Visible Light Communications - current challenges and ... · LiFi communication - a complementary technology to the wireless fidelity (WiFi), where illumination and high-speed communication

Visible Light Communications -current challenges and prospects

2020 10TH EDITION OF ADVANCED TOPICS IN OPTOELECTRONICS, MICROELECTRONICS AND NANOTECHNOLOGIES CONFERENCE 1

Alina-Elena Marcu*,

Robert-Alexandru Dobre*,

Marian Vlădescu*

*ELECTRONIC TECHNOLOGY AND RELIABIL ITY DEPARTMENT,

POLITEHNICA UNIVERSITY OF BUCHAREST, ROMANIA

al [email protected]

As time passes, the optical wireless communication systems (OWC) areseeing more and more technological advancement. The completereplacement of conventional lighting with LED based solutions seemsto be in sight. Technology and its development always match theworld's current needs, and as the whole economy is shifting towardsecology and sustainability, moving towards low consumption LEDswould seem to be a good approach. The LED's ability to switch on andoff at a fast rate enables the possibility of developing new opticalcommunication systems. In Visible Light Communication (VLC)systems, the LEDs represent the transmitter and the photodetectorsrepresent the receiver. A similar technology to VLC, known as OpticalCamera Communications (OCC) uses image sensors as the receiver. Thepaper investigates the performances of different OWC technologiesand provides a detailed overview of the areas and applications inwhich they can be found.


INTRODUCTION❑ The technologies that are part of OWC are Visible Light Communication (VLC), Optical

Camera Communications (OCC), Free Space Optical Communication (FSOC), LightDetection and Ranging (LiDAR) and Light Fidelity (LiFi).

❑ VLC systems - illumination and communication can be provided simultaneously,

❑ OCC systems - a noninterference communication can be provided,

❑ FSOC systems - high-data-rate communication can be handled over large distances,

❑ LiDAR systems - the information about a remote target, as well as the range can be found,

❑ LiFi communication - a complementary technology to the wireless fidelity (WiFi), whereillumination and high-speed communication can be provided simultaneously.

Optical Wireless Communication Systems

Visible Light

Communication

Optical Camera

Communications

Free Space Optical

Communication

Light Detection

and RangingLight Fidelity

Spectrum type Visible lightVisible, and

infrared light

Visible, near-

infrared, and

ultraviolet light

Near-infrared,

visible light

Visible, infrared,

and ultraviolet light

Transmitter

type

LED or

Laser diode (LD) LED LD LD LED

Receiver type Photodetector Image Sensor Photodetector Photodetector Photodetector

Applications

Aviation,

Hospitals, Indoor

localization

Intelligent

Transport System

Inter-chip

connectivity,

Underwater

communication

Meteorology,

Architectural

surveys

Smart infrastructure

connected with

cloud


The use of LEDs for lighting and communication began in 2000 when researchers at Keio University in Japan proposed the use of white LEDs in homes to build an access network. This was further fueled by rapid research, especially in Japan, to build high-speed communication through visible light with the development of VLC support for portable devices and transport vehicles.

This lead to the formation of the VLCC (Visible Light Communications Consortium) in Japan in November 2003, to publicize and standardize the VLC technology. The VLCC proposed three standards that were accepted by Japan Electronics and the Japan Electronics and Information Technology Industries Association (JEITA) as JEITA CP-1221, JEITA CP-1222 and JEITA CP-1223.

The first IEEE standard for visible spectrum communication was proposed in 2011 as IEEE 802.15.7, supporting data rates from 11.67 kb/s to 96 Mb/s.

In 2014, the VLCA (Visible Light Communications Associations) is established as the successor to the VLCC in Japan for further standardization of VLC.

INTRODUCTION


❑ In VLC communication, the LEDs are used as transmitters andphotodetectors are used as receivers.

❑ Data is transferred by the rapid change of the light intensity of the LEDs,change that must be very fast to prevent the perception of the flickering ofthe light by the human eye and also allow high data rate.

❑ Compared to classic radio communication systems, VLC has the followingadvantages:

❑ increased security compared to radio waves, which creates electromagneticinterference, therefore it is dangerous in hazardous operations,

❑ the energy is used more efficiently,

❑ using light instead of radio waves benefits from a wider bandwidth, withoutcausing environmental harm.

❑ There are a few disadvantages: VLC requires field-of-view alignment andline-of-sight clearance between the transmitter and the receiver.

VISIBLE LIGHT COMMUNICATION SYSTEMS


❑ The biggest difference between the VLC system and the radio frequencysystem is that in VLC, the data cannot be encoded in the phase oramplitude of the light signal. This means that phase and amplitudemodulation techniques cannot be applied in VLC, and the information mustbe encoded in the variation of the emitted light wave intensity.

❑ The various modulation schemes that can be used in the visible lightcommunication are:

❑ On-Off Keying (OOK) - data bits “1” and “0” are transmitted by repeatedlyturning the LED off and on,

❑ Pulse Width Modulation (PWM) - the encoded information is transmitted in theduration of a pulse,

❑ Pulse Position Modulation (PPM) - data is encoded using the pulse position in aframe,

❑ Variable Pulse Position Modulation (VPPM) - the bits are encoded by choosing adifferent pulse position as in the case of PPM modulation and the pulse width canalso be changed as needed,

❑ Color Shift Keying (CSK) - by combining different colors of light, the output datacan be carried by the same color and thus the output intensity can be constant,

❑ Orthogonal Frequency Division Multiplex (OFDM) - the VLC channel is divided intoseveral orthogonal subcarriers and the data is sent in parallel sub-streamsmodulated per subcarrier.



❑ A complementary type of communication, known also as Optical CameraCommunications (OCC), can be achieved by using image sensors as receivers,with the advantage being the possibility of receiving information transmitted bymultiple individual LEDs.

❑ The solutions available use as receivers high frame rate cameras, over 800frames per second, that are very expensive. In this case, the receiver’s designcould be simplified, as the luminous signal can be oversampled using currenttechnology.

❑ A cost-effective solution would be using low frame rate cameras but that has adisadvantage: it requires auxiliary synchronization between the image frameand the timing of the transmitted symbol.

❑ Recently, OCC solutions using low frame rate cameras have been proposed thatalso don’t require auxiliary synchronization between the transmitter and thereceiver. The human eye does not perceive the LED’s flicker, due to the highspeed in which the code controlled transmitter switches the LED’s light on andoff. Furthermore, no auxiliary synchronization between transmitter and receiveris required, as the latter is able to detect transmitted symbols and synchronizeitself with the received data sequence, without relying on the shutter effect ofCMOS sensors.




APPLICATIONS

Aviation

passenger media services

Hospitals

where conventional radio waves could cause interference with

medical equipment

Indoor localization applications

helping track moving objects in real-time through LED beacons

and a camera facing upward

Smart displaying signboards

integrating information about the timetable of transportation

vehicle or shops detectable using the smartphone’s camera

Advertisement light panels

provide information such as product details, or a contact

address for more details, to the user’s smartphone via its camera.

Museums

the light used on exhibits can also transmit ID information sent periodically to be scanned by

visitors’ smartphones.

Automotive

reduce traffic and increase safety

❑ Although, VLC has advantages as visible light spectrum is not regulated, being license-free and wider than the Radio Frequency (RF) spectrum, use LED being easy to implement in the current lighting solutions, high energy efficient, do not create electromagnetic interference (EMI), faces many challenges.


DISCUSSION AND CHALLENGES

Affordability

Line of sight

Flickering

ISO noise

Synchronization

Dimming

control

CONCLUSIONS

❑ The paper investigates different OWC technologies and provides a detailed overview of the areas and applications in which the visible light communication and optical camera communications systems can be found.

❑ Though the domain is relatively new, it has the potential to overcome some of the difficulties found in various domains, i.e., in aviation, hazardous environments, hospitals, indoor localization, automotive. These technologies can also be paired with 5G communication to enable further expansion of future IoT applications.

❑ Various challenges have also been tackled in VLC and mentioned in the proposed article (affordability, line of sight, flickering, dimming control, synchronization and noise).


Visible Light Communications - current challenges and ... · LiFi communication - a complementary technology to the wireless fidelity (WiFi), where illumination and high-speed communication

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