50120130404054

International Journal of Computer Engineering and Technology (IJCET), ISSN 0976-
6367(Print), ISSN 0976 – 6375(Online) Volume 4, Issue 4, July-August (2013), © IAEME
547
AN EMPIRICAL STUDY TO COMPARE BETWEEN IEEE 802.11P AND
WAVE PROTOCOLS IN VANETS NETWORKS
Mostafa M. El-Said
College of Engineering and Computing, Grand Valley State University,
Allendale, Michigan, USA
ABSTRACT
Vehicular ad hoc networks (VANETs) are a class of ad hoc networks that are designed to
improve travelers’ safety, entertain travelers, and reduce fuel consumption and pollution. One of the
main challenges facing the VANETs deployment is network scalability, both in sparse and dense
network environments. Network scalability is defined as the network’s ability to handle the
admission and the hands-off of mobile VANET nodes without suffering a noticeable loss in
performance.
This work studied the contributing factors to the VANET network scalability problem and
proposes a solution based on the use of the IEEE802.11P and the IEEEE 802.11P with multi-
channels support standard. In this work, safety data is assumed to be available and hosted in a secure
back-end server. Promising results were obtained using NCTUns simulation engine that show that
VANETs networks’ performance running under IEEE802.11P with multi-channel support
outperform its correspondence running under IEEE802.11P only.
Keywords: IEEE802.11P, WAVE, VANETs Simulation.
1. INTRODUCTION
VANETs networks are an effort to make the Intelligent Transportation System (ITS) reality
by allowing the exchange of road traffic information or information of vehicles’ best interest such as
the nearest gas station or parking garage. In consequence, drivers can react promptly to road critical
situations events (such as the car in front of you suddenly broke down) by choosing an alternative
route as quickly as possible or proceed to the nearest gas station or parking garage [1, 2, 3 and 4].
In VANETs, vehicles are the only mobile nodes in the network system. Each vehicle has an on board
unit (OBU), that is cable of exchanging traffic alert messages including road conditions and other
vehicles’ position, speed, ..etc. Mobile nodes transmit data using two VANETs architectures: (i)
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Volume 4, Issue 4, July-August (2013), pp. 547-555
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Inter-Vehicle Communications (IVC) and (ii) Roadside-to-Vehicle Communication (RVC). In IVC
architecture, vehicles are equipped with one or more wireless adapter (multi-adapters node). They
communicate directly with others that are within communication range. In RVC architecture, fixed
units are known as Roadside Assistance Units (RSU), which collects the road conditions traffic and
disseminates it to VANETs nodes that are within its communication range. RSU may receive this
information from the wired network via a central traffic server. The traffic server aggregates traffic
information from a traffic cloud and ensure its correctness and data authenticity [5, 6, 7, 8 and 12].
There are two categories of MAC protocols that support data transmission in VANETs environment:
(i) The first protocol is defined by the IEEE 802.11P and uses acontention-based (Carrier Sense
Multiplex Access with Collision Avoidance (CSMA/CA) protocol with full implementation
of node joining process including node probing, association and authentication.
(ii) The second protocol is a family of protocols defined by the IEEE 802.11P and the IEEE
1609. The 802.11P protocol uses the Wireless Access in Vehicular Environments (WAVE)
with multi-channels extension supported by the IEEE 1609.4 protocol at the upper layers.
The system diagram of WAVE communications is shown in Figure 1. The WAVE enabled
OBU and the RSU units implement a full stack of the WAVE modules.
IEEE 1609.1
WAVE Resource Manager Application Layer
IEEE 1609.3
Networking
Services
IEEE 1609.2
Security
Services
Transport, Network and
Logical Link Layers
IEEE 1609.4
Multi-Channel Operations (MAC-
Extension)
Medium Access
Layer
IEEE 802.11P
WAVE MAC
IEEE 802.11P
WAVE PHY Physical Layer
Figure 1 WAVE system protocol stack. Figure is based in [10], [11]
In 1999, the Federal Communication Commission (FCC) allocated a 75 MHz of Dedicated
Short Range Communication (DSRC) frequency band in the 5.850-5.925GHz for ITS WAVE based
system utilization. This frequency band is divided into seven channels with 10 MHZ each. The IEEE
1609 family standards define two types of communication channels in WAVE based systems to
support safety and non-safety applications. The first channel is called Control Channel (CCH) which
is used to transmit WAVE Short Messages (WSMs) and announce WAVE services. The second
channel is known as Service Channel (SCH), which is used to transmit application/service data. In
any WAVE based system, only one CCH and one or more SCH will be needed such as described in
figure 2. Using more than one SCH will depend on the application requirements and the available
bandwidth [12].

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Figure 2 Distribution of service and control channels in time and frequency
This research work focuses on the scalability of VANETs deployment, supported by WAVE
protocol, both in sparse and dense network environments. Research work presented in [5, 7, 12, 13
and 11] addresses many factors that affecting the network scalability such as:
1. Number of admitted nodes to the network per lane,
2. High mobility of network nodes causing frequent handoffs with large overhead due to
network association/re-association procedures, and
3. Number of broadcasting safety messages: timing and relevance of safety messages to the
receiving vehicle based on its location and driving direction are vital factors in improving
the network scalability and reducing unnecessary broadcast traffic.
However, comparing the performance of VANETs deployment based onIEEE802.11P and
the IEEEE 802.11P coupled with multi-channels support is notcovered in the literature. Therefore,
the objectives of this research work are to:
1. Understand and apply simulation techniques to IEEE802.11P based VANETs networks,
2. Investigate why the existing MAC of 802.11P is not suitable for modern VANET
deployment,
3. Investigate the suitability of using IEEE802.11p coupled with multi-channel extension
(WAVE standard) as an alternative for the current VANET’s MAC layer and how this
choice may affect the network scalability characteristic.
The remainder of the paper is organized as follows. Section 2 introduces the simulation
environment and parameters. Section 3 describes and summarizes the conducted experiments and
simulation results. Section 4 concludes the paper and outlines future work.
Frequency
(GHZ)
5.925 SCH SCH
5.915 SCH SCH
5.905 SCH SCH
5.885 CCH CCH CCH CCH
5.875 SCH SCH
5.865 SCH SCH
5.855 SCH SCH
CCH
Interval
SCH
Interval
CCH
Interval
SCH
Interval
Time
Frame Interval Frame Interval

550
2. SIMULATION EXPERIMENTS
2.1.Simulation Engine Tool
In this study, the NCTUns (National Chiao Tung University Network Simulator) is used.
NCTUNs provides a coupled network and traffic simulator. By using a coupled model of simulation,
any changes in the traffic status is communicated to the network simulation and an immediate
feedback is sent back to alert vehicles on congested roads and possible lane changes. The NCTUns
simulation uses a novel kernel reentering methodology for carrying on the simulation task and it is
built on top of the Linux TCP/IP protocol stack for packet passes [14, 15].
Figure 3 shows the architecture of the NCTUNs simulation platform. The NCTUNs
architecture consists of four major components: GUI, SE, Car Agent(s), and Signal Agent(s). These
components play a major role in conducting the simulation task such as described below.
Component #1: GUI (Graphic User Interface)
The GUI provides users with the ability to construct different road network structures such as
road segments intersection, traffic signal and number of lanes per road segment. Once the
road network is ready, user can deploy the desired communication network technology and
topology. At this point the GUI will automatically generate all configuration files for the
other components. The GUI allows users to play back an animated session of packet
transmission and vehicles movement, which helps in troubleshooting and ensure correctness
of network protocol implementation.
Component #2: SE (Simulation Engine)
The SE is the coordinator among car and signal agents. SE is responsible for communicating
requests/responses messages among these agents as well as simulating transport-layer and
network-layer protocols.
Component #3: Car Agent
A car agent runs on each vehicle and composed of four sub-components:
i. agent logic: controls driver behaviors based on the road conditions
ii. road map database: supplies the shape/location of the road network
iii. socket interfaces: provides an interface layer between TCP/UDP layer and the layers
below to exchange application messages and road network information
iv. car/signal information APIs: these APIs are used to allow the agent logic access to the
car/road/signal information.
Component #4: Signal Agent (SA)
The signal agent runs on each crossroad intersection. SA controls the changing of the signal
state of the four traffic lights located at the crossroad intersection.

551
Figure 3 The NCTUNs integrated platform architecture. Figure based in [14]
NCTUns supports various ITS VANET standards such as IEEE 802.11 (a), (b) and (p).
Moreover, NCTUns supports different realistic road network constructions such as highways, city
streets and importing real road maps to study vehicles behavior in specific area. More information
about NCTUns simulator can be found in [1, 2, and 14].
Accurate simulation results depend on using realistic vehicular environment including
vehicles mobility patterns (highways as opposed to city streets), vehicles speed, and immediate
response to changes in road conditions [1, 2 and 14]. For this simulation study, roads network are
constructed using GVSU main campus roads structure such as shown in fig 4.
Figure 4 Simulation Environment
Road Map DB
Agent
Logic
Socket
Interface
Car/SignalInf
o APIs
TCP
Car Info DB Signal Info DB
Car
Agent
GUI
Protocol
Stacks
TCP/
UDP
SignalInfo
APIs
Agent
Logic
Signal
Agent
TCPTCP
TCP/
UDP
TCP
SE
Signal AgentCar Agent

552
2.2.Simulation Experiments Setup Parameters
Simulation experiments are carried out with different number of vehicles nodes (experiment-
1: 10 vehicle nodes, experiment-2: 20 vehicle nodes and experiment-3: 30 vehicle nodes). Vehicles
nodes are randomly distributed in the road network structure. Fixed and mobile VANETs nodes are
exchanging bacon signals that carry safety messages. The experiments are performed using the
vehicular 802.11P MAC and 802.11P MAC with multi-channel extension support. Simulation
parameters are collected to measure network throughput and determine how effective is each MAC
type and its impact on the network scalability design characteristic [4 and 5]. In each simulation
scenario, the experiments are conducted for 400 seconds in a 20 main road segments. Vehicles
agents will use the Intelligent Driver Model (IDM), namely, Car Following Mobility model that
controls the vehicles’ speed and direction. Also, IDM accounts for the presence of nearby vehicles
when adjusting their moving speed to avoid collision with the front car. Vehicles are moving
through the road structure with maximum speed of 25 m/s.
3. SIMULATION EXPERIMENTS RESULTS
3.1. Simulation Experiments Results (1)- Vehicular MAC 802.11P
Figure 5 shows the network throughput under various network loads for 802.11P MAC. The
network throughput is significantly affected by admitting new nodes into the network. Throughput
has dropped from 6.0Mbps to close to 1.0 Mbps in the three scenarios. This drop in throughput is
resulted from the MAC requirement of the 802.11P of having vehicles nodes send out probe requests
and an association request. Now, the vehicle node associates with the network and starts to receive
the safety alert messages. It is worth mentioning here that the time axis shows the performance
metrics up to 100 seconds. The reason for this is I found no change in the network performance
metrics values after 100 seconds.
(a)10 Vehicle nodes in the field with 1-BS(b) (b)20 Vehicle nodes in the field with 2-BS
(c) 30 Vehicle nodes in the field with 3-BS
Figure 5 Network throughput with various vehicle nodes in the field (802.11P)

553
3.2.Simulation Experiment Results (2)- Vehicular MAC 802.11P with multi-channel
extension support (WAVE Standard)
In this section, the VANET network is running 802.11P coupled with multi-channel
extension support. Therefore, all OBUs and RSUs are using the same channel. Figure 6 shows the
network throughput under various network loads. In comparison with the experimentation results (1),
the network throughput is significantly improved tremendously. It appears that the WAVE standard
does not use consume network resources by allowing vehicle nodes to join the VANET network and
then receive safety messages. In another way, there is no probe request/response or association
request/response. This process saves the network bandwidth and utilizes it efficiently in transmitting
safety messages.
(a) 10 Vehicle nodes in the field with 1-RSU (b) 20 Vehicle nodes in the field with 2-RSUs
(c) 30 Vehicle nodes in the field with 3-RSUs
Figure 6 Network throughput with various vehicle nodes in the field (802.11P with multi-channels
extension)
4. CONCLUSIONS
The presented work contributed to the following areas, (i) learning about different simulation
techniques especially the new methodology of Kernel re-entering technique and how to apply it to
VANETs networks and (ii) build realistic simulation scenarios and observe the VANETs network
performance under various load conditions and different MAC technologies such as 802.11P and
802.11P with multi-channel support. Therefore, the use of 802.11P coupled with the multi-channel
support would support the network scalability design criterion.
In the future, further consideration to message authentication technique will be given to
protect against broadcasting fake or false safety messages in VANET networks.

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5. REFERENCES
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2008.

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AUTHOR DETAIL
Mostafa El-Said has received the M.S. and Ph.D. in Computer Science and
Engineering from University of Louisville in 2000 and 2003 respectively.
Dr. El-Said’s research interests include designing Smart Autonomic VoIP
and VANET Systems. He is a member of the IEEE, and has served as a
Vice-Chair of the IEEE Computer Society Technical Committee on
Simulation (TCSIM) since 2005.Also, he is currently a member of the
international programme committee and a reviewer for IEEE
SmartGridComm, IEEE CCNC, SIMUTools, CGAMES and IJIGS. Dr. El-
Said joined the faculty in The Pennsylvania State University, Information Sciences and Technology
(IST) School in 2003. Since 2004, he has been with the Grand Valley State University (GVSU),
where he is currently an Associate Professor in the School of Computing and Information Systems
and Chair of the Information System Program. He is the founder and the director of the Wireless
Systems Lab and the director of the Data Communication Center in GVSU.

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