The document discusses the conceptual design and experimental setup of a Visible Light Communication system called VIDAS for transmitting traffic information to vehicles. VIDAS uses LED traffic lights to transmit data to onboard vehicle receivers via visible light modulation. Key components discussed include the multiple LED emitter source, PIN photodiode detector, front-end amplifier, direct sequence spread spectrum modulation, and considerations for noise and signal variation over distance. Experimental results showed VIDAS enabled reception of traffic information from 100m away and adaptation to changing signal strength as vehicles approached intersections.

1. CONTENTS
Introduction.
 Overview of Visible Light Communication.
 General system architecture.
 VIDAS In Intelligent Transportation Systems (ITS).
 Conceptual Design of VIDAS.
 Multiple LED Emitter Source.
 The Detector and Front End Amplifier.
 Modulation and Demodulation in VIDAS.
 Traffic System set- up for VIDAS.
 Experiment setup and important results.
 Conclusion.

2. INTRODUCTION:
 Visible Light Communication (VLC) using LEDs is
emerging as a key technology for a ubiquitous
communication system.
 This presentation addresses the utilization of VLC in
wireless Advanced Driver Assistance System (ADAS)
which can be referred to as VIDAS.
 The VIDAS is an advanced outdoor application of
VLC to reduce road accident and fatality by
transmitting traffic information in advance to running
vehicles.

3. VISIBLE LIGHT COMMUNICATION
VLC is an emerging and novel Optical Wireless
communication system which uses visible spectrum
(approx. 380nm-750nm) emitted from light emitting diodes
(LEDs).
VLC is becoming an alternative choice for next-
generation wireless access technology by offering
Vast and Unregulated Bandwidth.
Efficiency
Security
Use of LED‟s

4. Comparisons
between Visible
light spectrum with
other spectrums.

5. Why use LED’S?
 High efficiency (70-80%
of energy saving),
 Low maintenance cost.
Long life (>100,000 hrs).
Illumination in desired
direction.
HIGH RATE SWITCHING CAPABILITIES.

6. GENERAL SYSTEM ARCHITECTURE

7. VIDAS In Intelligent Transportation Systems (ITS)
The term intelligent transportation systems (ITS) refers to
information and communication technology (applied to
transport infrastructure and vehicles) that improve
transport outcomes such as transport safety, transport
productivity, travel reliability etc.
The VIDAS in ITS involves transmitting road safety
traffic information to assist drivers while driving on road.
The VIDAS concept can be extended in car-to-car
communication.

9. CONCEPTUAL DESIGN

10. Multiple LED Emitter
Source

11. Typically LEDs with half power angle (hpa) of 15deg to 45deg are
used.
The emitter is modeled using a generalized Lambertian radiation
pattern (Re(φ,m))
Assuming that Pt is the transmitted power, the radiation intensity
is given by:
Radiation pattern as a function of „m‟ and „φ‟

12. The Detector and Front End Amplifier
 At the receiver a PIN photodiode converts the optical signal
into an electrical current, which is further amplified by a front-
end amplifier.
 The Detector achieves an effective signal-collection area of
Where Ad is the detector physical area and σ is the angle
of incidence with respect to the receiver axis.
Receiver Field of View
Cone(FOV).

13. Front End Amplifier
 In order to meet the requirements of high sensitivity, gain
and higher dynamic range, transimpedance amplifiers (TIA)
with switched feedback network scheme as shown in fig a is
used.
 In the design considerations of front-end the trade off
between gain and dynamic range plays an important role.

14. Modulation and Demodulation
 Unlike other conventional communication systems,
VLC will need a robust Modulation and Demodulation
scheme.
 Mainly because of many sources of interference (noise)
such as ambient, fluorescent light, day light, lights from
other vehicles and so on.
 In addition, different atmospheric conditions will have
significant effect on the VLC performance.
 Direct Sequence Spread Spectrum (DSSS) Sequence
Inverse Keying (SIK) modulation technique which is
found to be very effective against such interference.

15. Direct Sequence Spread Spectrum
Sequence Inverse Keying for VIDAS

16. NOISE SOURCES
Noise sources are an important challenge to overcome
towards the feasibility of VLC systems. These are: thermal
noise; shot noise; and optical excess noise.
Thermal noise is associated with the photodiode‟s resistors,
and is considered a white noise source with small spectral
density.
Natural and artificial light sources create a steady background
irradiance which causes shot noise and optical excess noise.
These noises can be reduced by controlling the amount of
background radiation collected. Using a narrower FOV and an
optical IR cut-off filter is a desirable solution.

17. Traffic System set- up for VIDAS
Simple(one lane) traffic system set up
for VIDAS(LOS propagation model)

18. Important design parameters

19. EXPERIMENT SETUP
Considering the LOS propagation model and parameters
involved and using the conceptual design, a prototype of
VIDAS for traffic information transmission using traffic
lights was constructed.
The developers of VIDAS then conducted experiments by
varying certain parameters.
Following are the initial conditions considered.
Average speed of vehicle – v=50Km/h
Packet size - 100Kb
Service Area Umin to Umax - 100m
Transmission rate - Rb = 1Mbps
Packet service area - 1.39m

20. IMPORTANT RESULTS
 The vehicle starts receiving information from a distance
of 100m from the traffic point in the first lane.
 As the vehicle approaches towards traffic light the
power variation is considerable and the receiver must be
able to adapt such variation to give necessary output.
 Based on this information, it is possible to design a
receiver either for varying packet size over a distance unit
or adjusting the gain keeping fixed packet size.

21. Gain variation over the distance for
different values of h and optimized Ѳ

22. The graph shows variation of % message
received vs. distance x(m) for three situation i.e.
in dark environment, in daylight and at night
with street lights on.

23. CONCLUSION
 Omni Present, Unlicensed and Unregulated Visible Spectrum
based technology can very well supplement congested radio
frequency based systems.
 As the VLC applications in outdoor especially in ITS is at very
early stage, experimental results from prototype VLC guarantees
data communication from infrastructure-to-vehicle, broadcasting
many safety related information, hence suitable for road safety
applications.
 Although some of the design challenges have been simplified
in this paper, a number of complex issues remain. more research
is needed to explore bi-directional link, high data rate
transmission etc.

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