An enhanced method for dynamic characterization of high-power LEDs for visible light communication applications

Visible light communications (VLC) have been proposed for several applications beyond the traditional indoor scenarios, from vehicular to underwater communications. The common element in all these applications is the use of light-emitting diodes (LEDs) in which the forward current that flows through each LED plays a major role. Therefore, knowing the electrical equivalent of the LEDs is a useful tool for the proper design of the VLC systems. Currently, some measurement instruments exist, such as the LCR (inductance, capacitance, and resistance) meters or impedance analyzers to characterize the main parameters of the LEDs. However, these instruments and measurement procedures are subject to satisfying some requirements, such as a minimum value of the input impedance or the maximum forward current. In this work, the LED LXHL-BW02 is used to obtain its equivalent circuit, using different measurement methods and traditional methods of measurement with our proposed method. The equivalent model is implemented on the simulation tool LTSPICE. Our alternative method can be used for determining the electrical equivalent circuit of LEDs subject to high current variations at very high frequencies, in the MHz range, i.e., in an operating range for VLC applications.This research was co-financed by Comunidad de Madrid and the FSE/FEDER Program under grant SINFOTON2-CM (S2018/NMT-4326), the Madrid Government (Comunidad de Madrid) under the Multiannual Agreement with UC3M in the line of “Fostering Young Doctors Research” (GEOVEOLUZ-CM-UC3M), and in the context of the V PRICIT (Regional Programme of Research and Technological Innovation, and the Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-109072RB-C31) and under the CDTI (Centre for the Development of Industrial Technology, Ministerio de Ciencia e Innovación) throughthe European Regional Development Fund (ERDF) EXP 00119337/IDI-2019029

Дослідження процесів передачі сигналів в безпроводовому оптичному тракті з використанням GNU Radio

Мета роботи полягає в тому, щоб провести огляд технології VLC, її переваг, основних характеристик та створити стенд для досліджень передачі з використанням видимого світла.The aim of the work is to review the VLC technology, its advantages, main characteristics and to create a stand for research of transmission using visible ligh

Design and implementation of a bi-directional visible light communication testbed

Abstract. This work defines a bi-directional visible light communication (VLC) testbed design and implementation process using Universal Software Radio Peripheral (USRP) software defined radios (SDR) and open-source software. The visible light communication design uses LED light sources for wireless communications purposes. The testbed combines light, infrared and radio frequencies as wireless media to be utilized in a hybrid wireless communication system. Bi-directional communication at 12.5 Mbps bit rate was successfully achieved and only limited by a sample rate of the USRP system. The achieved communication distance was in the range of 0.5 to 7 meters depending on the used optics. A TCP-IP communication and access to the Internet was also established by using light and infrared communication links. The Internet connection was also established by using power line communication for providing data to the lighting through the existing power line cables. The results in the work were obtained by using a GMSK modulation. Also, GFSK, QPSK, 8-PSK, 16-QAM and OFDM modulation were initially tested for future study.Kaksisuuntaisen näkyvän valon tiedonsiirtotestialustan suunnittelu ja toteutus. Tiivistelmä. Työssä suunnitellaan ja rakennetaan kaksisuuntainen kokeiluympäristö valon käyttöön langattomassa tiedonsiirrossa käyttäen ohjelmistoradioita ja avoimen lähdekoodin ohjelmistoja. Kokeiluympäristössä voidaan tutkia ja käyttää valon, Infrapunan ja radioaaltojen taajuusalueita tiedonsiirtoon. Valon tiedonsiirrossa käytetään valaistuskäyttöön suunniteltuja LED valaisimia sekä valaistukseen että tiedonsiirtoon. Työssä saavuttiin laitteiston näytteistystaajuuden rajoittama kaksisuuntainen 12,5 Mb/s tiedonsiirtonopeus ja käytetyn optiikan ominaisuuksista sekä tiedonsiirtonopeudesta riippuvainen tiedonsiirtoetäisyys 0,5–7 metriä. Järjestelmään ohjelmoitiin valo- ja infrapunalinkin avulla toimiva TCP-IP yhteys Internetiin. Internet yhteys valaisimelle onnistuttiin siirtämään myös käyttäen sähköverkon valmiita kaapelointeja. Työn tulokset saavuttiin käyttäen GMSK moduloitua signaalia. Myös GFSK, QPSK, 8-PSK, 16-QAM ja OFDM modulaatioiden toimivuus testattiin tutkimuksen jatkoa varten

Моделі каналів передачі даних в мережі LiFi

Актуальність теми: Зараз зі збільшенням даних постає питання в збільшенні пропускної здатності безпроводових мереж. Рішенням цієї проблеми може слугувати реалізація мережі LiFi. Реалізація може бути як в сукупності з іншою радіочастотною мережею для розвантаження даних, так і автономно – в обох випадках потреба в високій швидкості передачі даних буде задоволена. Але для досягнення цієї мети варто вирішити низку питань, одним із яких є вибір оптимального каналу передачі даних. Метою роботи є опис моделей каналів в мережі LiFi. Об’єкт дослідження – технологія LiFi. Предмет дослідження – канали мережі LiFi. Методи дослідження – MathCAD, Adobe Photoshop. Наукова новизна роботи полягає в пропонуванні альтернативного рішення реалізації каналу VLC на базі 6G.Relevance of the topic: Now, with the increase in data, there is a question of increasing the bandwidth of wireless networks. The solution to this problem can be the implementation of a LiFi network. The implementation can be both in combination with another radio frequency network for data offloading, and autonomously - in both cases, the need for high data transmission speed will be satisfied. But in order to achieve this goal, it is necessary to solve a number of issues, one of which is the choice of the optimal data transmission channel. The purpose of the work is to describe channel models in the LiFi network. The object of research is LiFi technology. The subject of research is LiFi network channels. Research methods – MathCAD, Adobe Photoshop. The scientific novelty of the work consists in offering an alternative solution for implementing the VLC channel based on 6G

Investigation and Implementation of Dicode Pulse Position Modulation Over Indoor Visible Light Communication System

A visible light communication (VLC) system with green technology is available and enables users to use white LEDs for illumination as well as for high data rate transmission over wireless optical links. In addition, LEDs have advantages of low power consumption, high speed with power efficiency and low cost. Therefore, a great deal of research is considered for indoor VLC, as it offers huge bandwidth whilst using a significant modulation technique. This thesis is concerned with the investigation and implementation of the dicode pulse position modulation (DiPPM) scheme over a VLC link using white LED sources. Novel work is carried out for applying DiPPM over a VLC channel theoretically and experimentally including a comparison with digital PPM (DPPM) in order to examine the system performance. Moreover, a proposal of variable DiPPM (VDiPPM) is presented in this thesis for dimming control. The indoor VLC channel characteristics have been investigated for two propagation prototypes. Two models have been proposed and developed with DiPPM and DPPM being applied over the VLC channel. A computer simulation for the proposed models for both DiPPM and DPPM systems is performed in order to analyse the receiver sensitivity with the effect of intersymbol interference (ISI). Both systems are operating at 100 Mbps and 1 Gbps for a BER of 10-9. An improvement in sensitivity being achieved by the DiPPM compared to the DPPM VLC system. The system performance has been carried out by Mathcad software. The predicted DiPPM receiver sensitivity outperforms DPPM receiver at by -5.55 dBm and -8.24 dBm, at 1 Gbps data rate, and by -5.53 dBm and -8.22 dBm, at 100 Mbps, without and with guard intervals, respectively. In both cases the optical receiver sensitivity is increased when the ISI is ignored. These results based on the received optical power required by each modulation scheme. Further work has been done in mathematical evaluation carried out to calculate the optical receiver sensitivity to verify the comparison between the two systems. The original numerical results show that DiPPM VLC system provides a better sensitivity than a DPPM VLC system at a selected BER of 10-9 when referred to the same preamplifier at wavelength of 650 nm and based on the equivalent input noise current generated by the optical front end receiver. The results show that the predicted sensitivity for DPPM is greater than that of DPPM by about 1 dBm when both systems operating at 100 Mbps and 1 Gbps. Also, it is show that the receiver sensitivity is increased when the ISI is limited. Experimentally, a complete indoor VLC system has been designed and implemented using Quartus II 11.1 software for generating VHDL codes and using FPGA development board (Cyclone IV GX) as main interface real-time transmission unit in this system. The white LEDs chip based transmitter and optical receiver have been constructed and tested. The measurements are performed by using LED white light as an optical transmitter faced to photodiode optical receiver on desk. Due to the LED bandwidth limitation the achieved operating data rate, using high speed LED driver, is 5.5 Mbps at BER of 10-7. The original results for the measurements determined that the average photodiode current produced by using DiPPM and DPPM optical receivers are 8.50 μA and 10.22 μA, respectively. And this in turn indicates that the DiPPM receiver can give a better sensitivity of -17.24 dBm while compared to the DPPM receiver which gives is -16.44 dBm. The original practical results proved the simulation and theoretical results where higher performance is achieved when a DiPPM scheme is used compared to DPPM scheme over an indoor VLC system

Testbed for Experimental Characterization of Indoor Visible Light Communication Channels

In this paper, we describe an experimental testbed designed to evaluate indoor visible light communications (VLC) in realistic scenarios. The system is based on a mockup where the location and orientation of the optical receiver can be modified with precision for a static configuration of walls and ceiling lamp arrangements. The system utilizes a timing synchronization method, which is based on evaluating the training sequence periods used for channel response estimation, which enables robust frame synchronization. In addition, an adaptive rate orthogonal frequency-division multiplexing (OFDM) scheme is used to assess the VLC performance throughout the receiver plane emulating a real communication. The preliminary results obtained with this prototype, considering a multiple-input single-output (MISO) scenario, demonstrate that reflection on walls yields a significant increase in data rates, which can be additionally improved if appropriate orientation of the receiver is implemented. However, vertical orientation upward of the optical receiver still constitutes a simple solution but efficient enough. Moreover, a good agreement between simulation and experimental results is observed, which confirms the suitability of the mockup as an experimental testbed for practical evaluation of indoor VLC systems, where system performance for different lamp arrangements and receiver designs, including multi-user communications, can be studied