4,556 research outputs found
Comparison of Radio Frequency and Visible Light Propagation Channels for Vehicular Communications
Recent research has shown that both radio and visible light waves can be used to enable communications in highly dynamic vehicular environments. However, the roles of these two technologies and how they interact with each other in future vehicular communication systems remain unclear. Understanding the propagation characteristics is an essential step in investigating the benefits and shortcomings of each technology. To this end, we discuss salient properties of radio and visible light propagation channels, including radiation pattern, path loss modeling, noise and interference, and channel time variation. Comparison of these properties provides an important insight that the two communication channels can complement each other’s capabilities in terms of coverage and reliability, thus better satisfying the diverse requirements of future cooperative intelligent transportation systems
Impact of Vehicle Headlights Radiation Pattern on Dynamic Vehicular VLC Channel
This article develops a statistical large-scale fading (path loss) model of a dynamic vehicular visible light communication (VVLC) system. The proposed model combines the impact of inter-vehicle spacing and the radiation intensity distribution as a function of the irradiance angle which changes with the traffic conditions. Three models (Lambertian, Gaussian, and empirical) are utilized to examine the impact of vehicles headlights radiation pattern on the statistical path loss of VVLC system. The analytical model of channel path loss is validated by Monte Carlo simulation with the headlight model simulated with a raytracing software. The path loss values of the Gaussian model differ by 2 dB compared to the Lambertian model, irrespective of the traffic conditions while it differs by 24.6 dB during late night and 8.15 dB during rush hours compared to the empirical model of a Toyota Altis headlight. This variation shows that the radiation intensity distribution should be modelled for each vehicle's headlights from each manufacturer to ensure accurate VVLC channel model. The proposed Gaussian model provides a close approximation to describe such radiation pattern and can easily be adapted to model for different manufacturers' headlights
The Dynamics of Vehicular Networks in Urban Environments
Vehicular Ad hoc NETworks (VANETs) have emerged as a platform to support
intelligent inter-vehicle communication and improve traffic safety and
performance. The road-constrained, high mobility of vehicles, their unbounded
power source, and the emergence of roadside wireless infrastructures make
VANETs a challenging research topic. A key to the development of protocols for
inter-vehicle communication and services lies in the knowledge of the
topological characteristics of the VANET communication graph. This paper
explores the dynamics of VANETs in urban environments and investigates the
impact of these findings in the design of VANET routing protocols. Using both
real and realistic mobility traces, we study the networking shape of VANETs
under different transmission and market penetration ranges. Given that a number
of RSUs have to be deployed for disseminating information to vehicles in an
urban area, we also study their impact on vehicular connectivity. Through
extensive simulations we investigate the performance of VANET routing protocols
by exploiting the knowledge of VANET graphs analysis.Comment: Revised our testbed with even more realistic mobility traces. Used
the location of real Wi-Fi hotspots to simulate RSUs in our study. Used a
larger, real mobility trace set, from taxis in Shanghai. Examine the
implications of our findings in the design of VANET routing protocols by
implementing in ns-3 two routing protocols (GPCR & VADD). Updated the
bibliography section with new research work
Vehicular Visible Light Communications: The Impact of Taillight Radiation Pattern
We investigate the path-loss of vehicular visible light communications based on the radiation pattern of a commercial car taillight. The measured pattern is incorporated into a ray-tracing model and simulation results indicate up to 4.2 dB variation in the path-loss compared with the Lambertian model
Towards an optical wireless communication based Vehicle to Vehicle Communication System
Vehicle to Vehicle (V2V) Communication is a developing technology that aims to make road transportation systems intelligent, to avoid accidents and traffic congestions. This thesis presents Optical Wireless Communication (OWC) as a solution that will drive the next generation of V2V systems. The current standards for V2V and vehicle to infrastructure (V2I) communication, based on radio frequency techniques, are revised. Also, the current standard for Visible Light Communication (VLC), IEEE 802.15.7 is analyzed. This project also shows the first steps towards a cost-effective implementation of V2V VLC taking advantage of already available hardware in vehicles. Finally, a transmission system is presented aiming to demonstrate an adaptation of current VLC standards for V2V and V2I communication. Another system based on IR communication is also presented. These are presented as an alternative for V2V and V2I solutions based on radio frequency techniques, opening the door to a relevant industrial application of optical wireless communication
Vehicular VLC: A Ray Tracing Study Based on Measured Radiation Patterns of Commercial Taillights
In this paper, we investigate the performance of vehicular visible light communications based on the radiation patterns of different commercial taillights (TLs) using non-sequential ray tracing simulations. Our simulation results indicate a significant variation in the path loss compared with Lambertian model. Based on the ray tracing results, we propose a new path loss model as a function of the propagation distance considering the asymmetrical radiation pattern of TLs. We use this model to derive the attainable transmission distance. We further present the delay spread for various vehicular communication scenarios to demonstrate the effect of neighboring vehicles
Fundamental Analysis of Vehicular Light Communications and the Mitigation of Sunlight Noise
Intelligent transport systems (ITS) rely upon the connectivity, cooperation and automation of vehicles aimed at the improvement of safety and efficiency of the transport system. Connectivity, which is a key component for the practical implementation of vehicular light communications (VeLC) systems in ITS, must be carefully studied prior to design and implementation. In this paper, we carry out a performance evaluation study on the use of different vehicle taillights (TLs) as the transmitters in a VeLC system. We show that, the transmission coverage field of view and the link span depend on TLs illumination patterns and the transmit power levels, respectively, which fail to meet the typical communication distances in vehicular environments. This paper proposes an infrared-based VeLC system to meet the transmission range in daytimes under Sunlight noise. We show that, at the forward error correction bit error rate limit of 3.8 10^-3, the communication distances of the proposed link are 63, 72, and > 89 m compared with 4.5, 5.4 and 6.3 m for BMWs vehicle TL at data rates of 10, 6, and 2 Mbps, respectively
Medium access control protocol for visible light communication in vehicular communication networks
Recent achievements in the automotive industry related to lighting apparatuses include the
use of LED or laser technology to illuminate the vehicle environment. This advancement resulted
in greater energy efficiency and increased safety with selective illumination segments.
A secondary effect was creating a new field for researchers in which they can utilize LED
fast modulation using the Pulse Width Modulation (PWM) signal. Using LED to encode and
transmit data is a relatively new and innovative concept. On the other field, there have been
advancements in vehicular communication using radio frequency at 2.4 or 5GHz. This research
focuses mainly on a field in which visible light augments or replaces radio frequency communication
between vehicles.
This research also investigates the effect of asymmetry on network performance using Visible
Light Communication (VLC) in vehicular networks. Different types of asymmetry were defined
and tested in real-world simulation experiments. Research results showed that asymmetry has
a negative influence on network performance, though that effect is not significant.
The main focus of the research is to develop a lightweight and new Media Access Control
(MAC) protocol for VLC in vehicular networks. To develop a MAC protocol for VLC, special
software was developed on top of the existing Network Simulation Environment (NSE).
A new VLC MAC protocol for Vehicle to Vehicle (V2V) was benchmarked using a defined set
of metrics. The benchmark was conducted as a set of designed simulation experiments against
the referent IEEE 802.11b MAC protocol. Both protocols used a newly defined VLC-equipped
vehicle model. Each simulation experiment depicted a specific network and traffic situation.
The total number of scenarios was eleven. The last set of simulations was conducted in realworld
scenarios on the virtual streets of Suffolk, VA, USA.
Using defined metrics, the test showed that the new VLC MAC protocol for V2V is better than
the referent protocol.Nedavna dostignuća u automobilskoj industriji koja se tiču opreme za osvjetljivanje uključuju
korištenje LED ili laserskih rasvjetnih tijela za osvjetljivanje okoline. Ovime se postižu uštede u
potrošnji energije kao i povećana sigurnost u prometu. LED rasvjeta je uniformnija od običnih
žarulja tako da osvjetljenje bude ravnomjernije i preciznije. Obzirom da su LED selektivne
moguće je odabrati segment ceste koji se želi osvijetliti. Upravo ta fleksibilnost LED otvara
novi prostor za istraživače gdje mogu koristiti PWM signal za modulaciju podataka. PWM
je poseban signal koji ima varijabilnu širinu pulsa na izlazu. Istraživači i znanstvenici mogu
koristiti LED za kodiranje i prijenos podataka između automobila. Prednosti korištenja komunikacije
u vidljivom dijelu elektro-magnetskog spektra (eng.VLC) je u činjenici da taj segment
nije zaštićen licencama te je otvoren za slobodno korištenje. Osim toga, vidljivo, neintenzivno
svjetlo nema biološki negativnih posljedica. Kod korištenja PWM signala za modulaciju, postojeći izlaz svjetla i njegova funkcija (osvjetljivanja ceste) nisu narušeni. Ljudsko oko ne može
detektirati oscilacije tako visoke frekvencije (oko 5 kHz)
S druge strane, komponente koje mogu primiti poslani signal su foto diode ili kamere. Kamere
su već prisutne na modernom vozilu u obliku prednje kamere ili stražnje kamere za pomoć pri
parkiranju. U svakom slučaju, tehnologija je već prisutna na modernom vozilu.
Na drugom području, znanstvenici rade na komunikaciji između vozila koristeći radio valove
niže frekvencije 2.4 ili 5 GHz. Komunikacija između automobila je predmet standardizacije i
mnoge zemlje već propisuju pravila za obaveznu ugradnju opreme za takav oblik komunikacije.
Prednost takvog koncepta je razmjena podatka; od onih za zabavu pa do kritičnih i sigurnosnih
podataka npr. informacija o nadolazećem mjestu gdje se dogodila prometna nesreća.
Ovo istraživanje se fokusira na proširenje ili zamjenu radio komunikacije sa komunikacijom
koristeći vidljivi dio spektra (npr. LED i kamere). Jedan od glavnih nedostataka takvog koncepta
je ne postojanje adekvatnog i specijaliziranog protokola za kontrolu pristupa mediju
(eng. MAC). Drugi problem je nepoznati efekt asimetrije u VLC komunikaciji na performanse
mrežne komunikacija. Ovo istraživanje je prepoznalo i klasificiralo različite tipove asimetrije.
Svaki tip je testiran u sklopu simulacijskog eksperimenta u stvarnim scenarijima. Pokazalo se
je da asimetrija negativno utječe na mrežne performanse, međutim taj efekt nije značajan jer
uzrokuje manje od 0.5 % neuspješno poslanih poruka.
Glavni fokus istraživanja je razvoj novog i pojednostavljenog MAC protokola za VLC komunikaciju
između automobila. Kako bi se razvio novi MAC protokol nad VLC tehnologijom u
prometnim mrežama, bilo je nužno napraviti i novu razvojnu okolinu koja se bazira na postojećim mrežnim simulatorima. Novi VLCMAC protokol za komunikaciju između automobila je
testiran koristeći definirani set metrika. Testovi su napravljeni u obliku simulacijskih eksperimenata
u kojima su uspored¯ivane performanse novog i referentnog protokola. Referentni protokol,
u ovom istraživanju je IEEE 802.11b MAC protokol. U sklopu ovog rada definiran je i model
vozila opremljen VLC tehnologijom. U simulacijskim eksperimentima je korišten isti model
vozila za oba protokola. Za potrebe istraživanja je definirano jedanaest simulacijskih eksperimenata,
svaki od njih opisuje specifične situacije u mrežnim komunikacijama kao i u prometu.
Završni simulacijski scenariji uključuju okolinu iz stvarnosti, mreža ulica grada Suffolka, SAD.
Osim stvarnih ulica, vozila su se kretala i razmjenjivala podatke koristeći mrežnu komunikaciju
na kompletnom ISO/OSI mrežnom stogu sa zamijenjenim MAC podslojem.
Razvojna okolina uključuje preciznu provjeru fizičkih karakteristika na razini putanje zrake
svjetlosti. Ova preciznost je bila nužna kako bi simulacije bile što vjerodostojnije stvarnim sustavima.
Obzirom da se radi o mnogo kalkulacija, obično računalo nije dostatno za izvođenje
simulacijskih eksperimenata; zbog toga su se eksperimenti izvodili na klasteru računala Sveučilišta
u Zagrebu.
Koristeći definirane metrike, istraživanje je pokazalo kako je novi VLC MAC protokol za komunikaciju
između automobila bolji od referentnog protokola.
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