Visible Light Communication and Augmented [631719]

Visible Light Communication and Augmented
Reality for Underground Positioning System
Simona Riurean*, Marius Olar1, Andreea Ionică2, Lilla Pellegrini1
1University of Petro șani, Department of Computer and Electrical Engineering, Universit ății str., no.
20, 332006 Petro șani, România
2University of Petro șani, Department of Management and Industrial Engineering, Universită ții str.,
no. 20, 332006 Petro șani, România
Abstract. Visible Light Communication (VLC) technology allows
wireless data transmission piggybac ked by illumination. Highly accurate
and reliable system s based on VLC, as Indoor Positioning System (IPS)
have been already developed by academics and specialized companies .
Underground Positioning System (UPS) addressed here is embedded into
the protecti on equipment , compulsory to be used underground, being
therefore importan t to workers in potential dangerous spaces since fast data
communication and real -time data interpretation is therefore possible . This
paper presents the VLC technology implemented in mining underground
specific environment for an accurate positioning and fast data
communication for underground navigation with the main aim of
developing a real time warning and alarming system based on Augmented
Reality (AR) and Neural Networks (NN s) principles .
1 Introduction
The VLC has been for the first time proved in the Japan’s M. Nakagawa Laboratories in
2003 [1] and, as a result of their research, a VLC ID System Development Kit was
available on 2012 [2]. Significant other quick implementation of VLC as an IPS has been
done in France by Oledcomm Company in museums and offices in 2012 as well as in Lille
Carrefour supermarket on 2015 [3]. Acuity Brands demonstrated on 2014 both at Lightfair
and Lux Live in London ByteLight IPS using LED lighting based on intelligent drivers
from eldoLED. Qualcomm company from USA presented in 2016 its own IPS project
based on VLC Lumicast. Using Lumicast VLC, a smartphone (SP) was capable to
determine its position relative to LED ambient light fixtures within 10 c m radius, and
deliver an accurate orientation of the direction the user was facing . Qualcomm and Acuity
Brands collaborate to commercially deploy IPS project in more than 100 USA retail
locations. Recently, the adoption of VLC technology assis ts retailers to augment customer
experience by bringing digital channels to physical stores, such as enabling location -based
interaction on mobile devices, which can drive in -store sales.

* Corresponding au thor: [anonimizat]

In industrial practice, t he augmented reality (AR) was introduced in 1990 when To m
Caudell implemented a computerized system in Boeing's factories, displaying virtual
graphic elements over certain objects, facilitating the design of electrical wiring. [5].
Neural networks (NNs), as adaptive instruments for parallel processing , aim to resolve
computational issues. The origin of the NN derive s from biological structures , being useful
to develop NNs that can be used to develop systems based on VCL and AR. NNs are
suitable for solving tasks that barely can be solved by the conventional alg orithmic
approach, t or with classic methods of artificial intelligence (e .g. rule-based systems).
2 Technologies used for the system described
2.1 Visible Light Communication Technology
VLC as an optical wireless technology , uses visible light pulses emi tted by Light Emitted
Device s (LEDs ) to transmit binary data. It is efficient in terms of the speed of data transfers
and security, while also providing accurate transmission. It is one of the most recent
developments of IPS.
Smart LED technology is known for generating important energy savings and overall
improvement in lighting quality. Because LED lighting can be rapidly modulated or fast
turned on and off, adding an intelligent driver, able to power LEDs in a manner that
produces Morse code -like light patterns at a very high rate that can be perceived by human
eye as a continuous light. Intelligently driven LED lights, relay on image sensors to provide
a highly effective method to enable location and navigation within indoor environments.
2.2. Augmented Reality Technology
AR technology extends human sensory capacity by accessing additional environmental
information, either in the form of images, sounds or text. This information is superimposed
on the information received naturally, biologically, so virtu al elements will be projected
over the elements of the environment, and with the perception of space, 3D will be
designed among the elements of the environment. With d igital enhanced r eality , objects are
created by the computer, but they generate data acqu ired by sensors (audio -video,
recognizable objects, GPS location, etc.). In contrast, Virtual reality replaces Real reality
with a simu lated one [6].
2.3. Neuronal Networks as Predictive Tool
Scientists have been always interested in predicting an event based on a sequence of
previously occurred events. Event sequence prediction has numerous applications, as the
ability to predict the next word in language modelling or a new app launching, given the
usage history. Event sequence prediction often decompose s into two classes: discrete -time
event sequence prediction and continuous -time events sequence prediction. The first class
offers a sequence that include a series of activities where every event may be listed by
using its order position in the sequence, w hich evolves synchronously in natural unit -time
steps. These sequences are integrally time -independent. Continuous -time event sequence
prediction mostly appears to the sequences where the events happen asynchronously. For
example, the duration between cons ecutive log-in events into an online service can change
from time to time. Therefore, one primary goal of continuous -time event sequence
prediction is to predict when the next event will happen in the near future [ 7].

The NN can be trained to do prediction . There are some time series, i.e., a variable x
varying in time x t (t=1,2,…) and the question is what value will have x in t+h moment. The
estimation of time series with NNs involves training the NN the history of the variable in a
particular time and a pplying the taught information to the forthcoming events. Previous
data are providing the inputs of NN and it is expected that the output data will predict what
is going to happen in the future. The learning method is the supervised learning. For a more
accurate prediction, supplementary information can be added for teaching and prediction,
for example in the form of interventional variables. Nevertheless, more information does
not always mean better prediction; occasionally it can slow down the pro cess of teaching
and predicting. It is always essential to choose truly pertinent information, if there is any.
Various types of NNs can be used for prediction, such as backpropagation, recurrent neural
networks, Marks network and so on [8].
3. UPS for Environmen ts with High Explosion Hazard
The Underground Positioning System (UPS) addressed here consists of a very useful too l
both for a better orientation, a real – time notification o f the end –users as well as prediction
of certain situations or events. VLC tech nology is especially suitable in environments
where radio frequencies’ use is limited or forbidden. In explosive underground
environments the VLC technology uses the existing LED light fixtures as transmitter (oTx)
element and the Front Sight (FS) of a Sma rt Helmet (SH) as both VLC receiver (oRx) and
AR device for location transmitters and navigation information display.
The FS of a VLC receiver embedded SH allow fast data wireless communication since
they sense the overhead LED lighting beacon, transformi ng it into an underground location
waypoint. These LED based waypoints allow end -users both to find their precise
underground location assisting them in navigation to other specific locations and to be
aware in real time of the important environmental para meters in underground hazard
locations. The positioning signals are decoded by the SH with both the FS and oRx VLC .
The pinpoint accuracy it delivers is vital since can only locate the SH user within
several meters [ 9]. The fast communic ation speed allows a person localization within 1/10
of a second. Orientation is also provided by displaying direction where the worker is facin g.
Hybrid IPS based on VLC and AR is clearly the best performing technology to enable
underground location services. LED light fixt ures spread positioning signals using rapid
modulation of light in a way that does not disturb their main functionality of illumination.
When the end -user passes through a special zone, the FS displays its position as well as
useful information of that spe cific zone or “micro -fence.” At that phase, FS display gives
the opportunity to directly engage the end -user with an alert, a notification regarding a real
time event such as high methane level alert, dropping the ceiling or accidents, a message
designed t o create safety notification with great value for the end -user. Thus, proximity
notification is considered to be a significant means of increasing safety in underground
areas. Further than proximity solutions, underground positioning solutions can be more
refined, delivering better accuracy with real -time attributes. Positioning can display the
user’s location on a floorplan, just like a moving blue dot on a map. This level of detail can
enable “you are here” applications, wayfinding, turn -by-turn solutions and more.
The oRx LED and FS are both embedded in SM being supplied by the same battery of
the miner’s lamp. The FS’ transparency allow end -user to view at the same time, both the
environment and data displayed.
Each LED fixture transmits its N -S and E -W coordinates, as well as the depth measure
related to the zero point located at the mine surface. While collecting all these data, a 3D
spatial mine representation is created, mapping the mine’s underground spaces where the

end-users are localized. The gra phical representation of the miners’ location is done in any
graphic interface for GPS location, by the symbol of a pointer
or a circle
.

Fig. 1. UPS– LED as oTx and SH with the FS and VLC oRx technology embedded

The gas sensors detect and transmit th e gas level results to the surface control centre
every 2 seconds. The values stored in a database will be transmitted, via existing
illumination network to the specific local VLC LED lighting fixture, to the FS to display
them. The FS display will show in real-time the information received with the evolution of
gas concentrations and/or temperature level. These information, the end -user location and
gas concentration values, are very important data especially during rescue missions of
injured persons or ju st for regular work environmental monitoring. The display will show
additional information regarding closed routes, location of first aid points or the distance to
destination, location name and real time. Also, the positioning of the N -S, E -W axes or the
elevation of the route through the galleries will be represented.

Fig. 2 . Orientation and environmental data shown on the FS display

4. Experimental Setup
For general purpose illumination there are two types of LEDs commonly used: the first
one is a ph osphorus -based type, containing a blue chip and a phosphor layer, and the
second one a multicolour type, consisting of three or four independent chips.
For illumination purpose, phosphorus LEDs are preferred due to a simpler design and
lower cost, while p riority is given to multicolour LEDs for high speed data transmission
applications as they allow wavelength division multiplexing (WDM) [10]. We used in our
experimental project, the phosphorus LED as part of the transmission (oTx) module.

Fig. 3 . The VL C experimental setup
4.1. oTx LED Lighting Fixtures and Their Role in UPS and AR
To allow the LED lighting fixture to fulfil the role of a positioning infrastructure, VLC
signals have to be transmitted in a way to ensure that they do not compromise the pri mary
necessary function of lighting. The most important factors that have to be taken into
consideration are the impact on h uman vision, energy efficiency and compatibility with the
existing hardware in the fixture. Since LEDs are semiconductor devices, th e output light
can be modulated at high frequencies of MHz order, using specific frequencies modulation
techniques, as a safety measure to avoid the light flicker to be perceptible by the human
eye, while sending data at rates required for positioning [1 1].
The UPS oTx LED lighting fixture module with signal specification describes the
coding and modulation used by LED light fixtures to transmit positioning signals. The
signal is designed to be implemented in firmware that can run on low -cost microcontrolle rs
present in LED fixture drivers available on the market today.
The VLC signal sends by each LED transmit a unique identifier (ID) which
distinguishes one fixture from all other fixtures in the lighting system. The ID is stored
internally in the driver. T he map of locations of the LEDs in fixture and their IDs are
created at the time when system is build and is stored on a remote server. To determine
their own position, the wearable VLC oRx device consisting of FS on SH must sense the
LED fixture ID receiv ed through the VLC signal.
4.2. The SM FS as VLC Receiver and its Role in UPS
Due to the ID received from the LED fixture, the end -user wearing the SH with FS can
determine its position to within a one meter. Due to the incoming light signals, the ID of
fixture is decoded and the end -user’s position is determined relative to fixture as well as
position in underground gallery. Here is important to establish how to build user interfaces
for AR, based on the best practices for AR user interface design [1 2].

The graphical display on the FS’ screen is divided into seven areas of interest. It
displays in real time useful data to run a task, as for example, to save miners blocked in a
gallery following an accident (a methane explosion or celling drop).
The bottom -left is a general overview of the affected area and the additional elements
(explosion site, rescue team location, blocked galleries, location of first aid materials, and
so on). On the bottom right there is a side view of the route, with the elevation of the access
gallery to the scene of the accident. In the central area there is a detail, in 3D representation,
of the route to be followed, with additional information related to the location of the rescue
team member (the distance to the accident site and the depth at which it occurred).
A top-of -the-line view of the route, showing directions of travel, is shown in the upper
left. On the right side of the screen are displayed information taken from sensors that
monitor the concentration of gases from the points where the rescue team was located (this
information is taken from the Monitoring and Control Centre of Underground Gas
Concentrations and personalized transmitted by VLC to each end-user from underground,
according to his/her location). The top -left shows the name of the place where the end-user
is located, and the right -hand side shows both the current time and the moment when the
accident happened. The colours used to display the different information are as follows: red
indicates first -rate inform ation (explosion site, blocked galleries, dangerous gas
concentrations), blue indicates the location, route to be followed and first aid points or
accepted/safe values of gas concentration, yellow represents galleries and high level of gas
concentrations a t warning stage and orange displays gas concentrations from warning to
hazardous values.
5. Experimental Results
As long the optical channel is, the optical signal is accordingly attenuat ed. Moreover , due to
interactions with other artificial light source s, Additive White Gaussian Noises (AWGN) is
added to the original signal. Obstacles in Line of Sight ( LoS) of the signal conduct to
disturbances such as: optical power attenuation , light dispersion, polarization and
unbalanced amplification. These factors lead to random noise, which causes system
instabilit y and in extreme conditions , the VLC signal can be jitter.

Fig. 4. Signals oTx and oRx on the oscilloscope display

As observed during tests, e lectrical characteristics of the LED, such as impedance and
resistance were strongly influenced by the applied frequencies, the bias values and the
alternating signal amplitude. Following measurements of optical Signal to Noise Ratio
(SNR), this frequency, bias, alternating signal amplitude dependent impedance show s a
close correlation between LED ’s optical and electrical responses . In order to optimize the
transmission power for high illumination , different types of the orthogonal frequency
division multiplexing (OFDM ) modulation techniques [13] can be applied in o rder achiev e

a high data rate transmission . Moreover, e qualizer s can be used to remove Multi User
Interference (MUI) and Inter Symbol Interference (ISI) [14].
Signal processing techniques such as filtering can be implemented to remove additional
noises or shadows. SNR can also be improve d to optimize the optical signal strength even
in difficult environments as the underground conditions are [15,1 6].
CONCLUSIONS
The VLC technology specific for underground hazardous areas is an efficient alternative
to radi o based IPS, or other hybrid IPS technologies developed so far worldwide. We
succeeded to demonstrate de VLC communication between the LED lighting fixture and
the oRx module . This allow s a fast identification of the end -user’ position underground .
The FS and SH device with the VLC oRx attached consists in our f urther planned
enhancement of the project , in order to allow a higher secure monitor procedure for specific
environments with high explosion hazard as underground coal mining spaces are in the
presen ce of methane . The VLC oTx module consists of a PCB embedded into the lighting
fixture and the VLC oRx consists of the SH with the FS and miner’s lamp embedded. The
future work shall permit positioning signals to be transmitted by LED light fixtures to the
SH by VLC so that the end -user, wearing the SH with FS can benefit of the important data
acquired from sensors’ network underground as well as prediction of possible dangerous
situations underground, all of them displayed on the FS of the SH. With VLC emb edded
into the framework of the LED underground lighting system in the existing main galleries’
ceiling, installation and activation are simple additions that provide high value to the
mining company.
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