Li-Fi is a label for wireless-
communication systems using
light as a carrier instead of
traditional radio frequencies,
as in Wi-Fi .
Li-Fi should not be confused
with the more general term
visible light communications
(VLC), which is the use of the
visible light portion of the
electromagnetic spectrum to
transmit information. The
term Li-Fi was coined by
Professor Harald Haas from
the University of Edinburgh in
the UK and pureVLC’s CSO,
and refers to a type of VLC
technology that delivers a
networked, mobile, high-
speed communication
solution in a similar manner
as Wi-Fi. Therefore, the
fundamental pre-requisite for
Li-Fi is a bi-directional link
over the same medium. The
term was first used in this
context by Harald Haas in
his 2011 TED Global talk on
visible light communication.
In October 2011, a number of
companies and industry
groups formed the Li-Fi
Consortium, to promote high-
speed optical wireless
systems and to overcome the
limited amount of radio-
based wireless spectrum
available by exploiting a
completely different part of
the electromagnetic
spectrum. The consortium
believes it is possible to
achieve more than 10 Gbit/s ,
theoretically allowing a high-
definition film to be
downloaded in 30 seconds.
In fact, Dr Gordon Povey
provides a top level overview
of VLC development until the
end of 2011. A number of
companies offer uni-
directional VLC products,
however, the only known bi-
directional system on offer is
by pureVLC. PureVLC is an
original equipment
manufacturer (OEM) firm set
up to commercialize Li-Fi, by
bring out Li-Fi products for
integration with existing LED -
lighting systems.
VLC technology has been
exhibited on numerous
occasions and has chiefly
developed over the last
decade with the specific
drive by Prof. Harald Haas
focusing on Li-Fi, rather than
just VLC. Indeed, pureVLC
demonstrated the world's
first streaming Li-Fi system
to complement VLC data
rates of over 6 Gbps .
Furthermore, pureVLC was
also the first to prove that
that Li-Fi, or VLC systems in
general, do not require line-
of-sight conditions.
Li-Fi has the advantage of
being able to be used in
electromagnetic sensitive
areas such as in aircraft,
nuclear power plants, oil &gas
installations and other
places without causing
interference. However, the
light waves used cannot
penetrate walls which makes
Li-Fi significantly more secure
relative to Wi-Fi.
Standardization
VLC communication is
modeled after communication
protocols established by the
IEEE 802 workgroup. This
standard defines the physical
layer (PHY) and media access
control (MAC) layer. The
standard is able to deliver
enough data rates to
transmit audio, video and
multimedia services. It takes
count of the optical
transmission mobility, its
compatibility with artificial
lighting present in
infrastructures, the defiance
which may be caused by
interference generated by the
ambient lighting. The MAC
layer allows to use the link
with the other layers like the
TCP/IP
protocol. [citation needed]
The standard defines three
PHY layers with different
rates:
The PHY I was established
for outdoor application and
works from 11.67 kbit/s to
267.6 kbit/s.
The PHY II layer allows to
reach data rates from 1.25
Mbit/s to 96 Mbit/s.
The PHY III is used for many
emissions sources with a
particular modulation method
called color shift keying
(CSK). PHY III can deliver
rates from 12 Mbit/s to 96
Mbit/s. [10]
The modulations formats
preconized for PHY I and PHY
II are the coding on-off
keying (OOK) and variable
pulse position modulation
(VPPM). The Manchester
coding used for the PHY I
and PHY II layers include the
clock inside the transmitted
data by representing a logic
0 with an OOK symbol "01"
and a logic 1 with an OOK
symbol "10", all with a DC
component. This is an
important point because the
DC component allows to
avoid the light extinction in
case of an extended line of
logic 0. [citation needed]
The Li-Fi Consortium has also
been established to work on
standardizing VLC
communications, but the
rapid evolution of the
technology minimizes the
impact of any
standardization effort. Both
the IEEE 802 workgroup and
the Li-Fi Consortium fail to
account for the emergence of
optical orthogonal
frequency-division
multiplexing (O- OFDM )
systems which provide
significant benefits with
regard to data rates,
multiple-access and energy
efficiency.
