photodiode. As the first step, we investigate the characteristics of an LED as a VLC receiver and find out that an LED can also be used as a VLC receiver in certain conditions. Then, we demonstrate a half‐duplex VLC system using an LED as both an optical transmitter and an optical receiver, without the need for a photodiode. This technique could be used in various applications such as the VLC between smart phones with a built‐in LED lamp and the VLC between LED traffic lights. Copyright © 2015 John Wiley & Sons, Ltd.     

Master-slice monolithic integration design and characteristics of LD/LED transmitters for 100-400 mbit/s optical transmission systems

Monolithic integration of LD and LED transmitters operating at 100-400 Mbit/s is investigated using a 3-μm Si-bipolar process as a first step in the establishment of a master-slice IC technology for optical communication systems. An LD transmitter IC is developed as a master IC, which includes a differential current switch and an input buffer circuit for high-speed modulation and a current stabilizer and an APC circuit for the stabilization of the output optical power, An LED transmitter is fabricated by the minor change of wiring of the master IC. The former exhibits 0.5-ns rise and 0.7-ns fall times at the signal current of 40 mA. Also the latter exhibits 0.4-ns rise and 0.6-ns fall times at the signal current of 100 mA. Characteristics of LD and LED transmitters are estimated in order to prove the usefulness of the fabricated IC's. As a result, it is confirmed that both transmitters using the fabricated IC's operate at the modulation speed of 300-400 Mbit/s and output optical power fluctuations of less than ±0.5 dB over the ranges of 5V ±5 percent supply voltage and 0-50°C temperature. From these results, it is proven that the master-slice monolithic integration is feasible and will be very useful for reduction of the turn-around time in IC development.     

1 Gbit/s high-speed bit-synchronisation LSI for B-ISDN

The CCITT recommended that the bit rates for synchronous digital hierarchy (SDH) should be multiples of 155.52 Mbit/s. In handling high-speed data (such as 622.08 Mbit/s) in B-ISDN switching systems, there are problems associated with waveform degradation caused by impedance mismatching and amplitude attenuation. A countermeasure is the regeneration of the distorted waveforms using the system clock in each board. A bit-synchronisation circuit allows distorted waveforms to be regenerated and simplifies the design of timing between boards. The author have developed a high-speed bit-synchronisation LSI with excellent jitter tolerance in the 600 Mbit/s region and which has a simple circuit structure. The LSI features a circuit structure based on an elastic store, Si-bipolar super self-aligned process technology (SST),/sup 1/ and careful timing design. It can handle three different bit-rates (622.08, 155.52, and 51.84 Mbit/s) and has a maximum bit rate of 1 Gbit/s.<>     

DFT-spread combined with clipping method to reduce the PAPR in VLC-OFDM system

Orthogonal frequency division multiplexing (OFDM) is an attractive technique to realize high data rate in light emitting diodes (LEDs)-based visible light communication (VLC). However, high peak-to-average power ratio (PAPR) of OFDM makes VLC-OFDM very sensitive to the nonlinearity of LEDs. In this paper, the discrete Fourier transform-spread (DFT-spread) combined with clipping method is proposed to reduce the PAPR of OFDM signal in VLC system. Combining simulation with experiment, a performance comparison is made among conventional OFDM, DFT-spread-OFDM, and clipped DFT-spread-OFDM with different clipping ratios (CRs) in a single LED-based VLC system. The experimental results show that the proposed clipped DFT-spread-OFDM method can effectively improve the system performance compared with the other two methods. At the optimum signal peak-to-peak (PTP) value, by using the clipped DFT-spread-OFDM scheme with CR at 8 dB, the bit error rate (BER) of the system can be reduced from 0.003 7 to 0.000 287. E-mail:dengrui189@126.com      

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。