Performance Evaluation of IEEE 802.11p

for Vehicular Communication 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 transportation

around the world

-Troubles and concerns have caused by increasing the number of

vehicles:

Growing the number of road accidents

Rising the cost in terms of victims and insured people

Increase in traffic congestion on the roads

Lack of parking space

Difficulty in predicting the speed of other vehicles and safety

distance

Wasting 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 mitigate

accident; however, they cannot eradicate problems completely.

-Intelligent Transportation System (ITS) is one of the information and

communication technologies which enhances transportation safety,

reliability, security and productivity by integrating with existing

technologies.

Introduction

-Wireless data communication between vehicles is one of the

technologies which has improved the deployment of ITS

applications.

-This communication is divided into two types:Vehicle to Vehicle (V2V): vehicles communicate directly with neighbour vehiclesVehicle to Infrastructure (V2I): two vehicles communicate indirectly by third party medium (e.g. roadside equipment)

-Vehicles are equipped with short-range wireless communication technology (approximately 100 to 300 meters)

-This is known as vehicular ad hoc network (VANET) technology.

Introduction

The major objectives of VANET:

Broadcast warning messages to neighbouring vehicles in case of car accidents, obstacle, bad weather conditions , and emergency braking on the road

Introduction

Obstacle on the road

 

Introduction

Emergency vehicle 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 the 802.11 standard in order to enhance the 802.11 to support VANETs.

-This standard is known as 802.11p, it defines physical and medium access control layers of VANETs.

-In addition, The IEEE 1609 working group defined IEEE 1609 protocol family which developed higher layer specification based on 802.11p.

-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 support multichannel operation

Research Focus-IEEE 1609 protocol family and 802.11p together are called WAVE standard. . This system architecture is used for automotive wireless communications .

-The contribution of this paper is to evaluate the IEEE 802.11p standard.

-A study was based on the structure of the WAVE architecture for VANETs.

-We, subsequently, set up one real scenario which assisted us in analysing the performance metrics of the IEEE 802.11p. This scenario was implemented and modelled using ns-2 network simulator with VanetMobiSim traffic simulator .

Related Work-One of the most important points in the vehicular network simulation is that the nature of vehicular communication is based on the movement. Therefore, it is necessary to implement a realistic vehicular movement in the simulation.

-Several publications [1], [2], [3] have studied the performance of 802.11p. However, none of the previous studies have supported realistic vehicular mobility simulation.

-In [4], the authors have presented a comprehensive evaluation and review of the performance of 802.11p and WAVE protocols supporting realistic vehicular mobility model. However, standards were implemented in Qualnet network simulator.

Related Work- In terms of modelling accuracy, a new model of IEEE 802.11 MAC and PHY, which support IEEE 802.11P, is designed and implemented in ns-2 network simulator version 2.34 [5]. This version of ns-2 network simulator is used in this paper.

- The main novelty of this paper is to implement the key parameters of 802.11p standard in ns-2, and prepare the realistic vehicular mobility model by VanetMobiSim

WAVE Architecture

WAVE Architecture

WAVE ArchitectureA- Physical and MAC Layers

-The physical and MAC layers of WAVE are based on IEEE 802.11p standard.

-The physical layer of IEEE 802.11p consists of seven channels in 5.9GHz band which uses 10MHZ bandwidth for each channel.

-The physical layer of 802.11p uses OFDM technology in order to increase data transmission rate and overcome signal fading in wireless communication.

-The management functions are connected to the physical and MAC layers called physical layer management entity (PLME) and MAC layer management entity (MLME), respectively.

-The IEEE 802.11p uses CSMA/CA to reduce collisions and provide fair access to the channel.

WAVE ArchitectureB- Multichannel Operation

-IEEE 1609.4 is one of the standards of the IEEE 1609 protocol family, which manages channel coordination and supports MAC service data unit delivery.

- This standard describes seven different channels with different features and usages (six service channels and one control channel). In addition, these channels use different frequencies and transmit powers.

-Each station continuously alternates between the control channel and one of the service channels.

-The control channel is used for system control and safety data transmission.

WAVE ArchitectureB- Multichannel Operation

- The IEEE 802.11p MAC layer is based on multichannel operation of WAVE architecture and 802.11e EDCA.

-EDCA mechanism defines four different access categories (AC) for each channel, and each of them has an independent queue.

- The EDCA mechanism provides prioritization by assigning different contention parameters to each access category.

-AC3 has the highest priority to access medium, whereas AC0 has the lowest priority.

-Each frame is categorized into different access categories, depending on the importance of the message.

WAVE ArchitectureB- Multichannel Operation

During data transmission, there are two contention procedures to access the medium: Internal contention procedure which occurs inside each channel between their access categories by using the contention parameters (AIFS and CW).

The contention procedure between channels to access the medium supported by different timer settings based on the internal contention procedure.

WAVE Architecture

B- Multichannel

Operation

The contention

procedure inside each

channel and

the channel coordination

WAVE ArchitectureC - Network and Transport Layers

-The IEEE 1609.3 defines the operation of services at network and transport layers. Moreover, it provides wireless connectivity between vehicles, and vehicles to roadside devices.

-The functions of the WAVE network services can be separated into two sets:Data-plane services: They transmit network traffics and support IPV6 and WAVE short-message- Protocol (WSMP) protocols.

Management-plane services: Their functions are to configure and maintain system, for instance: IPV6 configuration, channel usage monitoring, and application registration. This service is known as WAVE management entity (WME).

WAVE ArchitectureD - Resource Manager

IEEE 1609.1 standard defines a WAVE application known as resource manager (RM) which allows communication between applications runs on Roadside units (RSU) and On-board units (OBU).

E - Security Services

- The IEEE 1609.2 standard defines security services for the WAVE architecture and the applications which run through this architecture.

- This standard defines the format and the processing of secure messages.

SimulationSimulation in VANET consists of two components: Traffic simulation : generates a trace file which provides realistic vehicles movement. This trace file is fed into the network simulator which defines the realistic position of each vehicle during the network simulationNetwork simulation: The network simulator then implements the VANET protocols and produces a trace file which prepares complete information about the events taking place in the scenario. Information is then analysed to evaluate the performance metrics of the IEEE 802.11p in VANET.

Simulation- VanetMobiSim is selected as a traffic simulator for this paper. This simulator supports Intelligent DriverModel with Intersection Management (IDMIM) which generates realistic vehicular mobility model .

-Vehicular safety communications based on IEEE 802.11p consist of safety broadcast messages between neighbouring vehicles. Consequently, the overall IEEE 802.11p performance is related to broadcast messages reception performance.

-PBC agent is a broadcast message generator implemented in ns-2 version 2.34. We used this agent in order to define the broadcast message generation behaviour in our simulation.

Simulation-The scenario is a highway of 1500 metres long with three lanes in one direction and nine vehicles moving in these three lanes.

-The maximum speeds of the lanes are around 80, 100 and 130 km/h respectively. 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 situation travelling in the same direction as other vehicles at the speed of 150 km/h. The ambulance is located behind other cars which are 100 metres apart.

- The ambulance transmits one periodic broadcast message with a payload of 250 bytes in every 0.2 seconds.

Simulation- In order to evaluate the effect of different message sizes on the performance metrics, we implemented another two scenarios in which the ambulance transmits period broadcast messages with the payload of 500, 1000 bytes respectively.

-Each network simulations run twenty times with the same mobility trace to obtain an average and get a notion of statistical significance.- simulation run-time 65 seconds.

Results

0102030405060708090

100110120130140150160170

0 6 12 18 24 30 36 42 48 54 60

Dis

tanc

e (m

)

Simulation Time (s)Vehicle 2

Vehicle 4

Vehicle 10 Distance between the ambulance and other vehicles during movement

Results

Packet loss between the ambulance and other vehicles during movement

Packet loss (%)

Simulation Time (s)

▬Packet loss between vehicle 1 and 2▬Packet loss between vehicle 1 and 4▬Packet loss between vehicle 1 and 10

Results-There is no packet loss between the ambulance and vehicle 4 after 58 seconds of the simulation time, and the distance between the ambulance and vehicle 4 is less than 138 metres after 58 seconds.

-Packet loss is dropped to 0% after 38 seconds of simulation, at the same time the distance between ambulance and vehicle 10 is less than 138 metres after 38 seconds.

-It provides similar results for vehicle 10 and 4. Accordingly, the vehicles can receive the broadcast message when their distance from the ambulance is less than 138 metres.

Results

Throughput of vehicle 2,4, and 10 (message size 250 bytes)

-0.1

0.4

0.9

1.4

1.9

2.4

2.9

3.4

3.9

4.4

4.9

5.4

5.9

6.4

0 10 20 30 40 50 60

Thro

ughp

ut (k

bp

s)

Simualtion Time (s)

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 less than 138 metres.

- All of the vehicles have nearly similar throughput when the distances 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 the varying speed.

Results

End-to-End delay between the ambulance and other vehicles (message size 250 bytes)

0.466

0.46605

0.4661

0.46615

0.4662

0.46625

0.4663

0.46635

0.4664

0.46645

0.4665

0 5 10 15 20 25 30 35 40 45 50 55 60 65

En

d-t

o-E

nd

Del

ay (

ms)

Simulation Time (s)End-to-End Delay between vehicle 1 and 2

End-to-End Delay between vehicle 1 and 4

End-to-End Delay Between vehicle 1 and 10

0102030405060708090

100110120130140150160170

0 6 12 18 24 30 36 42 48 54 60

Dis

tan

ce (

m)

Simulation Time (s)Vehicle 2

Vehicle 4

Vehicle 10

Distance between the ambulance and other vehicles during movement

Results-A comparison between two figures shows that as long as the distance between vehicle and the ambulance is below 138 metres, the results 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 the distance between sender and receiver of the message.

- As mentioned earlier, vehicles have different speed; consequently, various vehicle speeds do not have any impact on End-to-End delay.

Results

Average throughput of vehicles (message size 250 bytes)

0

0.3

0.6

0.9

1.2

1.5

1.8

2 3 4 5 6 7 8 9 10

Av

erag

e T

hrou

ghpu

t (kb

ps)

Vehicle Numbers

Average distance between the ambulance and other vehicles (message size 250 bytes)

Average packet loss between the ambulance and other vehicles (message size of 250 bytes)

0

20

40

60

80

100

120

140

160

180

2 3 4 5 6 7 8 9 10

Av

erag

e D

ista

nce

(m

)

Vehicle Numbers

0

10

20

30

40

50

60

70

80

90

100

2 3 4 5 6 7 8 9 10

Av

erag

e P

ack

age

Los

s (%

)

Vehicle Numbers

Results-The probability of message reception for vehicles 4, 7 and 10 is less than other vehicles and they have the highest average packet loss, since their average distance is more than other vehicles and at the beginning of simulation their distance from the ambulance is more than 138 metres.

- However other vehicles, which their distances do not exceed 138 metres from the ambulance during simulation time, have equal and highest rate of average throughout without any packet loss.

-This is another reason indicating that throughput and packet loss are not influenced by different vehicle speed.

Results

Average throughput of vehicles with different message sizes

Average End-to-End delay between the ambulance and other vehicles with different message size

0123456789

10

0 1 2 3 4 5 6 7 8 9 10

Av

erag

e T

hro

ugh

pu

t (k

bps

)

Vehicle NumbersMessage size 250 bytes

Message size 500 bytes

Message size 1000 bytes

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 1 2 3 4 5 6 7 8 9 10

Av

erag

e E

nd-t

oEn

d D

elay

(ms)

Vehicle NumbersMessage size 250 bytes

Message size 500 bytes

Message size 1000 bytes

- 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 performance metrics (throughput, End-to-End delay, and packet loss) are not affected by varying vehicle speed.

-Analysis of throughput for the all vehicles showed that the probability of successful message reception was same for all the vehicles when the distance between sender and receiver of the message was less than 138 metres.

- In addition, End-to-end delay metric was directly related to the distance between the vehicle transmitting the broadcast messages and its neighbouring vehicles.

-Results of scenarios with different message sizes demonstrated that the average throughput and End-to-End delay metrics were increased by increasing message sizes.

References[1] S. Eichler, “Performance evaluation of the IEEE 802.11p WAVE communication standard,” in Proc. IEEE Vehicular Technology Conf., Baltimore, MD, US, Oct. 2007, pp. 2199-2203.

[2] T. Murray, M. Cojocari, H. Fu, “Measuring the performance of IEEE 802.11p using ns-2 simulator for vehicular networks,” in: Proc. IEEE EIT, 2008, pp. 98–503.

[3] K. Bilstrup, E. Uhlemann, E. G. Ström and U. Bilstrup, “Evaluation of the IEEE 802.11p MAC method for vehicle-to-vehicle communication,” Proc. IEEE Int. Symposium on Wireless Vehicular Communications, Calgary, Canada, Sept. 2008.

[4] S. Grafling, P. Mahonen, and J. Riihijarvi, “Performance evaluation of IEEE 1609 WAVE and IEEE 802.11p for vehicular communications,” in Proceedings of the 2nd International Conference on Ubiquitous and Future Networks (ICUFN ’10), June 2010, pp. 344 –348.

[5] Q. Chen, F. Schmidt-Eisenlohr, D. Jiang, M. Torrent-Moreno, L. Delgrossi, and H. Hartenstein, “Overhaul of IEEE 802.11 modeling and simulation in ns-2,” in Proc. 10th ACM Symp. MSWiM, Chania, Greece, Oct. 2007, pp. 159–168.