Intelligent Transportation Systems & Photovoltaic LiFi...

Intelligent Transportation Systems &Photovoltaic LiFi Communication SolutionEmilie Bialic 1, Cyril Chappaz 1, Frank Edme 1

1Advanced R&D division, Sunpartner Technologies, Rousset, France

February 6, 2018

1 Introduction

Over the past few decades, demand in mobility, parti-curly in individual mobility kept growing. The rapidtraffic growth is suffering from specific drawbacks. Forexample, there are more deaths and injuries, a highertraffic congestion, a massive increase in greenhousegas emissions and additional noise disturbances [3].Therefore, a permanent improvement of the transporta-tion system safety and security is required. IntelligentTransportation Systems (ITS) combine different tech-nologies to ensure both the safety and the efficiency ofthe transportation system (Figure 1). Communicationbetween vehicles (e.g. vehicle-to-vehicle, V2V), andbetween vehicles and fixed locations (e.g. vehicule-to-infrastructure, V2I) is essential [1] to transfer informa-tion in real time.

Figure 1: Illustration of ITS Communication [1]

2 Intelligent Transportation

2.1 ITS application

Intelligent transport systems apply information, dataprocessing, communication, and sensor technologiesto vehicles (including cars, trucks, trains, aircrafts andships), transport infrastructure and transport users.It allows to increase the effectiveness, environmentalperformance, safety, resilience and efficiency of thetransport system. Their deployment is made possiblethrough the rapid advances in vehicle technologies,with an increased use of sensors and a faster computerprocessing. Because of the issues raised by the differenttechnologies, it is necessary to distinguish differentlevels of vehicle autonomy systems [8, 7]:

• Level 1 : Driver Assistance Systems• Level 2 : Cooperative Systems• Level 3 : Interactive Systems

2.1.1 Driver Assistance Systems

On level 1, vehicles carry sensors that able to give in-formation from their local environment. They do notcommunicate with other vehicles, but are equippedwith advanced driver assistance systems (ADAS). Gen-erally, ADAS are developed to help the driver in thedriving process. They include by way of example :

• speed control system,• anti-lock braking system (ABS),• electronic stability constrol (ESP),• involuntary line crossing alert,• anti-collision system,• automatic emergency braking,• parking assistance and so one.

Intelligent Transportation Systems &Photovoltaic LiFi Communication Solution

2.1.2 Cooperative Systems

On level 2, cooperative systems can take into accountinformation (e.g. to improve the driving safety), tochoose the best way to reach their destination. Theyuse information obtained by infrastructure systems(I2V) such as traffic conditions, traffic works, road ac-cident and so one. The communication can only beunidirectional. The most famous cooperative system isthe global positioning system (GPS).

2.1.3 Interactive Systems

On level 3, all vehicles communicate information withlocal vehicles (V2V) and with the infrastructure sys-tems (V2I and I2V). Data analysis allows to predictaccident risks due to road traffic, road infrastrucuture,obstacles, or driver behaviors. The car is able to accessin real time to all information about the road and trafficcharacteristics. Obviously, the vehicle is equipped withADAS.

The intelligence is shared between the vehicle andthe infrastruscture through a continuous communica-tion. They share data and relevant information aboutthe road section in order to improve the security and toallow an intelligent traffic management. For example,if a vehicle senses a dangerous or critical situation, itwill use at first V2V communication to warn the ve-hicles which are around it, it will then give piece ofinformation to the infrastructure system. The centralsystem only transmits the same information to the ve-hicles which are riding towards this road section [7].Only interactive systems could allow the vehicle to befully autonomous.

2.2 Communication

Communication is a core function of interactive sys-tems. Information have to be transmitted betweensensors, control systems, user interface and networkinformation (Figure 2).

Figure 2: Communication, a core function in ITS [8]

Communication function is generally implemented

using radio frequency (RF) based technologies. Vehic-ular ad-hoc networks (VANETs) are wireless communi-cation that do not require any kind of fixed infrastruc-ture. Nowadays, vehicular ad-hoc network includesvehicles, roadside infrastructure, WiMAX (WorldwideInteroperability for Microwave Access), DSRC (Dedi-cated Short Range Communications), WiFi (WirelessFidelity), Bluetooth through which V2V and V2I safetymessages are transmitted [9]. Nevertheless, thesekinds of technologies have some issues:

• no guarantee for a high precision positioning(<50m) even using systems such as WiFi posi-tioning System (WPS),

• undesirable data packet collisions and longer de-lays could appear during traffic congestion,

• longer delay and lower data rate due to thenumber of nodes that participate in channel con-tention,

• risks of remote attacks and security issues.

Figure 3: Illustration of ITS & VLC Communication [1]

Using visible waves (390 nm-750 nm), Visible LightCommunication (VLC) and LiFi technologies havemanyinherent advantages over the RF-based DSRC technol-ogy [10], such as :

• Low complexity and cost: LED lamps are alreadyinstalled in vehicles, traffic lights and streetlights;

• High precision positioning: the VLC-based posi-tioning technology is able to reduce the positioningerror to a few centimeters;

• Improved link quality: VLC/LiFi allows to avoidthe RF problematics during traffic congestion,where only neighboring vehicles receive the perti-nent information;

• Scalability: VLC/LiFi technology considers onlya small number of neighboring vehicles;

• Security: potential attackers have to be in therange of the VLC transmission, which is signifi-cantly more difficult compared to the RF-basedtechnology.

Recent researches exploit deal with VLC/LiFi commu-nication in ITS System. For example, Dr. B. Béchader-gue [3] has studied this problematic during his PhDthesis called "Visible Light Range-Finding and Communi-cation Using the Automotive LED Lighting". The goal of

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this thesis is to evaluate a system dedicated to platoon-ing configurations that can perform simultaneously theV2V distance measurement and data transmission func-tions using the headlamps and tailights of the vehicles.

In the next section, we will talk about the potentialof LiFi communication in ITS, taking into account thespecificity of outdoor lighting environments.

3 LiFi Communication

3.1 LiFi Technology

LiFi technology uses LED light bulbs as emissionsources to carry numerical data from visible light high-frequency modulation.

Figure 4: Illustration of a LiFi Communication system

Conventionally, at the reception end, a standardavalanche photodiode (APD) converts the light inten-sity variations into an electrical signal, which is de-coded by a LiFi modem. New LiFi receivers weredeveloped by Sunpartner Technologies using semi-transparent photovoltaic modules (under the trade-mark Wysips®) directly integrated into displays (Fig-ure 5). Sunpartner streaming video demonstrator waspresented at the Mobile Word Congress 2016. Via abidirectional communication, a data rate of 5 Mbit/sin both directions was reached.

Figure 5: LiFi Sunpartner photoreceiver

3.2 LiFi & outdoor environment

The performances of LiFi optical receivers depend onseveral physical parameters of the device but also onthe LiFi and ambient lighting level. In VLC/LiFi com-munication, this issue is critical.

Figure 6: APD LiFi performances as a function of various am-bient lighting levels

If the receiver shows saturation, it deteriorates thesignal and thus the transmission is affected. In the bestcase, only the data rate decreases but in the worst one,the communication could be lost. For example, theLiFi performances of the APD C5331-5 (Hamamatsu)were registered for a LiFi level of 330 Lux at differentambient lighting levels (Figure 6).If we consider the characteristics of our LiFi demon-

strator (Figure 5) : a SNR level of 5dB is required anda spectral efficiency of about 2 bit/s/Hz is achieved.

• Indoors, until a level about 10,000 Lux (nearwindow), APD Hamamatsu has very good perfor-mances and can achieve more than 11 Mbit/s.

• Outdoors, APD C5331-5 is not efficient:

– Until a level about 21,000 Lux (cloudyweather), the APD C5331-5u can achieve lessthan 2 Mbit/s.

– More than 21,000 Lux, the communicationbreaks down.

In our knowledge, in outdoor conditions, only VLClinks are implemented for low data transfer rate (lessthan 50 kbit/s) and a camera is generally used as re-ceiver [2] because of the saturation issue. The useof photovoltaic (PV) receivers solves the saturationproblematic and improves LiFi communication in out-door conditions, allowing high data rate (upper than1Mbit/s).

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4 ITS, LiFi and Photovoltaics

4.1 Innovative photovoltaic solutions

Over the last few years, Sunpartner has characterisedin detail the performances of its PV modules by usingexperimental setups which connect a software baseddirect current optical (DCO)-orthogonal frequency di-vision multiplexing emitter and receiver to hardwareoptical front ends. These works were performed withthe support of two french research centers (CEA Letiand the laboratory IM2NP of Aix-Marseille University).

4.1.1 Robust receiver VS Saturation

In this subsection, the experiment consists in addinghuge ambient light (in Lux DC) coming from an exter-nal source to observe saturation effects [4].

Figure 7: Conventional PV modules and ambient lighting effect

Conventional LiFi PV modules have the same behav-ior than the APD C5331-5 : when ambient lightingincreases, both the Signal-to-Noise-Ratio (SNR) andthe data rate decrease (Figure 7). Nevertheless, con-ventional LiFi PV modules give better results than theAPD since they acheive 3Mbit/s until 200,000 Lux DC.

Figure 8: Wysips® PV modules and ambient lighting effect

LiFi performances of these kinds of modules are notmaintained when the ambient lighting have stronglevel range and it is not acceptable for some applica-tions such as streaming video or internet surfing. Thatis why Sunpartner technologies developed some spe-cific Wysips® PV modules for outdoor applications,

which do not suffer from saturation due to huge ambi-ent lighting (Figure 8).

4.1.2 Robust receiver VS Long distance range

Figure 9: Wysips® PV modules and distance

Both conventional and Wysips® PV modules canwork under weak LiFi signals and huge LiFi signal thatallow a long distance range of use. The distance rangedepends only on the LiFi source capacity. If the LiFisource can reach 200 Lux at 10m, the communicationcan achieve about 8Mbit/s at this distance when weuse specific Wysips® PV modules (Figure 9).

4.1.3 Robust receiver VS Shading

Due to their small surface, APDs need to be in line-of-sight of the LiFi source. But for some applications,we have to enlarge the receiver directivity. To avoid alarge number of APDs implemantation, one solutionconsists in using large PV modules, allowing detectionof various light directions. Generally, only a few part ofthe modules receive the LiFi signal. Last year, we didsome experiments to solve this issue. We shaded somearea of the PV modules and registered LiFi responses.We showed that LiFi detection was operational up to80% of shading (Figure 10).

Figure 10: Specific Wysips® PV modules and shading effects

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4.2 LiFi and Photovoltaic:The winning integration

As seen before, LiFi technology has many inherent ad-vantages for ITS. Photovoltaic receiver and particularlySunpartner’s solution has a good potential for outdoorlighting environments. Among the great advantages ofthese kinds of receivers, we can mention:

• their easy integration in any kind of surface,• an aesthetic solution : semi-transparent or design,• and the PV receiver can be used as an energy har-

vester.

At an international level, with most countries puttingin place regulations and programs aiming to limit theenvironmental impact of transportation, solar tech-nologies represents an unprecedented opportunity toreduce CO2 emissions and to extend the vehicle energyautonomy. We can mention the initiative of the Interna-tional Energy Agency that aim to analyse, recommendand promote the use of photovoltaics in vehicles andtransportation infrastructures [6].

Several prototypes of Plug-In [Hybrid] Electric Vehi-cles (P[H]EV), where the integration of photovoltaicmodules into the vehicle body is proposed, have beendesigned and are now on the road for commercialisa-tion. In 2012, Toyota was the first major automakerto offer a solar car roof option on its Prius. Reaching180W in its last model, the solar car roof would in-crease the car’s efficiency by up to 10 percent, addingup to 5 km of range per day in ideal conditions [13].Ford presented a concept car called C-Max Solar Energiat the CES 2014 [5]. More recently, Audi announced apartnership with Hanergy to put solar cells on a car roof[12]. Meanwhile, the german start-up Sono Motorsdeveloped the Sion, an electric car integrating solarcells on car roof and doors to generate further energyto cover up to 30 km per day (Figure 11) [14].

Figure 11: Photovoltaic module integration in electric cars,picture by Sono-motors

For its part, through the «Solar Smart Mobility»project, Sunpartner Technologies aims to develop andindustrialize flexible semi-transparent photovoltaicfilms integrated into glazing in order to deal with spe-cific issues related to transport applications (weight,integration, aesthetics) [15]. These films can be usedeither to power usage or required pre-conditioning of

the vehicle’s interior during parking so as to preventthe battery running out, or to autonomize local appli-cations (switchable smart glass).For VLC/LiFi communication, it means that the PV

modules integrated on main external parts of the ve-hicle could be used as receivers if correctly designed(Figure 12):

• the photovoltaic roof could receive informationthrough traffic lights and streetlights;

• the photovoltaic door could receive local data fromheadlights during an overtaking;

• the photovoltaic numberplate, hood of car, andtrunk of car could communicate with headlightsor taillights of the neighbouring cars.

Figure 12: LiFi V2V communication using PV receiver

5 Conclusion

The autonomous and semi-autonomous vehicle marketis expected to reach $500 billion by 2035[11]. Manyreal-life tests are on-going all over the word and firstcommercial applications are expected in 2020. Ma-jor companies like car makers, Google, Apple, Uberare investing huge amounts of money on that topic.Reliable and efficient communication links betweenvehicles (V2V) and between vehicles and Road infras-tructure (V2I) are necessary to the deployment of suchautonomous vehicles.

VLC/LIFI can play a significant role by bringing re-dundancy to traditional RF solutions. It brings strongvalue-added features in terms of: complexity and cost,selectivity, quality of link, high precision positioningand security. Nevertheless, one of the limitation ofLIFI existing solutions is that LIFI solutions have beendeveloped mainly for indoor applications and tradi-tional VLC/LIFI receivers do not work properly whensubmitted to sun illumination.

Sunpartner Technologies has shown that replacingtraditional VLC/LIFI detectors by specific Photovoltaicsurfaces solves the problem and allows to reach outdoorhigh speed VLC/LIFI communication while bringingpotential new features as: energy harvesting and adap-tation of the communication angle to the applicationneeds through the photovoltaic surface sizing.

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