exchange able to run the applications which

exchange between vehicles over thesophisticated wireless network can facilitate highly efficientand safe traffic environment. Under the roof ofIntelligent Transport system(ITS) many research and standardizationactivities are happening in this field.This fieldof development is broadly known as Vehicle to Everything(V2X) .It involves communication between vehicles, infrastructureand pedestrians.We are focusing on the applicationsbased on vehicle to vehicle (V2V).”A specific WiFi modeoperating in the 5.9 GHz frequency band, formerly knownas the p amendment of the IEEE 802.11 standard, enables adhoccommunication and the direct exchange of informationamong vehicles in their vicinity, including the communicationbetween vehicles and the roadside infrastructure” 3.This wireless standard capable of providing direct and lowlatency communication between vehicles in a highly mobileenvironment. The vehicles are communicated through adevice called on board unit(OBU) which is embedded ineach vehicle and capable of transmit/ receive messages.Thedevice should also able to run the applications which canprocess the received information and provide meaningfulsignals to the drivers. V2V applications are also useful forthe future autonomous vehicles.2 CAR2CAR ARCHITECTURE 15THE Car to car system follows a layered architecture andeach layeris consist of different protocols.The standardizationprocess has happened parallel in the US and Europeand resulted in two different standards called Dedicatedshort range communication(DSRC) and C-ITS respectively.DSRC is based on the widely accepted WLAN standardIEEE 802.11-2012. An amendment to this standard calledIEEE802.11p defines the Physical layer(PHY) and Mediumaccess layer(MAC). In US standard the IEEE 1609 seriesof standards on top of IEEE 802.11p combined to formthe stack of standards called Wireless Access VehicularEnvironment (WAVE) 9 10.IEEE 802.11p is similar toIEEE802.11 a . The main difference is that IEEE 802.11p Department of Computer science, T U Chemnitz.E-mail: [email protected] 20, 2018;Fig. 1. V2Xworks on 10 MHz channels at 5.9GHz frequency band.The IEEE 802.11p standard utilizes Orthogonal FrequencyDivision Multiplexing modulation(OFDM) technique whichis a multi-carrier digital modulation technique. In OFDM,the different frequency signals are split into several narrowbandchannels. The 75 MHz frequency is divided intoseven 10 Mhz channels and in which one channel is controlchannel and others are service channels. Each channel havedifferent functionality and transmit powers values. Thecontrol channels has the maximum transmit power 14. Toachieve the low-latency requirements, 802.11p introducedOutside the Context of BSS (OCB). The OCB mode appliesto any two or more devices within the coverage area of asingle radio link. A STA in OCB mode can send and receivedata and control frames anytime without forming or beinga member of any SS. 8The MAC layer of 802.11p utilizesenhanced distributed channel access(EDCA) defined inIEEE802.11e for the prioritization of safety and time-criticalmessages.DSRC utilizes time/frequency division multipleaccess to the seven channels which is defined in IEEE 1609.4standards. The concept is that the time is divided into 100ms slots in which 50 is allocated for control channel andrest is for the service channels.The control channels are usedto broadcast the high priority safety messages and channelmanagement information which allow receiver to switch toJOURNAL OF LATEX CLASS FILES, VOL. 14, NO. 8, AUGUST 2015 2the required service channel.Service channels transmit nonsafety critical messages. IEEE 1609.3 standard defines theWave short message protocol(WSMP) which is a less overheadmessage used for sending messages through controlchannels. WSMP messages can directly change the lowelevel radio parametes. The non safety messages transmittedthrough service channels utilizes IPv6 Protocol 13. In CITSstandard a ad-hoc routing protocol is defined calledGeonetworking which can address and forward messagesbased on their geographical locations 10. The security layeris defined in IEEE 1609.2 standards which facilitates anpublic key based encryption and authentication.On top ofnetwork layer the SAE standard J2735 defines the messagesformats for information exchange between vehicles. In USstandard The Basic safety messages which transmits vehiclestate information in 10 Hz frequency.Even though the state of the art communication technologyfor V2V is IEEE 802.11p based Wireless standard thereare other communication technologies are also consideringfor V2V. The LTE D2D is considered as a competitor whichcan also facilitate the direct communication between vehicleswith lower latency. The upcoming 5G standards areexpected to accommodate the need of V2V communications.2.1 Car2Car applicationsBased on the ability to address the safety issues, commercialand technical aspects a set of applications are selected asthe basic set of applications (BSA ) as V2V features. Theapplications are mainly grouped under classes called Activeroad safety, Cooperative traffic efficiency, co-operative localservices, and global Internet services.These applications arecalled day 1 features in EU and selected for development bythe Amsterdam Group. These applications are selected asrelease 1 application in US. Active road safety applicationsare highly time constrained and latency range is between 10and 100 ms. These set of applications are primarily focusedon road safety. The V2V release 1 applications plays in amajor role in Level1 and level 2 fo automation defined bySAE. The level 1 is driver assistance and level 2 is partialautomation. V2V communications also offer an operationalrange of up to 300 meters between vehicles to facilitate identificationof intersecting paths that may potentially result ina crash if no driver or vehicle action is taken.Fig. 2. Basic application setSome of the important applications of this class areEmergency electronic brake lights which allows a vehicleto inform its following vehicles about a hard breakingsituation. Safety function out of normal condition warning issimilar but it allows vehicle to notify any malfunction in thevehicle to the other vehicles The Co-operative awareness applicationallows to notify other vehicles about an emergencyvehicle, slowly moving vehicle and motorcycle presence.Intersection collision warning is an important applicationwhich inform a vehicle about the chance of a collision atan intersection due to another vehicle. Wrong way drivingwarning, Stationary vehicle – accident, Stationary vehicle -vehicle problem, Traffic condition warning, Signal violationwarning Roadwork warning, Collision risk warning, andDecentralized floating car data are some of the importantuse cases selected under road hazard warnings. The primarygoal of the applications selected under the Cooperative trafficefficiency class is traffic fluidity ?. To facilitate these applicationsV2V facilitate layer defines few message formatsto send the vehicle information to other vehicles. In US standardmost important message is Basic safety message (BSM) which is periodically transmitted in a frequency of 10 Mhzmaximum. The message similar to BSM in C-ITS standardis Cooperative awareness message (CAM ) which containscritical vehicle state information which can be used by theapplications to calculate vehicle movement and position.Distributed Environmental Notification Message (DENM)is another kind of message transmitted by the applicationwhen an event happens. The applications run on the OBUwill evaluate the received messages and provide the suitableinformation to the user. Position data,Vehicle speed, Drivingdirection are part of the messages that are mandatory. Thereis need of other data such as Hazard warning signal flasher,Brake power / vehicle deceleration,ABS, ESP and ASRsensors, Rain sensor / wiper status which are required forspecific basic applications but they are optional in messageformat.The BSA is the first focus for developing relevant standardsand their associated conformance testing procedures.Then some Enhanced Set of Applications (ESA) can bedefined to improve road safety, traffic efficiency while maintaininga positive business model for involved stakeholders.bsa The Basic set of applications are expected to startdeploy by 2020.3 CONCLUSIONThe 802.11p based WLAN standard is the most dominantcommunication standard used for V2V applications. Cellulartechnologies such as LTE and 5G are also consideredfor V2V but mainly for non-safety applications.The basic setof applications are mainly focus on road safety and trafficefficiency. To contribute to the higher levels of automationthe performance requirements of V2V communication has toimprove in terms of reliability latency and security. Securityis one of the most critical aspect which need solid solutions.

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