Performance Evaluation Of IEEE 802.11p For Vehicular Communication Networks
Performance Evaluation ofIEEE 802.11p for VehicularCommunication Networks A. Jafari, S. Al-Khayatt and A. Dogman Faculty of Art, Computing, Engineering and Sciences, Sheffield Hallam University, Sheffield, United Kingdom
Introduction-Vehicles are definitely the most popular means of transportationaround the world-Troubles and concerns have caused by increasing the number ofvehicles:Growing the number of road accidentsRising the cost in terms of victims and insured peopleIncrease in traffic congestion on the roadsLack of parking spaceDifficulty in predicting the speed of other vehicles and safetydistanceWasting millions of hours and energy by vehicles every day
Introduction-Current safety technology systems (e.g. airbag, seatbelts, ABS, EPS)support drivers and passengers in critical condition to avoid or mitigateaccident; however, they cannot eradicate problems completely.-Intelligent Transportation System (ITS) is one of the information andcommunication technologies which enhances transportationsafety, reliability, security and productivity by integrating withexisting technologies.
Introduction-Wireless data communication between vehicles is one of thetechnologies which has improved the deployment of ITSapplications.-This communication is divided into two types:Vehicle to Vehicle (V2V): vehicles communicate directly withneighbour vehiclesVehicle to Infrastructure (V2I): two vehicles communicate indirectly bythird party medium (e.g. roadside equipment)-Vehicles are equipped with short-range wireless communicationtechnology (approximately 100 to 300 meters)-This is known as vehicular ad hoc network (VANET) technology.
IntroductionThe major objectives of VANET:Broadcast warning messages to neighbouring vehicles in case ofcar accidents, obstacle, bad weather conditions , and emergencybraking on the road
IntroductionProvide drivers with latest real-time traffic informationHelp emergency vehicles to pass other vehicles quicklyAssist drivers to find accessible parking spaceSupply automobile internet accessReceive online mechanic help when the car breaks down
Research Focus-In 2004, IEEE 802.11 task group p developed an amendment to the802.11 standard in order to enhance the 802.11 to support VANETs.-This standard is known as 802.11p, it defines physical and mediumaccess control layers of VANETs.-In addition, The IEEE 1609 working group defined IEEE 1609protocol family which developed higher layer specification based on802.11p.-This protocol consists of four documents:IEEE 1609.1: describes resource manager specificationIEEE 1609.2: defines the formats and processing of secure messagesIEEE 1609.3: covers network and transport layer servicesIEEE 1609.4: specifies improvement to the IEEE 802.11p MAC to supportmultichannel operation
Research Focus-IEEE 1609 protocol family and 802.11p together are called WAVEstandard. . This system architecture is used for automotive wirelesscommunications .-The contribution of this paper is to evaluate the IEEE 802.11pstandard.-A study was based on the structure of the WAVE architecture forVANETs.-We, subsequently, set up one real scenario which assisted us inanalysing the performance metrics of the IEEE 802.11p. Thisscenario was implemented and modelled using ns-2 networksimulator with VanetMobiSim traffic simulator .
Related Work-One of the most important points in the vehicular network simulationis that the nature of vehicular communication is based on themovement. Therefore, it is necessary to implement a realisticvehicular movement in the simulation.-Several publications , ,  have studied the performance of802.11p. However, none of the previous studies have supportedrealistic vehicular mobility simulation.-In , the authors have presented a comprehensive evaluation andreview of the performance of 802.11p and WAVE protocols supportingrealistic vehicular mobility model. However, standards wereimplemented in Qualnet network simulator.
Related Work- In terms of modelling accuracy, a new model of IEEE 802.11 MACand PHY, which support IEEE 802.11P, is designed and implementedin ns-2 network simulator version 2.34 . This version of ns-2network simulator is used in this paper.- The main novelty of this paper is to implement the key parametersof 802.11p standard in ns-2, and prepare the realistic vehicularmobility model by VanetMobiSim
WAVE ArchitectureA- Physical and MAC Layers-The physical and MAC layers of WAVE are based on IEEE 802.11pstandard.-The physical layer of IEEE 802.11p consists of seven channels in5.9GHz band which uses 10MHZ bandwidth for each channel.-The physical layer of 802.11p uses OFDM technology in order toincrease data transmission rate and overcome signal fading in wirelesscommunication.-The management functions are connected to the physical and MAClayers called physical layer management entity (PLME) and MAC layermanagement entity (MLME), respectively.-The IEEE 802.11p uses CSMA/CA to reduce collisions and provide fairaccess to the channel.
WAVE ArchitectureB- Multichannel Operation-IEEE 1609.4 is one of the standards of the IEEE 1609 protocolfamily, which manages channel coordination and supports MACservice data unit delivery.- This standard describes seven different channels with differentfeatures and usages (six service channels and one controlchannel). In addition, these channels use different frequencies andtransmit powers.-Each station continuously alternates between the control channeland one of the service channels.-The control channel is used for system control and safety datatransmission.
WAVE ArchitectureB- Multichannel Operation- The IEEE 802.11p MAC layer is based on multichannel operationof WAVE architecture and 802.11e EDCA.-EDCA mechanism defines four different access categories (AC) foreach channel, and each of them has an independent queue.- The EDCA mechanism provides prioritization by assigning differentcontention parameters to each access category.-AC3 has the highest priority to access medium, whereas AC0 has thelowest priority.-Each frame is categorized into different access categories, dependingon the importance of the message.
WAVE ArchitectureB- Multichannel OperationDuring data transmission, there are two contention procedures toaccess the medium:Internal contention procedure which occurs inside each channelbetween their access categories by using the contention parameters(AIFS and CW).The contention procedure between channels to access the mediumsupported by different timer settings based on the internal contentionprocedure.
WAVEArchitectureB- MultichannelOperationThe contentionprocedure inside each channel andthe channel coordination
WAVE ArchitectureC - Network and Transport Layers-The IEEE 1609.3 defines the operation of services at network andtransport layers. Moreover, it provides wireless connectivity betweenvehicles, and vehicles to roadside devices. -The functions of the WAVE network services can be separated intotwo sets:Data-plane services: They transmit network traffics and supportIPV6 and WAVE short-message- Protocol (WSMP) protocols.Management-plane services: Their functions are to configure andmaintain system, for instance: IPV6 configuration, channel usagemonitoring, and application registration. This service is known asWAVE management entity (WME).
WAVE ArchitectureD - Resource ManagerIEEE 1609.1 standard defines a WAVE application known as resourcemanager (RM) which allows communication between applicationsruns on Roadside units (RSU) and On-board units (OBU).E - Security Services- The IEEE 1609.2 standard defines security services for the WAVEarchitecture and the applications which run through this architecture.- This standard defines the format and the processing of securemessages.
SimulationSimulation in VANET consists of two components: Traffic simulation : generates a trace file which provides realisticvehicles movement. This trace file is fed into the network simulatorwhich defines the realistic position of each vehicle during the networksimulationNetwork simulation: The network simulator then implements theVANET protocols and produces a trace file which prepares completeinformation about the events taking place in the scenario. Informationis then analysed to evaluate the performance metrics of the IEEE802.11p in VANET.
Simulation- VanetMobiSim is selected as a traffic simulator for this paper. Thissimulator supports Intelligent DriverModel with IntersectionManagement (IDMIM) which generates realistic vehicular mobilitymodel .-Vehicular safety communications based on IEEE 802.11p consist ofsafety broadcast messages between neighbouring vehicles.Consequently, the overall IEEE 802.11p performance is related tobroadcast messages reception performance.-PBC agent is a broadcast message generator implemented in ns-2version 2.34. We used this agent in order to define the broadcastmessage generation behaviour in our simulation.
Simulation-The scenario is a highway of 1500 metres long with three lanes inone direction and nine vehicles moving in these three lanes.-The maximum speeds of the lanes are around 80, 100 and 130 km/hrespectively. The speed limit for each lane is 60 km/h.- The distance between each lane is 4 metres.- In the scenario, an ambulance is in the emergency situationtravelling in the same direction as other vehicles at the speed of 150km/h. The ambulance is located behind other cars which are 100metres apart.- The ambulance transmits one periodic broadcast message with apayload of 250 bytes in every 0.2 seconds.
Simulation- In order to evaluate the effect of different message sizes on theperformance metrics, we implemented another two scenarios in whichthe ambulance transmits period broadcast messages with the payloadof 500, 1000 bytes respectively.-Each network simulations run twenty times with the same mobilitytrace to obtain an average and get a notion of statisticalsignificance.- simulation run-time 65 seconds.
Results 170 160 150 140 130 120 Distance (m) 110 100 90 80 70 60 50 40 30 20 10 0 0 6 12 18 24 30 36 42 48 54 60 Vehicle 2 Simulation Time (s) Vehicle 4 Vehicle 10 Distance between the ambulance and other vehicles during movement
Results Packet loss (%) Packet loss between vehicle 1 and 2 Packet loss between vehicle 1 and 4 Simulation Time (s) Packet loss between vehicle 1 and 10 Packet loss between the ambulance and other vehicles during movement
Results-There is no packet loss between the ambulance and vehicle 4 after58 seconds of the simulation time, and the distance between theambulance and vehicle 4 is less than 138 metres after 58 seconds.-Packet loss is dropped to 0% after 38 seconds of simulation, at thesame time the distance between ambulance and vehicle 10 is lessthan 138 metres after 38 seconds.-It provides similar results for vehicle 10 and 4. Accordingly, thevehicles can receive the broadcast message when their distancefrom the ambulance is less than 138 metres.
Results 6.4 5.9 5.4 4.9 Throughput (kbps) 4.4 3.9 3.4 2.9 2.4 1.9 1.4 0.9 0.4 -0.1 0 10 20 30 40 50 60 Simualtion Time (s) Throughput of vehicle 2,4, and 10 (message size 250 bytes)
Results-Throughput of vehicles 4 and 10 fluctuate between 1.8 and 2.2 Kbps,when the distances between the vehicles and the ambulance are lessthan 138 metres.- All of the vehicles have nearly similar throughput when thedistances between vehicles and ambulance are less than 138 metres.- The most important point is that each vehicle has different speed,as a result the throughput and packet loss are not affected by thevarying speed.
Results 0.4665 0.46645 170 0.4664 160 150End-to-End Delay (ms) 140 0.46635 130 120 Distance (m) 0.4663 110 100 0.46625 90 80 0.4662 70 60 0.46615 50 40 0.4661 30 20 10 0.46605 0 0.466 0 6 12 18 24 30 36 42 48 54 60 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Vehicle 2 Simulation Time (s) End-to-End Delay between vehicle 1 and 2 Simulation Time (s) Vehicle 4 End-to-End Delay between vehicle 1 and 4 Vehicle 10 End-to-End Delay Between vehicle 1 and 10 End-to-End delay between the Distance between the ambulance and ambulance and other vehicles other vehicles during movement (message size 250 bytes)
Results-A comparison between two figures shows that as long as thedistance between vehicle and the ambulance is below 138 metres, theresults of both figures look similar.-As the distance between sender and receiver increases, End-to-End delay increases accordingly.-It is observed that End-to-End delay is significantly influenced by thedistance between sender and receiver of the message.- As mentioned earlier, vehicles have different speed;consequently, various vehicle speeds do not have any impact onEnd-to-End delay.
Results 180 1.8 160 Average Throughput (kbps) Average Distance (m) 140 1.5 120 1.2 100 0.9 80 60 0.6 40 0.3 20 0 0 2 3 4 5 6 7 8 9 10 2 3 4 5 6 7 8 9 10 Vehicle Numbers Vehicle NumbersAverage throughput of Average distance between thevehicles 100 ambulance and other vehicles(message size 250 bytes) 90 (message size 250 bytes) 80 Package Loss (%) 70 60 Average 50 40 30 20 10 0 2 3 4 5 6 7 8 9 10 Vehicle Numbers Average packet loss between the ambulance and other vehicles (message size of 250 bytes)
Results-The probability of message reception for vehicles 4, 7 and 10 isless than other vehicles and they have the highest average packetloss, since their average distance is more than other vehicles and atthe beginning of simulation their distance from the ambulance ismore than 138 metres.- However other vehicles, which their distances do not exceed 138metres from the ambulance during simulation time, have equal andhighest rate of average throughout without any packet loss.-This is another reason indicating that throughput and packet lossare not influenced by different vehicle speed.
Results 1.6 10 Average End-toEnd Delay (ms)Average Throughput (kbps) 9 1.4 8 1.2 7 1 6 5 0.8 4 0.6 3 2 0.4 1 0.2 0 0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 Message size 250 bytes Vehicle Numbers Message size 250 bytes Vehicle Numbers Message size 500 bytes Message size 500 bytes Message size 1000 bytes Message size 1000 bytes Average throughput of vehicles with different Average End-to-End delay between the message sizes ambulance and other vehicles with different message size - According to these figures the average throughput and End-to-End delay are increased by increasing the message size, but the increment of throughput of vehicles 4, 7, and 10 is not as high as other vehicles.
Conclusion- Based on our findings, we have observed that the performancemetrics (throughput, End-to-End delay, and packet loss) are notaffected by varying vehicle speed.-Analysis of throughput for the all vehicles showed that theprobability of successful message reception was same for all thevehicles when the distance between sender and receiver of themessage was less than 138 metres.- In addition, End-to-end delay metric was directly related to thedistance between the vehicle transmitting the broadcast messagesand its neighbouring vehicles.-Results of scenarios with different message sizes demonstrated thatthe average throughput and End-to-End delay metrics wereincreased by increasing message sizes.
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