1. 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
Email: Amir.Jafari@student.shu.ac.uk; s.alkhayatt@shu.ac.uk; aadogman@my.shu.ac.uk
Abstract— IEEE 802.11p is an emerging standard which vehicles. Due to the characteristics of VANET and limited
provides vehicular safety communication through wireless bandwidth, periodic broadcast messages can consume the
networks. In this paper, the architecture of Wireless Access entire available bandwidth. Furthermore; the emergency
for Vehicular Environment (WAVE) and IEEE 802.11p messages need to be disseminated quickly and efficiently.
standard were analysed. The key parameters of this Consequently, there is a need to prioritise important and
standard are implemented in ns-2 network simulator to time-critical messages and use quality of services. The
accurately simulate vehicular ad hoc networks (VANETs). IEEE 802.11p MAC layer implements a priority scheme
The performance of this standard was measured in ns-2 in a similar way to IEEE 802.11e EDCA function.
network simulation environment using realistic vehicular
The contribution of this paper is to evaluate the IEEE
mobility models. The main performance metrics for
802.11p standard. A study was based on the structure of
vehicular safety communication; Throughput, End-to-End
the WAVE architecture for VANETs. We, subsequently,
delay, and Packet loss ratio were analysed for our scenario.
set up one real scenario which assisted us in analysing the
In addition, the effect of varying vehicle speed and different
message sizes on the performance metrics were measured.
performance metrics of the IEEE 802.11p. This scenario
was implemented and modelled using ns-2 network
I. INTRODUCTION simulator [2] with VanetMobiSim traffic simulator [3].
One of the most important points in the vehicular network
Intelligent Transportation System (ITS) is one of the simulation was that the nature of vehicular communication
information and communication technologies which has is based on the movement. Therefore, it is necessary to
attracted a lot of attention recently. This technology implement a realistic vehicular movement in the
enhances transportation safety, reliability, security and simulation. The main novelty of this paper is to implement
productivity by integrating with existing technologies. the key parameters of 802.11p standard in ns-2, and
Wireless data communication between vehicles is one of prepare the realistic vehicular mobility model by
the technologies which has improved the deployment of VanetMobiSim. In other words, all of the important
ITS applications. This communication is divided into two parameters are implemented accurately in the VANET
types: Vehicle to Vehicle (V2V) and Vehicle to simulation.
Infrastructure (V2I). Vehicles are equipped with short
range wireless communication technology (approximately Several publications [4], [5], [6] have studied the
100 to 300 metres) acting as computer nodes on the road. performance of 802.11p. However, none of the previous
This is known as vehicular ad hoc network (VANET) studies have supported realistic vehicular mobility
technology. The major objectives of VANET technology simulation. In [7], the authors have presented a
can be stated as follows: broadcasts warning messages to comprehensive evaluation and review of the performance
neighbouring vehicles in case of car accidents help of 802.11p and WAVE protocols supporting realistic
emergency vehicles to pass other vehicles quickly, and vehicular mobility model. However, standards were
provides drivers with latest real-time traffic information. implemented in Qualnet network simulator. In terms of
modelling accuracy, a new model of IEEE 802.11 MAC
A wide range of project activities have initiated around and PHY, which support IEEE 802.11P, is designed and
the world in order to improve vehicular communication implemented in ns-2 network simulator version 2.34 [8].
networks. In 2004, IEEE 802.11 task group p developed This version of ns-2 network simulator is used in this
an amendment to the 802.11 standard in order to enhance paper.
the 802.11 to support VANETs. This standard is known as
802.11p, it defines physical and medium access control The remainder of this paper is organised as follows. In
layers of VANETs. In addition, The IEEE 1609 working section II the WAVE and IEEE802.11p structure are
group defined IEEE 1609 protocol family which clarified. The simulation scenario is conducted in section
developed higher layer specification based on 802.11p. III. Results from the simulation and the analyses of the
This protocol consists of four documents: IEEE 1609.1, performance metrics of the IEEE 802.11p are presented in
IEEE 1609.2, IEEE 1609.3, and IEEE 1609.4. IEEE 1609 section IV. Finally, this paper is concluded in Section V.
protocol family and 802.11p together are called WAVE II. VEHICULAR COMMUNICATION BASED ON THE
standard. This system architecture is used for automotive
IEEE 802.11P AND WAVE SYSTEM
wireless communications [1].
The specific nature of VANET makes it different from In this section we briefly present an outline of WAVE
other kinds of networks; some of the characteristics of architecture system and IEEE 802.11p protocol for
VANET are high mobility, short communication periods, VANET.
dynamic topology and limited bandwidth. Communication
in VANETs is based on event-driven messages or
broadcast messages exchanged between surrounding
2. A. Physical and MAC Layers The contention procedure between channels to
The physical and MAC layers of WAVE are based on access the medium supported by different timer
IEEE 802.11p standard. The physical layer of IEEE settings based on the internal contention
802.11p consists of seven channels in 5.9GHz band which procedure. [7]
is similar to IEEE 802.11a design, but the main difference Logical link control (LLC) is another element of
is that the IEEE 802.11p uses 10MHZ bandwidth for each WAVE structure which is similar to upper sub-layer of
channel instead of 20MHZ bandwidth in IEEE 802.11a. OSI layer two. LLC provides the communication between
The physical layer of 802.11p uses OFDM technology in upper layers and the lower layer.
order to increase data transmission rate and overcome
signal fading in wireless communication. One of the C. Network and Transport Layers
specifications of IEEE 802.11p is that the management The IEEE 1609.3 defines the operation of services at
functions are connected to the physical and MAC layers network and transport layers. Moreover, it provides
called physical layer management entity (PLME) and wireless connectivity between vehicles, and vehicles to
MAC layer management entity (MLME), respectively [4]. roadside devices. The functions of the WAVE network
The IEEE 802.11p uses CSMA/CA to reduce collisions services can be separated into two sets:
and provide fair access to the channel. Data-plane services: They transmit network
traffics and support IPV6 and WSMP protocols.
Resource Manager Security WAVE short-message- Protocol (WSMP)
IEEE 1609.1 Services provides this capability that applications can send
UDP/TCP WSMP IEEE
IPV6 WME 1609.2 short message to increase the probability of
LLC IEEE receiving the messages in time.
Multi Channel Operation 1609.3 Management-plane services: Their functions are
IEEE 1609.4 to configure and maintain system, for instance:
WAVE MAC MLME IPV6 configuration, channel usage monitoring,
IEEE 802.11p and application registration. This service is
WAVE PHY PLME
IEEE 802.11p
known as WAVE management entity (WME).
Figure 1. WAVE Architecture D. Resource Manager
B. Multichannel Operation IEEE 1609.1 standard defines a WAVE application
known as resource manager (RM) which allows
IEEE 1609.4 is one of the standards of the IEEE 1609 communication between applications runs on Roadside
protocol family, which manages channel coordination and units (RSU) and On-board units (OBU). The RM resides
supports MAC service data unit delivery. This standard on either OBUs or RSUs [10].
describes seven different channels with different features
and usages (six service channels and one control channel). E. Security Services
In addition, these channels use different frequencies and The IEEE 1609.2 standard defines security services for
transmit powers. Eichler [4] mentions that each station the WAVE architecture and the applications which run
continuously alternates between the control channel and
one of the service channels; however the different through this architecture. This standard defines the format
channels cannot be used at the same time. According to and the processing of secure messages [1].
[9], the control channel is used for system control and
safety data transmission. III. SIMULATION
The IEEE 802.11p MAC layer is based on multichannel Implementing and deploying VANETs in a real world
operation of WAVE architecture and 802.11e EDCA. can be prohibitively expensive and difficult.
EDCA mechanism defines four different access categories Consequently, most of the researches in the area of
(AC) for each channel. The access categories are indicated Vehicular communication network are based on
by AC0-AC3, and each of them has an independent queue simulation for evaluation [11].
[4]. The EDCA mechanism provides prioritization by Simulation in VANET consists of two components:
assigning different contention parameters to each access traffic simulation and network simulation. Traffic
category. AC3 has the highest priority to access medium, simulation focuses on vehicular mobility and it generates
whereas AC0 has the lowest priority. Each frame is a trace file which provides realistic vehicles movement.
categorized into different access categories, depending on This trace file is fed into the network simulator which
the importance of the message. In IEEE 802.11p MAC defines the realistic position of each vehicle during the
layer, there are six service channels and one control network simulation. The network simulator then
channel and each of them has four different access implements the VANET protocols and produces a trace
categories. Consequently, during data transmission, there file which prepares complete information about the events
are two contention procedures to access the medium: taking place in the scenario. Information is then analysed
Internal contention procedure which occurs to evaluate the performance metrics of the IEEE 802.11p
inside each channel between their access in VANET.
categories by using the contention parameters VanetMobiSim is selected as a traffic simulator for this
(Arbitrary InterFrame space (AIFS) and paper, since it is an open source and is validated against
Contention Window (CW)). commercial simulators. This simulator supports Intelligent
DriverModel with Intersection Management (IDMIM)
which generates realistic vehicular mobility model [12].
3. Jiang et al. [13] mention that vehicular safety 170
communications based on IEEE 802.11p consist of safety 160
150
broadcast messages between neighbouring vehicles. 140
130
Consequently, the overall IEEE 802.11p performance is 120
Distance (m)
110
related to broadcast messages reception performance. PBC 100
90
agent is a broadcast message generator implemented in ns- 80
70
2 version 2.34. We used this agent in order to define the 60
50
broadcast message generation behaviour in our simulation. 40
30
20
The scenario is a highway of 1500 metres long with three 10
0
lanes in one direction and nine vehicles moving in these
0 6 12 18 24 30 36 42 48 54 60
three lanes. The maximum speeds of the lanes are around
Vehicle 2
80, 100 and 130 km/h respectively. The speed limit for Simulation Time (s)
Vehicle 4
each lane is 60 km/h. The distance between each lane is 4
metres. In the scenario, an ambulance is in the emergency Vehicle 10
situation travelling in the same direction as other vehicles Figure 3. Distance between the ambulance and other vehicles during
at the speed of 150 km/h. The ambulance is located behind movement
other cars which are 100 metres apart. The IDMIM
generates realistic vehicular mobility model. The Packet loss (%)
ambulance transmits one periodic broadcast message with
a payload of 250 bytes in every 0.2 seconds. 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.
▬Packet loss between vehicle 1 and 2
▬Packet loss between vehicle 1 and 4 Simulation Time (s)
▬Packet loss between vehicle 1 and 10
Figure 4. Packet loss between the ambulance and other vehicles during
movement
Figure 2. Scenario
IV. RESULTS Fig. 5 demonstrates the throughput of vehicles 2, 4, and
10 with the message size of 250 bytes. The figure shows
Results obtained from the scenario previously described that the throughput of vehicles 4 and 10 fluctuate between
are presented in this section. Throughput, End-to-End 1.8 and 2.2 Kbps, when the distances between the vehicles
delay, and packet loss were calculated for nine vehicles as and the ambulance are less than 138 metres. It can be seen
numbered in Fig. 2 during the simulation run-time (i.e. 65 from Fig. 5 that all of the vehicles have nearly similar
seconds). In addition, the impact of various speeds on throughput when the distances between vehicles and
different performance metrics was also evaluated. ambulance are less than 138 metres. In other words,
Fig. 3 shows the distances between the ambulance and throughput of all the vehicles which their distances do not
vehicles 2, 4, and 10 throughout the simulation . Also, exceed 138 metres from the ambulance are same and there
Packet loss between the ambulance and these vehicles is no packet loss between these vehicles and ambulance.
during the simulation time is illustrated in Fig. 4. It is The most important point is that each vehicle has different
clearly shown in Fig. 4 that there is no packet loss speed, as a result the throughput and packet loss are not
between the ambulance and vehicle 4 after 58 seconds of affected by the varying speed.
the simulation time; regarding to Fig. 3, the distance
6.4
between the ambulance and vehicle 4 is less than 138 5.9
metres after 58 seconds. Fig.4 shows that packet loss is 5.4
dropped to 0% after 38 seconds of simulation, at the same 4.9
Throughput (kbps)
time Fig. 3 demonstrates that the distance between 4.4
3.9
ambulance and vehicle 10 is less than 138 metres after 38 3.4
seconds. It provides similar results for vehicle 10 and 4. 2.9
Accordingly, the vehicles can receive the broadcast 2.4
1.9
message when their distance from the ambulance is less 1.4
than 138 metres. 0.9
0.4
-0.1
0
0 10 20 30 40 50 60
Simualtion Time (s)
Figure 5. Throughput of vehicle 2,4, and 10 (message size 250 bytes)
4. 180
End-to-End delay between the ambulance and vehicles 160
2, 4, and 10 with the message size of 250 bytes are shown
Average Distance (m)
140
in Fig. 6. A comparison between Fig. 3 and Fig. 6 shows 120
that as long as the distance between vehicle and the 100
ambulance is below 138 metres, the results of both figures 80
look similar. As the distance between sender and receiver 60
40
increases, End-to-End delay increases accordingly. It is
20
observed that End-to-End delay is significantly influenced 0
by the distance between sender and receiver of the 2 3 4 5 6 7 8 9 10
message. As mentioned earlier, vehicles have different Vehicle Numbers
speed; consequently, various vehicle speeds do not have
any impact on End-to-End delay. Figure 8. Average distance between the ambulance and other vehicles
(message size 250 bytes)
0.4665
100
0.46645
90
0.4664 80
End-to-End Delay (ms)
Package Loss (%)
0.46635 70
60
Average
0.4663
50
0.46625
40
0.4662 30
0.46615 20
10
0.4661
0
0.46605
2 3 4 5 6 7 8 9 10
0.466 Vehicle Numbers
0 5 10 15 20 25 30 35 40 45 50 55 60 65
End-to-End Delay between vehicle 1 and 2
Simulation Time (s)
Figure 9. Average packet loss between the ambulance and other
End-to-End Delay between vehicle 1 and 4
vehicles (message size of 250 bytes)
End-to-End Delay Between vehicle 1 and 10
Fig. 10 and Fig. 11 illustrate the average throughput and
End-to-End delay with three different message sizes (250,
Figure 6. End-to-End delay between the ambulance and other vehicles 500, 1000 bytes). According to these figures the average
(message size 250 bytes) throughput and End-to-End delay are increased by
increasing the message size, but the increment of
Fig. 7, Fig. 8 and Fig. 9 illustrate the average throughput of vehicles 4, 7, and 10 is not as high as other
throughput, distance and packet loss between all vehicles vehicles.
and the ambulance respectively. The probability of
message reception for vehicles 4, 7 and 10 is less than 10
other vehicles and they have the highest average packet
Average Throughput (kbps)
9
8
loss, since their average distance is more than other 7
vehicles and at the beginning of simulation their distance 6
5
from the ambulance is more than 138 metres. However 4
other vehicles, which their distances do not exceed 138 3
metres from the ambulance during simulation time, have 2
1
equal and highest rate of average throughout without any 0
packet loss. This is another reason indicating that 0 1 2 3 4 5 6 7 8 9 10
throughput and packet loss are not influenced by different Message size 250 bytes
Vehicle Numbers
vehicle speed. Message size 500 bytes
Message size 1000 bytes
1.8
Average Throughput (kbps)
Figure 10. Average throughput of vehicles with different message sizes
1.5
1.2
0.9
0.6
0.3
0
2 3 4 5 6 7 8 9 10
Vehicle Numbers
Figure 7. Average throughput of vehicles (message size 250 bytes)
5. [9] M. Amadeo, C. Campolo, and A. Molinaro, "Enhancing IEEE
1.6 802.11p/WAVE to provide infotainment applications in
Average End-toEnd Delay (ms)
1.4 VANETs," Ad Hoc Networks, Elsevier, 2010.
1.2 [10] WILLIAMS, B. “Intelligent Transport Systems Standards,” Artech
1 House Publishers, 2008.
0.8 [11] S. Olariu and M. Weigle, Eds., “Vehicular Networks: From
0.6 Theory to Practice,” Chapman & Hall/CRC, 2009.
0.4 [12] J. Härri, F. Filali, and C. Bonnet, “Mobility Models for Vehicular
0.2 Ad Hoc Networks: A Survey and Taxonomy,” research rep. RR-
0 06-168, Institut Eurecom, Mar. 2007.
0 1 2 3 4 5 6 7 8 9 10 [13] D. Jiang, V. Taliwal, A. Meier, W. Holfelder, and R. Herrtwich,
“Design of 5.9 GHz DSRC-based vehicular safety
Message size 250 bytes
Vehicle Numbers communication,” IEEE Wireless Communications, vol. 13, no. 5,
Message size 500 bytes pp. 36–43, Oct. 2006.
Message size 1000 bytes
Figure 11. Average End-to-End delay between the ambulance and other
vehicles with different message size
V. CONCLUSION
In this paper we studied the full details of the WAVE
architecture and IEEE 802.11p standard for vehicular ad
hoc networks (VANET). We implemented the key
parameters of 802.11p in ns-2 network simulation using
realistic vehicular mobility model generated by
VanetMobisim traffic simulation. One scenario was
implemented in the simulation. We analysed three
important metrics in order to evaluate the performance of
IEEE 802.11p standards. 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.
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