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978-1-5090-1081-3/17/$31.00 ©2017 IEEE
2017 International Siberian Conference on Control and Communications (SIBCON)
LED-Based Visible Light Communication and
Positioning Technology and SoCs Tian Lang, Zening Li, Gang Chen and Albert Wang ([email protected])
Center for Ubiquitous Communications by Light, University of California, Riverside, CA 92521, USA
Abstract— The rapid deployment of high-energy-efficiency,
solid-state light emission diode (LED) lighting devices, replacing
the conventional luminaires devices, brings unprecedented
opportunities for alternative optical wireless communication and
navigation applications. This paper reviews the state-of-the-art of
LED-based visible light communications (VLC) and positioning
(VLP) technologies with a focus on system-on-a-chip (SoC)
integrated circuit (IC) designs.
Index Terms—Visible light communication, VLC, visible light
positioning, VLP, LED, optical wireless, rolling shutter, system-
on-a-chip, SoC, IC.
I. LED ILLUMINATION
With recent revolution on illumination technology, the
widely used incandescent and compact florescent light (CFL)
bulbs are being quickly replaced by solid-state Light Emitting
Diode (LED) devices. LED is a green lighting technology
featuring high energy efficiency of 120 lumens per watt today
and possibly 200 lumens per watt by 2020, compared clearly
more favorable than incandescent bulbs (~15 lumens per watt)
and CFLs (~73 lumens per watt) [1]. LED bulbs also have
much longer lifespan, at least 3 fold longer than traditional
bulbs. LED’s other advantages include compact form factor,
being “cold” and higher color rendering, making LEDs the
clear choice as the next-generation illuminating devices.
Solid-state LEDs can be switched ON/OFF at tens of MHz
without flickering to human eyes, which is equivalent to
modulation in communications. Therefore, LEDs can be used
to realize visible light communications, which makes the
dream of communicate as you see become a reality. The
revolutionary LED-based VLC technology has many
advantages over traditional RF-based wireless technologies [2-
5]: First, the unlicensed and unrestricted optical spectrum
offers a bandwidth up to 300THz, orders of magnitude wider
than the RF spectrum, hence, making wireless streaming at
multi-Gbps possible. Second, the radiation of visible light is
largely harmless and hence allows more emission power to
boost data rates and distance. Third, unable to penetrate walls,
VLC has higher security by nature. Fourth, being interference-
free, VLC technology can co-exist with and complement
existing RF technologies. Fifth, LEDs are much cheaper than
multi-GHz RF devices. Importantly, VLC communication can
take full use of the existing LED light infrastructure around the
world to realize “free” wireless applications. In addition to
VLC, LED enables visible light positioning, which addresses
many limiting factors inherent to RF-based navigation
technologies, such as the popular global positioning system
(GPS). LED-based VLP technology hence opens a door for
unlimited indoor and outdoor ranging and navigation
applications, such as smart traffics and smart hospitals [6-12].
II. VLC SYSTEM IN SOC
The interests in VLC technology have grown rapidly ever
since researchers from Keio University published their result
on a white LED in home network access method [13]. The
waves of VLC research led to the formation of Visible Light
Communication Consortium (VLCC) in Japan in 2003 [14] and
spreads globally [6-12]. Two standards, Visible Light
Communication System Standard and Visible Light ID System
Standard were proposed by VLCC in 2007. In Europe, hOME
Gigabit Access project (OMEGA) [15], sponsored by
European Union, has shown VLC as an alternative way to
support RF communication network in 2009. IEEE Standard
802.15.7 was established for VLC communications in 2011
[16], which standardizes VLC’s the links and physical layer
design specifications for system designs.
A. VLC Architecture
A VLC system has two main parts, a transmitter and a
receiver. Fig. 1 illustrates a typical VLC system diagram. A
simple transmitter consists of an LED luminaire, a driver
circuit and a modulation circuit, which modulates the data onto
the fast intensity switching light emitted from the LED. For the
LED luminaire, there are two methods to produce a white light,
blue LED with phosphor or Red-Green-Blue (RGB) LEDs
combination. The former method utilizes the blue light and the
yellow phosphor combination to produce a white light, which
is the most common method due to its simplicity and low cost.
The latter method utilizes the mixing of red, green and blue
lights to render a white, which is not as cost effective. The
driver and modulation circuit modulates the input electrical
signal and convert it into optical output signal. One of the VLC
design constraints is not to affect the primary function of the
LED bulb as an illumination device, as such, the performance
of VLC functions will be affected in general.
The receiver of a VLC system contains the optical receiver
and a demodulation circuit. There are two types of optical
receiver, photodetector (PD) and imaging sensor. PD devices
are commonly used in VLC systems. The current generated
depends on the received light intensity. Due to the lack of
phase information in the received visible light signal, intensity
modulation/direct detection (IMDD) scheme is typically used.
The imaging sensor is also called a camera sensor (CMOS or
CCD). It is available in almost mobile devices today, which has
the potential to make the VLC implementation as easy as
simply installing a VLC App without any optical receiver add-
2017 International Siberian Conference on Control and Communications (SIBCON)
on, provided the LED-based illumination infrastructure has
already enabled VLC modulation.
Fig. 1. A simplified block diagram of a conceptual VLC system.
B. VLC SoC Designs
Global research efforts on the VLC technology has resulted
in many demonstration of VLC testbed systems of varying
wireless streaming performance. So far, reported VLC systems
are bulky because of using commercial off-the-shelf (COST)
devices [2-8]. Unfortunately, while such COST-based VLC
testbeds are good for quick feasibility studies, they are
impractical for real-world applications and also have
fundamental limitation on VLC performance. It is apparent that
in order for LED-based VLC applications become a true reality,
IC-based system-on-a-chip (SoC) and/or system-in-a-package
(SiP) design is a must, which is an emerging challenge in VLC
system research. In [12], Dong reported the first single-chip
custom-designed VLC transceiver IC that successfully driven
an LED-based VLC system to stream data. This single-chip
VLC IC consists of opto-electrical signal conversion, filtering,
bandwidth enhancement, low-noise pre-amplification, power
amplification, and analog-to-digital conversion and digital
signal processing (DSP) functions.
1) Discrete Transceiver Design for VLC System
Fig. 2 depicts a typical VLC system allowing both host-
slave broadcasting (LED bulb to users) and peer-to-peer full-
duplex transceiving (user to user). The transmitting path
includes buffers, coding and OFDM modulation for better
signal quality, a pre-equalizer for wider bandwidth, driver and
DC biasing for large LED array, DEMUX to handle LED array
signals, and digital-to-analog convertor (DAC) and global
clock synchronization. The receiving channel consists of pre-
amplifier and main amplifier, high/low pass filters, ADC to
convert the received analog signals into digital, decoding and
demodulation to recover signal information, a post-equalizer to
enlarge receiver bandwidth, clock synchronization and CDR
(clock and data recovery) circuit to recover both clock and data
from incoming signals. Two types of photo sensors may be
used: a large PD array and a CMOS imager. A MUX circuit is
used for PD array to fuse the received parallel signals. MAC
blocks will be used for access control for multi-users. LVDS
can be used to remove background noises. On-chip ESD
protection is needed for real-world VLC products.
2) VLC Transceiver IC Design
[12] reports a SoC IC for the VLC transceiver as illustrated
in Fig. 3, which was designed and fabricated in a foundry
180nm BCDMOS technology. The VLC transceiver IC
consists of a LED luminaire transmitter, equalization control
unit, Manchester encoding and decoding block, phase lock
loop (PLL), voltage and current reference, and optical receiver.
It was designed to realize up to 64bit digital control for test
multiplexer control by the I2C protocol, I2C slave and 8 digital
registers. There are a total of 25 IO pads, which includes two
for testing mux outputs and two for I2C programming
interfaces. The IC die is 2mmX2mm and uses BGA bonding.
S2D
LED Driver
PLL
Manchester
Clock & Data
Recovery Recovered Clock
Manchester
Encoding
Comparator
LED Driver
Interface
Equalization
Control
Recovered Data
Data
Clock
Voltage &
Current
Reference
LA TIA
PLL_outI
2C Interface
Digital Logic
And Control
SCL
SDA
TIA
_ou
tp
TIA
_o
utn
Co
mp
_o
ut
DSP
Photodiode
LED
sw
VLC Transceiver
Fig.3. Illustration of the fully integrated transceiver SoC IC for LED-based
VLC system in 180nm BCDMOS [12].
Fig. 4 depicts the hierarchy of the VLC transceiver SoC IC.
The VLC transceiver can be categorized in 3 main functional
parts: IO pad-ring, Analog and Digital portions. The Analog
portion includes 4 blocks, which are transmitter, PLL, bandgap
and receiver. The transmitter block has Manchester encoder,
delay cells, equalizer and LED Driver. The receiver comprises
4 blocks, which are front-end, linear amplifiers, comparator
and Manchester decoder. The Digital portion includes I2C
slaves, I2C registers, signal start and stop detection, and a
counter. The IO Pad-ring portion has power on reset (POR)
designed to set the initial value of all of the digital logics and
power supply detection. The communication between I2C
master and slave is ensured by I2C buffer via I2C bus lines.
On-chip electrostatic discharge (ESD) protection is designed
for each IO pad. This VLC transceiver IC allows simultaneous
illumination and communication by LED. On the transmitter
side, pre-equalization and multi-stage amplifier enhance the
modulation bandwidth limited by the LEDs. The signal
waveform received through the visible light transmitted from
the LED luminaire is 12 MHz. On the receiver side, VLC-
specific TIA and comparator were designed. This VLC
transceiver SoC operates over a bandwidth of 50 MHz.
Fig. 2 Illustration of a LED/imager based full duplex VLC wireless system.
US
B Biasing
ClockSignal
1:N
DE
MU
X
TX
MACBuffer Coding DAC
OFDM
ModulationDriver
Pre-
Equalizer
M:1
MU
X
Pre-AmpAmp
Filter
DeMod De-Coding ADCRX
MAC
Post-
Equalizer
CDR LEDArray
PINArray
1:N
DE
MU
X
TX
MACBufferCodingDAC
OFDM
ModulationDriver
Pre-
Equalizer
Pre-Amp Amp
US
B
CDR
Filter
DeModDe-CodingADCRX
MAC
Biasing
Post-
Equalizer
Clock
Signal
LEDArray
2017 International Siberian Conference on Control and Communications (SIBCON)
Digital_TopAnalog_TopIO Padring
VLC_Transceiver
POR
ESD Padring
I2C Buffer
Test Mux Buffer
I2C Slave
I2C Register
Start_stop_det
Counters, etc.
Transmitter PLL Bandgap Receiver
Machester Encoder
Equalizer
Front-end
Linear Amplifiers
LED Driver
Comparator
VCO
PFD/CP
Divider
FilterManchester
Decoder
Power Domain
Delay Cells
Fig.4. Hierarchy of the VLC transceiver SoC in 180nm BCDMOS [12].
III. VISIBLE LIGHT POSITIONING SYSTEM
RF-based positioning technology has its limitation. For
example, GPS does not work indoor. RF wireless technologies
may be prohibited in certain environments, such as hospitals.
LED-based VLP technology may have many indoor/outdoor
ranging and navigation applications in addition to VLC
functions, for example, for smart traffics and smart hospitals.
A. VLP System
The positioning functionality of LED-based VLC is rapidly
developed with its unique advantages over its RF counterparts,
such as cellular, WiFi, Bluetooth and RFID. One advantage is
the utilization of visible light’s line of sight (LOS) property,
which enables the PD receiver to detect the rotation and
location of the target based on the information from a set of
reference LEDs. This advantage reduces the uncertainty caused
by hardware and antenna orientation. Another benefit from the
LOS property is that the multi-path effect can be ignored due to
its IMDD method compared to RF positioning techniques. The
deployment of VLP systems utilizing the LED illumination
infrastructure lays the ground for many positioning
applications, for example, asset and personnel tracking.
B. VLP Tracking Methods
Various tracking techniques using LED-based VLP
technology were developed. Fig. 5 shows a simple Proximity
method in which the grids are separated due to the difference
of three different signals. The simplicity of this method comes
with its limitation, i.e., the tracking precision depends heavily
on the grid density of its reference points [17]. This VLP
positioning technique is useful for smart hospitals to realize
asset and personnel tracking in real time.
Another technique is the scene analysis technique that
functions in two phases [18]. In phase one, it collects needed
finger prints such as on received signal strength (RSS), time of
arrival (TOA) and time difference of arrival (TDOA). In phase
two, the routine matches the real time data with those collected
fingerprints in phase one. This method is simple for signal
processing that requires matching only. However, fingerprint
collection sets the limit for many tracking applications. [19]
presents a triangulation method based on RSS, which utilizes
the method of angulation and multilateration. By using
multilateration, the position of the target is measured indirectly
from references such as TOA, RSS and TDOA. By using
angulation, the target location can be estimated by its relative
angle with respect to the reference.
Fig.5. A simple proximity method for VLP smart tracking [17].
C. Rolling Shutter Enabled Multi-View Geometry Positioning
Fig. 6 shows a new rolling shutter enabled positioning
method for a LED VLP tracking system for smart hospitals
[17]. The LED luminaires are individually modulated with a
unique frequency as their optical tags. Optical beacon can be
broadcasted via each LED operating at a unique frequency, so
that the smartphone camera can retrieve it from a reflected
surface by analyzing rolling shutter effect. It can also acquire
the beacon information from LED directly. The rolling shutter
effect works with the dark and white bands seen by the
smartphone camera from the modulated LED lights. The image
is processed to extract the frequency component corresponding
to different LEDs. These striped images will be processed to
retrieve different frequency illuminated by these LEDs. The
actual position of an object can be calculated by these acquired
frequency information and compared with a pre-installed map
of the setting, therefore, realizes asset/personnel tracking in
real time. This new LED-based VLP smart tracking method
utilizes both the multi-camera vision triangulation algorithm
and rolling shutter effect, and the multi-view geometry. The
design focus is to determine the offset between two camera
frames in order to derive the target position. Both
accelerometer and gyroscope sensors can be utilized to monitor
the pose changes between two frames. The relative position
and pose of the device are tracked over the entire positioning
process. Based on the relative position and pose of the previous
frames, the current camera frames are estimated in the global
frame. The estimation inaccuracy due to shot noises from the
sensors, approximation error, or temporary blocking of the
LED light can be resolved by using two-stage Kalman filter
[20]. Therefore, the new LED VLP smart tracking system is
able to utilize only one detected LED with known position and
built-in smartphone sensors, such as motion, position and
2017 International Siberian Conference on Control and Communications (SIBCON)
environment sensor, to track actual position even when the
optical link is temporarily blocked or the LED moves out of the
FOV of the camera momentarily [17].
Fig.6. Illustration of the new LED VLC smart tracking system [17].
IV. VLC AND VLP APPLICATIONS
The LED-based VLC and VLP technology is an alternative
solution for RF wireless communications and positioning. The
followings are a few application examples demonstrated [14].
1) Indoor Wireless Networking: The existing indoor LED
light infrastructures can be retrofitted to realize full duplex
wireless streaming. Due to the extremely wide bandwidth of
visible light, VLC communication can be a viable wireless
solution for big data communications. Fig. 7 shows a full
duplex LED VLC testbed at the UC-Light Center of University
of California [21], capable of streaming HD videos while
allowing wireless communications between the two terminals.
Fig. 8 shows a VLC system using the VLC transceiver SoC
designed in 180 BCDMOS technology for visible light
streaming [17].
2) Outdoor VLC Networking: Urban development can use
outdoor LED-based VLC systems to realize smart city
applications. For example, the LED display boards, street lights
and LED signs can be redesigned to form a grand wireless
network for a city, a community, airport buildings, sports
arenas, large parking structures and shopping centers,
essentially making the smart city concept a reality.
3) Smart Hospitals: Modern hospitals requires high-volume
information communications (e.g., for telemedicine) and real-
time asset and personnel management. RF wireless is not the
solution due to many limitations. Build the VLC/VLP
functions into the existing LED light infrastructure will achieve
high-throughput wireless streaming and accurate
asset/personnel tracking, hence, making smart hospital a reality.
Fig. 9 shows a demo of a VLC system at the Loma Linda
Medical Center designed by the UC-Light Center [14].
4) Smart Traffics:
Adding the VLC/VLP functions to street lights, street signs,
LED displays, and the head/tail lights of vehicles, will make a
huge real-time traffic data monitoring and collection network,
which can be used to realize truly smart traffic control
everywhere and anytime. Fig. 10 shows a demo VLP/VLC
vehicle at the UC-Light Center that features VLP navigation
and VLC wireless communications simultaneously.
V. SUMMARY
We review the basics and state-of-the-art of the new LED-
based VLC and VLP technologies and systems. Designs of
VLC/VLP SoCs are discussed for real-world applications. The
VLC/VLP technology opens a door to unlimited wireless
applications, including high-throughput wireless streaming for
big data applications, smart cities, smart hospitals and real-time
smart traffic control.
ACKNOWLEDGMENT
This work was partially supported by the MRPI Program of
California, National Science Foundation and the Department of
Defense of the USA.
Fig. 7 A dual-user LED VLC system for HD video streaming [14].
Fig. 8 A demo at the UC-Light Center uses the VLC SoC IC designed in an 180nm BCDMOS to realize visible light communication [14].
2017 International Siberian Conference on Control and Communications (SIBCON)
Fig. 9 Demo of a VLC system at the Loma Linda Medical Center [14].
Fig. 10 A demo vehicle with VLP navigation and VLC communications [14].
REFERENCES
[1] United States Department of Energy, “The History of the Light
Bulb,” https://energy.gov/articles/history-light-bulb, 2013.
[2] J. P. Conti, “What you see is what you send”, Engineering &
Technology, pp. 66-68, November 2008.
[3] M. Kavehrad, “Broadband room service by light,” Scientific
American Magazine, pp. 82-87, July 2007.
[4] M. Kavehrad, “Sustainable energy-efficient wireless
applications using light”, IEEE Communications Magazine, pp.
66-73, Dec. 2010.
[5] H. Minh, Z. Ghassemlooy, D. O’Brien and G. Faulkner, “Indoor
gigabit optical wireless communications: challenges and
possibilities”, Proc. IEEE ICTON, pp. 1-6, 2010.
[6] Y. S. Hussein, M. Y. Alias and A. A. Abdulkafi, "An
Implementation of Indoor Visible Light Communication System
Using Simulink," Proc. Int’l Conf. Platform Technology and
Service, 2017.
[7] A. A. Abdulkafi, M. Y. Alias and Y. S. Hussein, "A Novel
Approach for PAPR Reduction in OFDM-Based Visible Light
Communications," Proc. Int’l Conf. Platform Technology and
Service, 2017.
[8] H. Han, M. Zhang, P. Luo, W. Xu, D. Han and M. Wu, "Real-
time bi-directional visible light communication system," Proc.
ICOCN, 2016.
[9] T. Lang, Z. Li, A. Wang and G. Chen, “Hemispherical Lens
Featured Beehive Structure Receiver on Vehicular Massive
MIMO Visible Light Communication System”, Proc. Int’l Conf.
Internet of Vehicles, pp.469-477, 2015.
[10] T. Lang, Z. Li, A. Wang and G. Chen, “Hemispherical Lens
Featured Beehive Structure Receiver on Vehicular Massive
MIMO Visible Light Communication System”, Internet of
Vehicles - Safe and Intelligent Mobility, Vol. 9502, Print ISBN:
978-3-319-27292-4, Springer International Publishing, pp.469-
477, November 2015.
[11] Z. Li, L. Liao, A. Wang and G. Chen, “Vehicular Optical
Ranging and Communication System”, EURASIP J. Wireless
Communications and Networking, 2015:190;
doi:10.1186/s13638-015-0415-1, 2015.
[12] Z. Dong, F. Lu, R. Ma, L. Wang, C. Zhang, G. Chen, A. Wang
and B. Zhao, “An Integrated Transmitter for LED-Based Visible
Light Communication and Positioning System in A 180nm BCD
Technology”, Proc. IEEE BCTM, pp. 84-87, 2014.
[13] Y. Tanaka, et al., “Indoor visible communication utilizing plural
white LEDs as lighting,” Proc. IEEE PIMRC, pp. F81–F85,
2001.
[14] Visible Light Communications Consortium (VLCC),
http://www.vlcc.net/
[15] Home Gigabit Access (OMEGA) Project, http://www.ict-
omega.eu/
[16] IEEE Standard for Local and Metropolitan Area Networks-Part
15.7: Short-Range Wireless Optical Communication Using
Visible Light, IEEE Std. 802.15.7, Sep.2011.
[17] Li, Zening, Indoor Positioning System Using Visible Light
Communication and Smartphone with Rolling Shutter Camera,
PhD Dissertation, University of California, Riverside, 2016.
[18] A. Papapostolou and C. Hakima, "Scene analysis indoor
positioning enhancements," annals of telecommunications-
annales des télécommunications, 66.9-10 (2011): 519-533.
[19] T. Komine and N. Masao, "Fundamental analysis for visible-
light communication system using LED lights," IEEE Trans.
Consumer Electronics, 50.1 (2004): 100-107.
[20] G. Welch and G. Bishop. "An introduction to the Kalman filter,”
University of North Carolina at Chapel Hill, 2006.
[21] Center for Ubiquitous Communication by Light (UC-Light),
University of California, http://www.uclight.ucr.edu.