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Realization of Anti-collision Warning Applicationusing V2V Communication!

Woong Cho, Kyeong-Soo Han, Hyun Kyun Choi and Hyun Seo OhElectronics and Telecommunications Research Institute (ETRI), Rep. of Korea, 305-700

Emails: {woongcho. kshan. choihk. hsoh5}@etrLre.kr

Abstract- Vehicular communications provide new conver­gence applications by combining vehicles and communicationtechnologies. In thi s paper, we consider the anti-collision warn­ing application using vehicle-to-vehicle (V2V) communication.First, we introduce the general and special features of the over­all system and specifications of the communication prototype.Then, we investigate the application scenarios and communica­tion algorithms including practical measurement results. Someimplementation issues of vehicular communications are alsoaddressed.

Jndex Terms-Vehicular communications, vehicle safety,anti-collision warning

I. INTROD UC TION

Vehicular communications have been receiving much at­tention in both intelligent transportation system (ITS) andcommunications area . By applying communication technol­ogy with vehicular environments, vehicular communicationsprovide various applications such as anti-collision warning,probe data collection, intersection safety, traffic information,roadwork warning, multimedia downloading and internetaccess. These applications can be implemented via vehicle­to-vehicle (V2V) or vehicle-to-infrastructure (V2I) commu­nication. Among various applications, public safety is oneof the important applications. Protocols for vehicle safetyapplications have been discussed in [2], [15], and reliabilityanalysis for safety applications has been introduced in [I]based on measurement data. In [12], a theoretical latencyof V2V communication for rear-end collision avoidanceis calculated. Many ITS related projects consider safetyapplications as a major service, such as cooperative vehicle­infrastructure systems (CVIS), SAFESPOT, Pre-drive C2X,COOPERS, IntelliDrive and etc., [4], [5], [9], [13], [14].

In addition to ongoing research and projects , standardiza­tion proc esses for ITS are also carri ed out by several institu­tions . IEEE try to set up standards for vehicular communi­cations, namely Wireless Access in Vehicular Environments(WAVE), which includes standards for PHY/MAC and upperlayers named as IEEE 802.11P and IEEE 1609.x, respec­tively [8], [16]-[20]. The IEEE 802.llp specifies detail edoperation of PHY/MAC in 5.90Hz frequency band. While ,the IEEE 1609.x deals with resource managers, securityservices, networking services and multi-channel operation.

t This work is supported by the IT R&D program of MKEIIITA [2007­1'-039-01, Vehicle Multi-hop Commun ication Technology Development]

Besides, European telecommunications standards institute(ETSI) TC ITS develops European profil e based on theIEEE 802.11 PHY [7]. International organi zation for stan­dardization (ISO) TC204 WO 16 focuses on multiple mediamanagement which is called Communications Access forLand Mobiles (CALM). Although these standards for ITSare still developing, most of basic the PHYIMAC structurefollow the IEEE 802.11 standard especially in 50Hz ITSfrequency band (5.855-5.9250Hz).

To realize safety applications in vehicular communica­tions , some basic requirements need to be satisfied. Commu­nication schemes support both broadcasting and unicastingdepending on the specific application. Latency has to be veryshort since the processing time is critical in safety applica­tions. Communication networks need to provide both V2Vand V21 communications with high mobility. In summary,the following basic requirements are necessary for safetyapplications:

• Communications: Broadcasting, Unicasting• Latency: Less than 100msec• Networking: V2V/V21 (I2V)• Mobility: Up to 200km/h

In this paper, we develop an anti-collision warning systemusing V2V communication, which is one of the safetyapplications.

The rest of this paper is organized as follows. The overallsystem architecture of developing vehicular communicationsystem is described in Section II. In Section III, the specificsystem parameters are introduced. The Anti-collision warn­ing application including measurement results of communi­cation performance and implementation issues is presentedin Section IV, and concluding remarks are given in SectionV.

II. SY ST EM CO NFIG UR ATION

Fig. I depicts the overall system architecture. The over­all system consists of antenna, VMC on-board-equipment(OBE), vehicle terminal and road-side-equipment (RSE).Antennas of the vehicle and the infrastructure are omni­directional and support 5.83-5.900Hz frequency range. OBEand RSE have the communication module which is equippedwith Modem, MAC and RF module. The vehicle terminaldisplays the information of my vehicle and adjacent vehi­cles by using OPS and the communication module. OBE

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provides both V2V and V2I communications, and multi-hopcommunication is also supported. RSE is connected to theITS center which collects, processes and reroutes the trafficinformation from vehicles or other RSEs.

Vehicleterminal a BE

Fig. I. Overall system architecture

Powe r

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r--·--·_·--l~~

GPS Modu le ,1",111

Processor

I ( GPS connector) IL_. ._..J

Fig. 2. Communication platform structure

A. General features

With aforementioned system architecture, our system hasthe following general features:

• RF frequency: 5.8GHz band• Channel bandwidth: IOMHz• Modulation: OFDM (BPSK, QPSK, I6QAM)• MAC protocol: Time slot based CSMA/CA, EDCA• Routing: Position based• Service platform OS: Window CE 5.0

Since we use a commercial RF chip, the range of RFfrequency depends on the chip specification, and the RFmodule supports 5.850-5.90GHz. With IOMHz signal band­width, data rate is supported up to 12Mbps. MAC protocoladopts the carrier sense multiple access/collision avoid­ance (CSMA/CA) and enhanced distributed channel access(EDCA) . We also use the time slot based CSMA/CA MACprotocol which will be discussed in the following subsection.Routing protocol is based on the position and mobile terminaluses Window CE 5.0 OS. Our system is compatible withthe IEEE 802.11P except for supporting frequency band andchannel bandwidth. The frequency band of the IEEE 802.11Pis 5.850-5.925GHz, and the IEEE 802.11P defines 5 and20MHz channels besides 10MHz channel [8].

B. Special features

In addition to the general features, our system has twounique features in PHY and MAC compared with the IEEE802.11p. The IEEE 802.11P uses the preamble based channelestimation without any modification of the IEEE 802.11scheme. The preamble based system is suitable for shortpacket transmission but not sufficient for long packet trans­mission since channels change rapidly in vehicular envi­ronments. The CSMA/CA, which is the MAC protocol ofthe IEEE 802.11p, has a potential problem of collisions,and this problem is more critical in broadcasting comparedwith unicating. It is worth mentioning that most of safetyapplications use broadcasting [6]. As the number of nodesincreases, the probability of collisions also increases. In realvehicular environments, collisions may cause serious prob­lems in safety applications. Another problem of CSMA/CA

is fairness. Since V2I communication has unbalanced band­width requirement depending on transmitter, differentiatedchannel access priority is required between RSEs and OBEs.However, CSMA/CA cannot distribute the accesses withpriority. To solve these problems, we suggested the followingtwo schemes in PHY and MAC.

• PHY: Midamble based channel estimation• MAC: Hybrid MAC (time slot based CSMA/CA)

The basic idea of the midamble is to insert training sym­bols periodically between the data symbols, which enablescontinuous channel tracking. The initial channel informationis captured by the preamble, and periodic update of channelinformation is carried out by the midamble. In Hybrid MAC,different contention window size can be assigned to eachnode with slot ownership, thus each node selects its own timeslot. It is shown that this MAC protocol increases throughputespecially in broadcasting. For more detailed mechanism andsome simulation results of midamble and hybrid MAC, werefer the readers to [3], [10], [11].

III. SYSTEM SPECIFICATIONS

In this section, we will describe the detailed systems whichinclude communication platform, RF module/antenna andvehicle terminal.

A. Communication platform

Fig. 2 shows the structure of communication platform.Communication platform consists of several devices: FPGA,processor, RF module , ADC/DAC, GPS module, memoryand power unit. The FPGA performs hardware process ofcommunication module, and the processor deals with soft­ware of communication module and connection with outsideinterfaces. The RF module is used for down-conversion andup-conversion ofRF signal and baseband signal, respectively.DAC transforms digital signal of FPGA to analog signal,and vice versa for ADC. There are three types of memory,i.e., SDRAM, Flash and EEPROM, where the processor usesSDRAM and Flash, and FPGA uses EEPROM for systemconfiguration. Input voltage is 12V since communicationplatform is built into a vehicle, and power devices create

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various voltage levels, i.e., 3.3V, 2.5V, 1.8V, 1.2V, whichare supplied to several devices depending on their powerrequirement. GPS provides pulse per second (PPS) signalto the processor, and is also used for informing vehiclespeed, location and direction. Outside interfaces support RS­232, LAN and USB. With this communication platform,the following IEEE 802.11P PHY standard (table l) issupported . Notice that our system can support both the IEEE802.11P standard and the advanced feature as described inthe previous section.

TABLE I

IEEE 802.11 I' STANDARD (I OMI-Iz BA NDWIDTH) .

Parameter ValueBandw idth 10 MHzFFT size 64# of data subcarriers 48# of pilot subcarriers 4# of subcarriers(total) 52 (48+4)subcarrier frequen cy spacing 0.15625 MHzSignal bandwidth 8.28 MHzIFFT/FFT period 6.4 J-LSGI duration 1.6 J-LSSymbol interval 8.0 (6.4+ 1.6) J-LS

B. RF module and antenna

The RF module is designed to support 5.850-5.890GHzusing the MAX2829. The MAX2829 adjusts receiver gainby setting receiver variable gain amplifier (VGA) registerand low-noise-amplifier (LNA) which has three adjustablelevels. By combining the MAX2829 receiver path gain withoutside LNA, the RF module provide -85dBm sensitivity forBPSK (convolution encoder rate with 1/2) modulation, andthis value satisfies the IEEE 802.11P standard. The maximumequivalent isotropically radiated power (EIRP) is 23dBmand the stabilized RF module output provides approximatelyclass C transmit spectrum mask of the IEEE 802.11p. TheOmni-directional antenna with 8dBi gain is used both forRSE and aBE. The detailed antenna specifications are de­scribed in table II. By practical measurements, it is verifiedthat our system can transmit signal up to 1.6km with lessthan 5% of packet error rate (PER) for all modulationschemes, i.e., BPSK, QPSK and 16QAM. Our system hasapproximately lms of link setup time and several ms oflatency depending on the packet length.

TABLE II

A NTENNA SPECIFI CATIO N .

ITEM Spec ificationFrequency range 5.83-5.89GHzGain 8dBi (± 1)V.S.W.R ::; 1.5-3dB beam width 150 ± 2°Polarization VerticalNorm al impedance 500Max power 1 Watt

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I Vehicle VMC aB E Antenna I

: terminal • :I • II . II :-- II Il ~ J

\ I\ I

V2V "" V2V--z.-- ' --z.--~~ ~

Fig. 3. Anti-collision warning scenario

GPS modu le

•Driving statusmanageme nt

module

-.V2V vehicletermi nal API

-.-V2V

co mmu nicationmodule

Fig. 4. SS/SA transmission diagram

C. Vehicle terminal

The vehicle terminal consists of vehicle terminal platformand services . The vehicle terminal has Window CE 5.0 oper­ating system and provides application programming interface(APl) between the services and the vehicle terminal platformfor transmitting and receiving safety messages. Vehicle infor­mation such as speed, location, direction and driving path canbe collected by the vehicle terminal platform combined withGPS. The collected information are analyzed and informedto user by display and sound. The vehicle terminal providesseveral services such as anti-collision warning, roadworkwarning, intersection safety and traffic information collec­tion. The former two services and the later two services arebased on V2V and V21 communications, respectively. Weconsider the anti-collision warning application in this paper.

IV. A NTI-COL LISION WAR NI NG APPLICATION

In this section, we introduce the anti-collision warningapplication. We describe measurement results of communi­cation performance, detailed application scenarios and thecommunication algorithm . Based on practical field tests,some implementation issues are also addressed.

A. Communication Performance

In this subsection, we present measurement results of V2Vcommunication in terms of communication range, latencyand packet error rate (PER). The results is obtained in afreeway environment where only two vehicles are present atthe freeway. We use QPSK for all tests.

Copyright © 2009 IEEE

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Fig. 5. SS/SA receiving diagram

I) Communication range: In this test, we record themaximum communication range between two vehicles.

• Measurement setup: One vehicle is fixed and the othervehicle moves towards the fixed one from 2km away. Themoving vehicle continuously sends a packet until the fixedvehicle receives the packet, and the distance is recorded asthe communication range. We use packet size of 512 bytesand various test speeds, i.e., 20km/h, 60km/h, 100km/h,120km/h.

• Results: The correct reception starts when the movingvehicle passes approximately 1.6km distance from thefixed vehicle regardless of the vehicle speed. We use23dBm EIRP with 8dBi antenna gain for both vehicles.

2) Latency: As we indicate earlier latency is critical factorfor reliable communication especially in safety applications.

• Measurement setup: At first, two vehicles are locatedapproximately 2km away from each other. Then, bothof them start to move simultaneously with oncomingdirection. We measure latency when the distance betweenthe two vehicles is 500m. We consider various packetlengths (512, 1024 and 1518 bytes) and vehicle speeds(30km/h , 60km/h, 90km/h and 120km/h). Notice that thecorresponding relative speeds of two vehicles are 60km/h,120km/h, 180km/h and 240km/h, respectively.

• Results: The measured latency is represented in Table. III.The results show that latency is enough to implementsafety applications although latency is increasing as thepacket lengths increase.

3) PER: PER is also an important criterion for reliablecommunication. We measure the PER with unicasting.

• Measurement setup: We adopt the same setup as in latency

TABLE III

LATE NCY.

Vehicle/relative speed 512bytes 1024bytes 1518bytes30/60 km/h 2.8ms 4.7ms 6.7ms60/120 km/h 2.8ms 4.8ms 6.8ms90/180 km/h 3.3ms 5.1ms 7.5ms120/240 km/h 3.0ms 5Ams 7.3ms

measurement. The only difference is that 2000 packets aresent from one vehicle to the other vehicle to count the errorpackets instead of sending a single packet.

• Results: The PER of the worst case is 0.1%, whichcorresponds to 1998 reception out of 2000 transmission.However, this result does not count the retransmissionnumber in unicasting. If we consider the retransmission asan error, the PER will increase compared with this result.

Above results show that our system is reliable for safetyapplications. However, it is worth mentioning that the perfor­mance will be worse in realistic environment which consistsof hundreds vehicles, obstacles and building .

B. System description

With V2V communication, we implement the anti­collision warning application by multi-hop communication.V2V communication is a distinct communication schemewhich supports ad-hoc communication without any infras­tructure. This application can prevent consecutive collisionsby informing emergency situation in advance.

The anti-collision warning scenario is depicted in Fig. 3.We consider two scenarios, which are sudden stop (SS) andsudden acceleration (SA). SS or SA occur when vehiclespeed abruptly decreases or increases, respectively. In SSor SA scenarios, safety messages are generated by vehicles,and these messages are transmitted to the following/frontvehicles by multi-hop communication. When adjacent vehi­cles approach to a certain range of my vehicle by SS orSA, the warning message is generated in both my vehicleand adjacent vehicles. Very emergency warning is generatedif the adjacent vehicles move very close to my vehicle.Otherwise , the warning messages disappear.

Figs. 4 and 5 represent transmission and reception diagramof SS/SA messages, respectively. At the transmission side,the driving status management module monitors the statusof vehicles. If a vehicle increases or decreases the vehiclespeed, SS or SA message is generated in a certain condition.This message is transmitted to adjacent vehicles through thevehicle terminal API and communication module. The crite­ria of message generation can be adjustable by programmingthe driving status management module. At the receiver, thedriving status management module and adjacent informationmanagement module monitor SS or SA from the adjacentvehicles. If SS or SA message is received, the driving statusmanagement module analyzes the received information andlet the warning information process engine know. Then,the warning information process engine decides whether the

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Fig. 6. V2V service terminal

[I I F. Sai and 1-1 . Krishnan, "Reliability analysis of DSRC wirelesscommunication for vehicle safety applications," Proc. of IntelligentTransportation Systems Conference, pp. 355-362, 2006.

[2] S. Biswar, R. Tatehikou and F. Dion, "Vehicle-to-Vehicle wirelesscommunication protocols for enhancing highwary traffic safety," IEEECommun. Mag., vol. 44, no. I, pp. 74-82, Jan. 2006.

[3] W. Cho, S. I. Kim, H. K. Choi, H. S. Oh and D. Y. Kwak, "Perfor­mance evaluation ofV2VIV21 communications: the effect of midambleinsertion," Proc. of Wireless Communications, Vehicular Technology,Information Theory and Aerospace & Electronic Systems Technology,pp. 793-797, 2009.

141 COOPERS hompage, http://www.coopers-ip .eu[5] CVIS project homepage , http://www.cvisproject.org[6] "The CAMP Vehicle Safety Communications Consortium , Vehicle

Safety Communications Project Task 3 Final Report," U.S. Departmentof Transportation , 2005.

[7] "Intelligent Transport Systems ; European profisle standard on thephysical and medium access layer of 5GHz ITS," ETSI ES 202 663VI.I2, 2009.

[8] IEEE 1'802.I Ip/D8.0-2009 , Draft standard for information technology- telecommunications and information exchange between systems ­local and metropolitan area networks-specific requirements , Part I I,Amendment 7: Wireless Access in Vehicualr Environments, 2009.

[9] IntelliDrive homepage, http://www.intellidriveusa.org[10] S. I. Kim, 1-1 . S. Oh, and H. K. Choi, "Mid-amble aided OFDM

performance analysis in high mobility vehicular channel," Proc. ofIntelligent Vehicles Symposium, pp. 751-754, 2008.

[I I] S. Lee, W. Cho, H. S. Oh and D. Y. Kwak, , Available at IEEE doc­uments server, https:l/mentor.ieee.org/802.1 I/documents, document#IEEE 802. I 1-08/1273rl.

[12] M. Nekovee, "Quantifying performance requirements of vehicle-to­vehicle communication protocols for rear-end collision avoidance,"Proc. of Vehicle Technology Coriference-Spring, pp. 1-5, 2009.

[I3] PRE-DRIVE C2X homepage, http://www.pre-drive-c2x .eu[I4] SAFESPOT integrated project homepage, http://www.safespot-eu .org[15] X. Yang, 1. Liu, F. Zhao and N. H. Vaidya, "A vehicle-to-vehicle

communication protocol for cooperative collision warning," Proc. ofInternational Conference on Mobile and Ubiquitous Systems : Net­working and Services, pp. 114-123,2004.

[16] IEEE 1'1609.01D05, Trial Use Standards for Wireless Access inVehicular Environments(WAVE)-Architecture, February 2008.

[I7] IEEE 1609.1, Trial Usc Standards for Wireless Access in VehicularEnvironments(WAVE)-Resource Manager, 2006.

[I8] IEEE 1609.2, Trial Usc Standards for Wireless Access in VehicularEnvironments(WAVE)-Management Messages, 2006.

[19] IEEE 1609.3/DI.0, Trial Use Standards for Wireless Access in Vehic­ular Environments(WAVE)-Networking Services, December 2008.

[20] IEEE 1609.4/DI.0, Trial Use Standards for Wireless Access in Vehic­ular Environments(WAVE)-Multi-channel Operation, December 2008.

R EF ER ENC ES

power. Therefore, an appropriate design of antenna beampattern is also critical for implementation. Notice that theseimplementation issues are applicable to V2I communicationas well as V2V communication.

V. CONCLUSION REMARKS

In this paper, we introduced the anti-collision warningapplication by using V2V communication. Characteristics ofthe overall system are discussed with general and specialfeatures. We also described the detailed system specifica­tions, i.e., the communication platform, RF module/antennaand vehicle terminal. We verified that it is possible to sendand receive safety messages with SS and SA scenarios.Based on practical field tests, we also investigated someimplementation issues for safety applications, i.e., the preciselocation information , NLOS problem and antenna beampattern, in vehicular communications.

ETRI=-.=.-

VERY' EMERGENCY---------

warning message has to be delivered to user or not. Finally,the warning messages are notified by display and sound.

Fig. 6 depicts V2V service terminal. The vehicle terminaldisplays the information of my vehicle, front vehicle andrear vehicle. Depending on the received messages, warningor very warning messages are displayed. The vehicle terminalalso displays crash information to indicate an accident. Basedon practical field tests, we verifiy that it is possible to sendand receive a safety message appropriately from/to adjacentvehicles.

C. Implementation issues

In the previous subsection, we introduced the anti-collisionwarning application. Now let us consider several implemen­tation issues. Based on practical tests, it is revealed thatseveral problems have to be solved for reliable messagetransmission. First of all, the location information is criticalin vehicle safety application since the distance between thevehicles is based on the location. Although the performanceof communication, i.e., PER, link setup time and latency,is excellent, the anti-collision warning application cannotbe realized without the accurate location information. Weuse GPS to provide the vehicle location. It is ovserved thatlocation errors occur with GPS. To solve this problem, thetechnique for finding location with very high resolution hasto be developed. Another issue is non line-of-site (NLOS)problem. Since 5.9GHZ frequency band is used, it is hard toguarantee reliable communication link without LOS. How­ever, there are many curve areas in local roads and freeways,and some obstacles block the LOS path. We have to solvethis NLOS problem by building a relay node or using RSEas a simple signal relaying. The other problem is an antennabeam pattern. It is observed that communication links aredisconnected when vehicles are located very close. This isdue to the fact that the vertical beam width is too narrowto transmit signal to adjacent vehicles . To overcome thisphenomenon, the antenna beam pattern has to be designedfor transmitting and receiving signal between very closelylocated vehicles regardless of vehicle types. In addition ,the antenna provides enough gain to communicate withremote vehicles, i.e., up to lkm given the maximum transmit

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