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Vehicular ad-Hoc networks (VANETs)—An overview and challenges


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Vehicular ad-hoc networks (VANETs) technology has emerged as an important research area over the last few years. Being ad-hoc in nature, VANET is a type of networks that is created from the concept of establishing a network of cars for a specific need or situation. VANETs have now been established as reliable networks that vehicles use for communication purpose on highways or urban environments. Along with the benefits, there arise a large number of challenges in VANET such as provisioning of QoS, high connectivity and bandwidth and security to vehicle and individual privacy. This article presents state-of-the-art of VANET and discusses the related issues. Network architecture, signal modeling and propagation mechanism, mobility modeling, routing protocols and network security are discussed in detail. Main findings of this paper are that an efficient and robust VANET is one which satisfies all design parameters such as QoS, minimum latency, low BER and high PDR. Some key research areas and challenges in VANET are presented at the end of the paper.
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Journal of Wireless Networking and Communications 2013, 3(3): 29-38
DOI: 10.5923/j.jwnc.20130303.02
Vehicular Ad-Hoc Networks (VANETs) - An Overview
and Challenges
Sabih ur Re hman*, M. Arif Khan, Tanveer A. Zia, Li h o ng Zhe ng
School of Comp uting and Mathematics, Charles Sturt University, Australia
Abs t ra c t Vehicular ad-hoc networks (VANETs) technology has emerged as an important research area over the last few
years. Being ad-hoc in nature, VANET is a type of networks that is created from the concept of establishing a network of cars
for a specific need or situation. VA NETs have now been established as reliable networ ks that vehicles use for communication
purpose on highways or urban environments. Along with the benefits, there arise a large number of challenges in VANET
such as provisioning of QoS, high connectivity and bandwidth and security to vehicle and individual privacy. This article
presents s tate-of-the-art of VANET and discusses the related issues. Network architecture, signal modeling and propagation
mechanism, mobility modeling, routing protocols and network security are dis cussed in detail. Main findings of this p aper are
that an ecient and robust VANET is one which satisfies all design parameters such as QoS, minimu m latency, low BER and
high PDR. Some key research areas and challenges in VANET are presented at the end of the paper.
Ke y wo rds VA NET, Modeling, Mobility, Routing, Security
1. Introduction
Although Vehicular Ad-hoc Network (VANET) is not a
new topic, it continues to provide new research challenges
and problems. The ma in objective of VANET is to help a
group of vehicles to set up and maintain a communication
network a mong them without using any central base station
or any controller. One of the major applications of VANET
is in the critical medical emergency situations where there is
no infrastructure while it is critical to pass on the information
for saving human lives. However, along with these useful
applications of VANET, emerge new challenges and
problems. Lack of infrastructure in VANET puts additional
responsibilities on vehicles. Every vehicle becomes part of
the network and also manages and controls the
communication on this network along with its own
communication requirements.
Veh ic u la r ad -hoc networks are responsible for the
communication between moving vehicles in a certain
environment. A vehicle can communicate with another
vehicle directly which is called Vehicle to Vehicle (V2V)
communication, or a vehicle can communicate to an
infrastructure such as a Road Side Unit (RSU), known as
Ve hic le -to-Infrastructure (V2I). Figure 1 shows a typical
VANET scenario.
The main contributions of this paper are to present state
* Corresponding author:
sareh man @cs u. edu. au (Sabih ur Rehm an)
Published online at
Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved
of the - art in VANET technology. A detailed study of
network architecture with dierent topologies and network
modeling is presented in this paper. A key design area in
VA N ET i n order to properly form a communication network
is routing the packets in effect ive manner. The paper
discusses dierent routing algorithms for VANET and
pres e n ts limitations of those algorithms. Security issues in
VA NET environment are also addressed in the paper so that
trustworthy network architecture can be modelled. The paper
also discusses some of the key research areas and challenges
in th is fie ld .
1.1 . Background Research
A very important design aspect of VANET is to develop
an ecient, reliab le and secure routing protocol. Va st
research has been conducted in thisarea[1],[2],[3],[4],[5],
[6],[7],[8],[9],[10],[1 1],[ 12],[13],[ 1 4], [15],[16]. The main
objective of any routing protocol is to find an optimal way of
communication between nodes ( veh icle s ). One popular
VA NET routing protocol is Ad-hoc On Demand Vector
Routing (AODV) p resented in[17, 18] which uses a
demand-driven route estab lis hment procedure. A limitation
of this approach is that it creates flooding type of situation
within the entire network. Many researchers have presented
the remedies for flooding in AODV[19, 20]. Another routing
approach is presented in Dynamic Source Routing[21] which
is also classified as reactive in nature. Routes are stored in
cache and it is expected that source will have co mplete
knowledge of hop-by-hop route to the destination. In[22],
authors have presented another routing approach using bor-
der node concept. This protocol was based on stop and carry
30 Sabih ur Rehman et al. : Vehicu lar Ad -Hoc Networks (VANETs) - An Overview and Challen ges
There are many important applications of VANET in
todays world. These applications range from critical
medical services to comfort and leisure activities. A VANET
must be able to full all require ment of ever changing user
needs and should also comply with the standard and
architectures of the available technology.
Some of the key applications[9] of VANET can be sum-
marised as follows:
Fi gu re 1. C re at ing an Ad-ho c Net work usin g Veh i cles (VANETs)
Road Tra
c Safety -Work on reducing the number o f
fatalities/injuries on the roads by alerting the driver about
dangers in advance.
c Engineering or E
ciency - Increase overall
performance of the transport systems by reducing travelling
time and congestion.
Comfort and Quality of Road Travel- Provide comfort
applications for travellers like ‘advanced traveller
informat ion systems’, ‘electronic pay me nt s y s t ems ,
‘variable mess age signs’ and ‘electronic toll collection’ etc.
Some of the key characteristics of a VANET model are as
follows :
Dyn amic Topology: VANET environment has a
constantly changing topology due to high mobility of the
vehicles. The connection between two vehicles travelling
with average suburban speed limits in opposite directions
lasts for a very short time. This connection time goes much
lesser as the speed of the vehicles increases in a
freeway/highway environment.
Frequent Disconnections: The link connection between
the vehicles in VANET has frequent disconnections because
of the high movement of the nodes and frequent change in
the environmen t .
Mobility Modeling: In order to implement VANET
efficiently and realistically, an accurate mobility model is
required for this highly dynamic environment of VANET.
Predictable Mobility Patterns: In VANET environment
most of the vehicles move on pre-defined roads and
highways. This allows the use of predictable mob il ity
patterns in network design.
Use of Other Technology: Most of the vehicles in VANET
these days are capable of integrating their own system with
other available technologies such as Global Positioning
Sys t em (GP S).
No Power Constraint: As compared to other Mobile
Ad-hoc Network (MANET) devices, the nodes in VANETs
have the privilege of having longer battery life. This can be
utilis ed fo r e cient processing of comp le x a nd
computational hungry routing/security mechanisms in the
Stringent Delay Constraints: VAN ETs are responsible for
the delivery of critical medical emergency messages. These
messages must be delivered on time in order to save human
lives .
The rest of the paper is organized as follows. Section 2
presents the architecture and network modeling of ad-hoc
ne tworks. Dierent routing paradig ms and algorith ms along
with their pros and cons are discussed in Section 3. Security
aspects of VANET are discussed in Section 4. Section 5
highlights the key research areas and the challenges in the
field. Section 6 concludes the paper.
2. Architecture and Network Modeling
In princ ipal, there is no fixed architecture or topology that
a VA NET must follow. However, a general VANET consists
of moving vehicles communicating with each other as well
as with some nearby RSU. A VANET is dierent than a
MANET in the sense that vehicles do not move randomly as
nodes do in MANETs, rather moving vehicles follow some
fixed paths such as urban roads and highways. While it is
easy to consider VANETs as a part of MANETs, it is a lso
important to think of VA NETs as an individual research field,
especially when it comes to designing of network
architecture. In VANET architecture, an on board unit (OBU)
in a vehicle consists of wireless transmitter and receiver.
Fi gu re 2. N et work Arch itecture in VANET
In a broad sens e, we can loosely define three possible
communication scenarios for vehicles. One possibility is that
all vehic les communicate with each other through some RSU.
This architecture may resemble wireless local area networks
(WLAN). Second possibility is where vehicles directly
communicate with each other and there is no need of any
RSU. This can be classied as Ad-hoc architecture. In third
possibility, some of the vehicles can communicate with each
other directly while others may need some RSU to
communicate. Th is can be referred as hybrid scenario[23].
Figure 2 shows these three possibilities.
Understanding of network architecture is important in
order to realise the full potential of vehicular communication.
Most of the researchers[24, 25 ] hav e based their studies by
dividing VANET s cenarios in three categories namely Urban,
Journal of Wireless Networking and Communications 2013, 3(3): 29-38 31
Rural and Freeway/Highway.
One of the reasons to investigate in such a manner is to
make sure that it will eventually cover the need of
inter-networking for entire vehicular environment. Each
environment has its own specific challenges to overcome.
For example, in a sparse network like highways, the low den-
sity of vehicles remains the prime issue. Even in some urban
environments, low penetration ratio and low trac at night
times can cause long network delays.
One of the most important attributes of mobile ad-hoc
wireless network is the mobility associated with the nodes.
The highly mobile nature of vehicles makes it very
complicated to model the communication scenario. Mobility
model for a VA NET environment has to look deeper into key
characteristics of vehicular mobility like acceleration,
deceleration, changing lanes and human driving patterns. For
this purpose, an ample amount of research[26, 27, 28 ] h a s
been made to include mobility in the design of VANET. In
VA NET paradigm, the mobility model must include the
behaviour of moving vehicles individually and in a group for
an erro r free e cient packet transmission.
Generally, a mobility model can be classied at micro and
macro levels depending on the nature of details required in
modeling. The consideration for roads, buildings and streets
are classified as macroscopic whereas the behaviour of
vehicles is treated as mic roscopic level[9]. In general, the
mobility models in VANET can be categorised in three
categories such as: a) Stochastic or Random Modeling, b)
Trac or Flow based Modeling, and c) Trace based Mod-
elin g [28]. Th is ranges from the fluid flow theory to stochastic
theory which includes random walks and the aggregated
behaviour of the vehicles. On the other hand, the mobility
modeling can also be based on the degrees of randomness in
the model one wish to include. Many researchers used
deterministic approach, hybrid approach or total random
approach to model the dynamic nature of vehicles in a
VA NET. Mobility modeling impacts on the performance
an a lys is of the networks such as on end-to- end delay,
capacity, security, routing, and scalability of the networks
few to name[2 9].
A more concrete network modeling for ad-hoc networks
can be done using appropriate mathematical and statistical
tools[30]. In one of the approaches, a wireless ad-hoc
network can be modelled as a random graph with vertices of
the graph representing nodes and edges in the graph may
represent commun ication links between the nodes[31]. A
graph model of mutli-hop wireless network can be
represented as G = (V, L) where V is the vertex set and L is
the edge set of the graph. Such a graph can be constructed
using Random Geo metric Graph (RGG), where vertices are
independent and identically distributed in a specic area
satisfying the Poisson Distrib u t io n . Th is mod el is s imilar to
the connected graph of a Boolean Model (BM)[32]. A mo re
theoretical and analytical understanding of this topic has yet
to be done for ad-hoc wireless netwo rks .
One of the most challenging areas of research for VANET
is the actual transmission and reception of the signal. The
wireless channel through which the signal propagates is
highly dynamic in nature. It is full of different scatterers,
reflectors and absorbed by many objects during the
transmission. Therefore, it is of utmost importance to
properly model the signal which helps in correct recovery of
the transmitted signal. At the receiver side, generally signal
does not take single path to arrive. There are mult i-paths for
the signal to arrive at the receiver. One of the challenges is to
combine these different components of the received signal in
such a way that the correct data must be recovered.
Let us consider that is the complex Gaussian
received signal with zero mean and unit variance at one of
the nodes and is given by the following equation
= + , (1)
where × is the co mp lex channel gain matrix,
is the co mplex trans mitted signal and is
additive white Gaussian noise. In order to minimise the bit
error rate and provide the promised QoS, one has to reduce
the effect of wire less channel on the received signal. For this
purpose a number of wireless channel models such as Free
Space Model[59], Nakagami Model[58] and Log Normal
Shadowing Model have been considered. These models also
play an important role in creating the simu lation
environment for different VANET scenarios. For example,
NS-2 uses Nakagami model whereas OMNET++ by defau lt
uses Free Space Model. In any VANET environ ment,
calculating the transmission range and then finding the
probability of packet delivery ratio (PDR) is important.
Transmission range for a Free Space wireless channel model
can be calculated using Friis Transmission equation[60]
given as
= 2
(4 )2
, (2)
are receive and transmit powers
respectively, and are gains of transmit and receive
antennas respectively, λ is the wavelength and is t h e
distance between transmitting and receiving nodes.
Considering proper propagation scheme, wireless channel
model and combining schemes at the receiver imp roves the
QoS in VA NET.
3. Routing in VANET
One of the major challenges in the design of veh ic u lar
ad-hoc network is the development of a dynamic routing
protocol that can help disseminate the information from one
node (vehicle) to another. Routing in VA NET is dierent to
the traditional MANET routing because of highly dynamic
and ever changing topologies in the former. Few protocols
that were earlier designed for MANET environment have
been tested on VANET. The challenge however remains as
how to reduce delay associated with passing the information
from one node to another. Overcoming these hurdles in
MANET protocols, can help implement real time appli-
cations for VANET environment. Other implications such as
reducing control overheads also need to be looked into
32 Sabih ur Rehman et al. : Vehicu lar Ad -Hoc Networks (VANETs) - An Overview and Challen ges
carefully. Keeping an eye on the dynamic characteristics of
VA NET (as highlighted previously), the routing protocol
should be able to withstand the unpredicted and dynamic
nature of vehicular network topology. Perhaps the most
dicult task in VA NET routing is finding and maintaining
the optimal paths of communication in desired environments
Most of the routing protocols in VA NET are closely
lin ked wit h the topology being used in the network
architecture and the performance deviates whenever there is
a change in network topology.
As highlighted in Figure 3, routing in VANET can be
classified into five major categories namely as:
Ad-hoc or Topology Driven Protocols
Location Based Routing Protocols
Cluster Based Protocols
Broadcast Protocols
Geocast Protocols
3.1 . Ad-hoc or Topol ogy Dr i ve n Routi ng
In general, VA NETs are inf rastructure -less networks a n d
many routing protocols devised for prior ad-hoc network
such as MANET based on dierent network topologies may
be applied to VA NETs with certain modifications. Topology
driven protocols are sub-classified into three categories such
as proactive, reactive and hybrid. A number of such
protocols were designed to cater the needs of VANET
environmen t [17],[2 1] ,[22], [33],[34]. In a proactive protocol,
nodes continuously update their routing table with
information regarding ne w routes within the network. This
informat ion is passed around to all nodes by sending periodic
HELLO pac kets. This approach, however, creates su bs tantial
control overheads. This restricts the use of limited wireless
resource such as available bandwidth.
On the other hand, in reactive approaches, for example
AODV[17], DS R[21] , BRP [22] nodes will only send the
control data when there is a need. This reduces overheads
associated with establishing the link, and helps distribute the
actual information faster. This approach however still puts
undue resource overheads like maintenance of used/un us ed
routes. These unused paths are created and broken, due to
s t ringent network topology of VA NET. Overheads created in
reactive protocols are associated with discovering the path to
send the information. The path finding process is initiated by
sending certain type of message called Route Request
Message (RREQ).
In Figure 4, node (S) wants to send information to node
(D). This process will be initiated first by discovering of
route to the destination. When node S needs to find a route to
node D, it broadcas ts an RREQ mess age to all its neighbours.
When intermediate nodes, say node 1 receive a RREQ
message, they compare the desired destination with their
own identifiers. If there is a match, it means that the request
is destined for node 1, otherwise, node 1 will rebroadcast the
RREQ to its neighbours and so do all the other nodes. This
approach can create a flooding in the network. Once the
request reaches the destination (node D in this case), Route
Reply Mess age (RREP) is initiated back to the source using
Backward learning method.
Besides studying basic reactive and proactive type of
protocols, researchers have found tremendous liking to
discover hybrid protocols as well. An examp le of such a
protocol is discussed in detail in[33]. In this approach, the
authors have focused more on the design architecture of
whole network rather than the performance analysis.
Fi gu re 3. Ro utin g Types in VANET
Journal of Wireless Networking and Communications 2013, 3(3): 29-38 33
Fi gu re 4. Traditional Rout ing -Route Discovery using Flooding
One protocol that has shown robust behaviour against the
topology change is Temporally Ordered Routing Algorithm
(TORA)[35]. It sends localised routing messages to a small
set of node in the vicinity of the change. In TORA there is a
potential for oscillation to occur, especially when various
sets of nodes are trying to be a part of one space set.
3.2 . Loc atio n B ased R outing
Another category of protocols that have shown interest
among the researchers are Location or Position Based
Routing protocols. In this scheme of protocols information
regarding geographic location of vehicles is obtained from
dierent sources like maps, Global Positioning System
(GPRS) or even traces of trac models to help disseminate
the information. Quite a few researches like[36] and[37]
have presented a thorough comparison of well known
topology based protocols like AODV and DSR in con-
junction with Position Based algorithm and the results have
shown better and improved performance as compared to
using plain topological approach.
Unlike topology based protocols, position based protocols
do not need any route maintenance and the route can get
established when there is a need for it. This reduces undue
constraint on the bandwidth that is already inadequate in
VA NET environment. Greedy Perimeter Stateless Routing
(GPSR)[38] is one of the examples of a location based
protocols where search for nearest neighbour is performed.
Each node is aware with its position as well as the position of
its clos est neighbours. Having the main node this specific
information makes GPSR highly suitable for dynamic
topological networks. In scenario where no nearest neigh-
bour exists, GPSR utilises perimeter mode with face routing
to maximise the search for destination. A performance
comparison of GPSR and DSR in a highway environment
has been presented in[37]. It has been shown that an
improvement in route delay is achieved while using GPSR.
In applications where delay and Packet Delivery Ratio
(PDR) have stringent requirements mostly in urban
environment, GPSR in its original form cannot be used. To
cater this problem,[39] presented a modified version of
GPSR called Advanced Greedy Forwarding (GPSR-AGF).
In this version, information about speed and direction of the
destination node are included within the HELLO packets.
This showed an improvemen t in re lation to the above
mentioned performance metrics. To overcome the
deficiencies of GPSR, another approach was presented by
the introduction of Geographic Source Routing (GSR)[40].
In GSR, road layouts are used to discover the destination
route. It mostly relies on availability of road maps which are
used in conjunction with the shortest path nding algorit h ms .
Another important location based routing approach was
presented in[12],[13] namely Location Assisted Routing
( LA R). LA R is cla s sified as a reactive protocol which us es
location information of nodes to decrease the routing
overheads that were underlined by other reactive protocols
such as AODV and DSR. LAR mainly employs two methods
to determine the next hop, one based on window size and
other with distance variation.
In[13], authors have presented a study of LAR scheme for
VA NET in Highway scenario using the performance metrics
s u ch as Packet Delivery Ratio (PDR), System Throughput,
Average Delay and Routing Overheads. It is shown that the
PD R in creases for moderate number of nodes but decreas es
at a higher network density. The reason being that at higher
network density, the connectivity between nodes is high
resulting in less loss of packets. The system throughput of
LA R increases from low to moderate network density but it
decreases when the number of nodes is higher than 50 in the
network. The reason for decrease in system throughput could
be the high in te rfe rence among the transmitted signals .
Routing overheads and average delay decrease with the large
number of nodes because of many routing paths and larger
number of hops.
A dierent methodology not relying on external resources
like maps or infrastructure is presented in Greedy Perimeter
Coordinator Routing (GPCR)[41]. GPCR is based on the u-
derstanding that street paths in urban environment create a
planner graph. Packets are always forwarded to a node
(coordinator) that is on the junction edge. The routing deci-
sions are only made by the coordinator. In another routing
scheme where routing decisions are made based on the
connected paths between source and destination pair is
Connectivity Aware Routing (CAR)[42]. Anchor-Based and
Trac Aware Routing (A-STA R) [36] is another position
based protocol used for urban environments. It exploits the
usage information for a particular route, to determine the
anchor path (number of junctions) to establish maximu m
connectivity. This usage can be determined us in g s t atist ic a l
data gathered for particular surroundings. If packet
(information) is needed to be sent to any node in between an-
chors, the usual greedy approach is used. Studies have shown
a much improved performance by using A-STA R as
compared to GSR and GPSR[43].
3.3 . Clus ter Base d Routing
In order to reduce the network trac and routing
34 Sabih ur Rehman et al. : Vehicu lar Ad -Hoc Networks (VANETs) - An Overview and Challen ges
overheads in VANET, a routing paradigm namely Cluster
Based Routing (CBR) is introduced in[44] ,[4 5], [46],[47].
The main idea behind CBR is to create a network
architecture based on s mall groups of vehicles called as
clusters. In a cluster, one of the vehicles plays the role of a
cluster-head as shown in Figure 5. The size of the cluster
depends on the design of the routing a lgorith m wh ich may be
based on the number of vehicles in a cluster or the
geographical position of the veh icles .
Fi gu re 5. Cl ust er Based Routin g
The concept of CBR is not new to ad-hoc networks. There
are studies in literature to test the performance of CBR in
MANETs where network conditions are rigid[44]. Most of
these routing protocols are based on first establishing a
mechanis m or protocol to create the cluster range, and then
looking into searching the optima l routes for communication.
Due to scalability issue, the cluster formation techniques in
MANET can’t be directly applied to VANET.
In LO RA -C BF [45], authors have presented a reactive
geographic routing based algorithm for V2V communication
by introducing one cluster head, zero or mo re me mb e r s o f
the cluster and one or more gateway to communicate with
other cluster-heads. The architecture of the LORA-CBF
helps to minimize the unnecssary overheads of
retransmissions. Firstly, as in reactive approach, routes in
LO RA -CBF are updated only when there is a need for it to be
updated. Secondly, it uses a concept of having vehicular
gateways to pass control information and hence reducing the
control trac overheads. Cluster-head is responsible for its
cluster and sends periodic beaconing messages to update its
parameters. Only gateways and cluster-heads are allowed to
retransmit the route discovery packets, Location REQuest
(LREQ) packets where LREQ are packets same like RREQ
packets in topology driven protocols such as AODV and are
transmitted to gather location information of other clusters.
LO RA -CBF can be suitable for highly mobile environment
li ke VA N ET b ecause it updates the location information of
clu s ters rather than the individual vehicles. Simulation
results have shown better performance by LORA-CBF as
compared to other reactive routing protocols like AODV and
DSR[45] .
In[4 6] , a u thors have presented another approach in
designing of a cluster based routing protocol where they
divided the included geographic area into grids. Depending
on number of vehicles in the grid area, the vehicles are
selected as leader of the group. When the source vehicle
wants to send information to destination, it doesn’t need to
discover the whole route, it just forwards the data to optimal
neighbour cluster-head. The data will then be disseminated
to the destination (in the cluster) by the cluster head. This
minimises the overheads associated with the data dissem-
ination and saves the memory space needed to store routing
In[47] authors have presented another cluster based
routing scheme with the main objective of achieving better
results for network topology stability as well as decreasing
the dynamic natu re of VAN ET. The routing algorithm
co ns id ers the speed dierences among the vehicles in
addition to the geographical location and destination of the
vehicles. The performance of proposed threshold based
algorithm is compared with other position based and weight
based algorithm in terms of the change of average number of
clusters. It is shown that the average cluster change per
vehicle with the proposed algorith m is much smaller
compared to other routing protocols. This concludes the less
dynamic nature of the algorithm.
3.4 . Broa dc as t Routi ng
Broadcast Routing was one of the traditional routing
techniques used in VANET. Primarily broadcast approach is
used when the message is needed to be sent to the vehicle
that is outside the range. Packets are transmitted using
flooding techniques. This ensures delivery of information,
but uses extensive resources of bandwidth. As briefed
previously, this sort of technique is utilised in many well
established routing protocols, especially in the stage of
discovering of route to the destination. BROADCOMM[48]
and the Nth-Powered P-persistent Broadcast protocol (NPPB)
[49] are such well known protocols designed using the
broadcasting concept.
In BROADCOMM, a hierarchical structure of highway is
simulated and the whole region is divided into virtual cells.
Ce ll me mb e rs es tab lish a hierarchy of Cell Reflector ( CR),
which acts like a base station to gather mess ages for
particular call as well as from neighbouring cells. CR helps
in making judgements in relation to forwarding the messages
to individual vehicles. This protocol has shown an imp roved
performance in message broadcasting, delay and routing
overheads when compared with other broadcasting protocols.
In N PP B[4 9] a probabilistic broadcasting approach is
designed to mitigate broadcasting storms in dense VANET
in order to transmit emergency messages eectively. The
authors studied a weighted p-persistent routing scheme
which shows better accessibility of the farthest node. The
performance of this protocol depends on a reasonable choice
of the number of nodes in the environment.
3.5 . Geoc as t Routing
Geocast routing is the classification of routing that deals
with d issemination of information in specific area of
relevance. Since the early induction of VANET, quite a few
approaches of Geocast routing werepresented[10],[11 ],
Journal of Wireless Networking and Communications 2013, 3(3): 29-38 35
[12] ,[13],[14],[15], [16]. Many VANET applications require
position dependent multi cas ting e.g . d iss emin at inghazar
dous trac information to vehicles approaching in the same
direction. The key idea behind the Geocast routing is to
narrow down the search for next hop to a specific Zone Of
Relevance (ZOR). Imagine the possibility of having a
mechanism in which if a car gets involved in an accident, it
will automatically report the accident to the approaching
vehicles within that zone.
In[10], authors have presented a Geocast routing protocol
by submitting design architecture of RObust VEhicular
Routing (ROVER). In ROVER, only control packets are
flooded in the network and the data is disseminated using
unicast approach that in turn increases the eciency and
reliability of the routing scheme. In ROVER, a ZOR is
created as a rectangular window at the back of the source
node. The dimensions of the window created are defined as
length (L) and width (W) respectively. The size of the
window is decided such that all of the lanes on the current
road are covered. The node (vehicle) will accept the mess age
if it rece iv es it wh ile it was in ZOR and re ject it if it is no t
within that zone. It was shown in[10] that ROVER presents
better results for low density environments.
In[14], authors have presented a geographic routing
scheme, GROOV, for both city and highway scenarios based
on the geographical routing strategy presented in[15].
GROOV is based on the idea of finding the most suitable
relay node rather than on the greedy selection criteria. Most
of the greedy selection schemes a re based on improving the
average end-to-end delay while compromising on PDR. It is
shown that GROOV achieves higher PDR co mpared to the
routing algorithm presented in[15] for city environ ment.
In order to localize the search space by using node
positions and map information, there are few techniques
which a re based on this idea. In[16], authors have presented a
context based routing protocol, VCARP, which uses vehicles
information such as destination, location and packet cache
state to make optimal routing decision. The packet
retransmissions are avoided by storing them temporarily in a
cache. Simu lations studies have shown that VCARP
achieves better PDR and reduces the routing overheads in
VANET scenarios. Another vehicle assisted routing protocol
for VANET is presented in[50] and is ca lled Vehicle Assisted
Data Delivery in Ve h icu lar Ad -hoc Network (VADD). In
this protocol authors adopted the concept of carry and
forward. Four dierent variants of VADD are presented and
their performance is compared with each other. It is shown
that the proposed VADD protocols have better performance
in terms of PDR, Average End to End delay and routing
overheads compared to other existing protocols. Among the
dierent variants of VADD, the H-VADD out performs the
other three.
4. Security in VANET
Security in VANET should be considered as important as
securing other networks in computing. Due to the highly
sensitive nature of information be ing broadcasted via
VA NET, all applications designed for vehicular network
need to be protected from malicious man ipulation. Imagine
the possibility of a critical message been manipulated and the
harm it will cause if not detected. In addition to that, comfort
and quality applications in VANET need to be protected to
prevent loss of revenue. Va rious consortiums like Network
on Wheels ( N OW ) [51] and Secure VehicularCommunicat
ions (SEVECOM) [52] are running with prime focus of
addressing security issues within the vehicular networks.
As per basic computer and network security definit ions
[53], attacks on a computer network can be classified in three
main groups of threats; threats associated with Authenticity,
Confidentiality and Availability of the resource. If one
applies this model of security on vehicula r network, the one
threat that really stands out is the Confidentiality of the
For example, an attacker who is busy in analysing which
certificates are attached to each message distributed in the
system, might also be able to track the exact location of the
vehicle (compromise of privacy). Currently a broadcast
authentication scheme is utilised in current standards of
security for VA NET such as IEEE 1609.2. This scheme is
based on the use of a public key signature. Broadcast
authentication enables the receivers to verify that received
informat ion was really s ent by the cla imed sender. In order to
protect the privacy of the node, few approaches have been
adopted[54] ,[55].
In[54], authors presented an approach of loading each
vehicle w ith mult iple ce rtified p ublic keys instead of only
using one default key. In another approach[55], authors have
presented a scheme of using pseudonym pools of identifie rs
in which vehicles are allowed to s witch between dierent
identities. One limitation of these approaches is that they put
undue processing constraints on the network that is already
being pushed to the limit due to the lack of bandwidth. In
order to understand how to develop a secure vehicular
network, one has to really consider the ‘Attacker Model’ and
the types of attacks which are encountered in VANET.
Usually attackers are led by their own motives like curios it y ,
malignity or just a competitive spirit. An attacker might have
access to inside knowledge and can be class ified as an inside
attacker which poses same level of threat as an outside
A better approach in VANET security could be to provide
an authentication mechanism to each node. In[56], authors
have presented such a security method which encourages the
nodes to provide a secure sender authentication. Due to the
large number of independent network members (vehic les)
and the existence of human factor, misbehaviour can take
place. So an authentication trust needs to be established.
In VANET security, the attack threats can be classified
into dierent categories. In[57], authors have described three
key types of attacks:
Bogus Information:- An inside attacker can make bogus
36 Sabih ur Rehman et al. : Vehicu lar Ad -Hoc Networks (VANETs) - An Overview and Challen ges
safety messages to be distributed in the entire network. This
can cause disastrous situations (a threat to Authenticity).
ID Disclosure:- Location information in relation to
vehicle’s exact position (privacy) needs to be protected (a
threat to Confide n t ia lit y ).
Denial of Service:- Attackers can potentially flood the
entire network so that no one will be able to use the applica-
tions/services. Such circums tances can create catastrophic
s it u atio ns if tr igg e re d in s tantaneously (a threat to
Availab ility ).
The two key challenges in re lation to providing a secure
communication in VA NET can be briefly classified as
establishing a robust s ys tem of sender authentication and
providing a mechanis m to keep the user location undisclosed.
Since vehicles are boosted with sucient processing power,
the computational resources needed for applying
cryptographic techniques in real-test bed should not be a
concern. On the other hand, if needed to be implemented in
virtual (simulated) environment, computational resources
required such as speed of processor and desired memory will
need to be looked into.
5. Ke y Research Areas and Challenges
Although there has been an ample amount of research in
VANET, still there are many areas which need to be looked
into. Due to the dierent nature of VANET form many other
wireless communication networks and hard design re-
quirements, there are many interesting research problems in
this field. The paper s ummarizes some of the key research
areas and challenges as under. However, it must be noted that
the research challenges in VANET are not limited to only
these areas.
(a) Quality of Service (QoS): Provision of certain quality
of service levels in VANET is an important task. A network
with min i mum delay for data delivery, less retransmissions,
and high connectivity time can provide certain QoS
guaranteed to the users. Promising this kind of QoS with
dierent user applications and dynamic network en-
vironment is an interesting and challenging task in VANET
(b) E
cient Routing Algorithms Design: In order to
timely and properly sending data packets from one node to
another node an ecient routing algorithm is required. In
VA N ET , e cient routing algorith m means a routing scheme
with min imu m delay, ma ximu m system capacity and less
computation al comp lexity. Design such an algorithm which
can be implemented in multiple topologies of the network
and satisfies all of the above mentioned properties is an
active area of research in VA NET.
(c) Scalability and Robustness: Designing a scalable and
robust network remains an open area of research in VANET
because of its challenging characteristics. Many design
approaches fall short when VANETs transform fro m spars e
to high dense mode, or from high mobility to slow trac
scenarios. A complete VANET framework that is scalable to
dierent network scales and robust to the topological
changes is required. This is an emerging area of research for
VA NET environment.
(d) Co-operative Communication: A key challenge in
VAN ET is es tab lishing the communication among dierent
nodes. Dierent concepts of co-operative communication
fro m wire less network theory may not be directly applied to
VA N ET . T h is c o -operative commun ication, such as up to
which extent nodes should e xchange information among
themselves, is one of the key research areas in the VANET
(e) Network Security: As the nodes in VANET
environment seek exchange of information among each other
all the time, making sure that certain c r itica l p riv acy
information rema in s wit h in the concerned node is an im-
portant design aspect. Designing a proper authentication
mechanism and a trust based security protocol is an
interesting and open research area in VANET.
6. Conclusions
This paper presented an overview and tutorial of various
issues in VANET. Various types of research challenges are
highlighted in context of vehicular communication. In
particular, this paper presented a review of VANET
architecture, transmission modelling, mathe matical aspects
of signal modelling, routing protocols and security. A
comparative analysis of dierent routing algorithms in the
field of VANET has been presented. It also highlighted the
main issues in routing algorithms. The performance metrics
for routing algorithms, discussed in this paper, were PDR
with respect to average velocity of vehicles, node density and
system throughput. The other parameters of interest
discussed widely in the paper were average end-to-end delay
and routing overheads. The paper concluded that some
algorithm perform we ll in urban environment while others
are suitable for highway environment. It was also concluded
that proper modeling techniques are necessary for designing
a seamless communication in VANET for a particular
environment. Finally, main research challenges and areas of
interest in vehicular commun ication were discussed.
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... It is difficult to determine appropriate criteria for cluster head election and cluster membership in a highly dynamic system like VANET, where automobiles are constantly joining and leaving the cluster. Vehicle clustering in VANET is accomplished using one of two methods: Road Side Units (RSUs) serve as static cluster heads in static clustering, which is based on V2I communication [6,7]. Cars are basically linked to RSUs in order to have real-time communication and Internet connectivity. ...
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Vehicle ad hoc networks, also known as VANETs, are characterized by their dynamic nature, exceptional mobility, and random network architecture. The functionality of the Transmission Head Arrangement on WSN can be hindered by a number of problems, some of which include frequent connection delinquencies, adaptabilities, various-bounce, data transfer, and data loss. In order to solve the issue, the authors of this work propose implementing a portability-aware region occupied routing in VANET. As the ideal approach for routing, a hybrid optimization strategy is implemented. The hybrid technique achieves optimal outcomes by employing both ant colony optimization (ACO) and artificial bee colony optimization (ABCO). When constructing the fitness function, connection stability and residual energy were both taken into account. Various indicators, including the delivery ratio, the amount of time, and the overhead expenditures, are used to evaluate the plan's effectiveness. Unlike the performance of other algorithms, the efficacy of the proposed technique is superior.
... Effective survivability algorithms like one mentioned in Hasita Kaja et al., (2021) are required to ensure reliability of the network while mitigating risks associated with security and privacy [3]. Vehicular Ad-hoc Networks (VANETs) refer to a type of wireless communication network that enables vehicles to communicate with each other and with the surrounding infrastructure [4], [5]. VANETs are specifically designed for vehicular environments, where vehicles act as mobile nodes in the network, forming temporary connections to exchange information in a decentralized manner. ...
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Vehicular Ad-hoc Networks (VANETs) play a crucial role in enabling efficient and safe communication among vehicles, contributing to advancements in intelligent transportation systems. However, VANETs face significant security and privacy challenges that must be addressed to ensure their widespread adoption. This research examines the threats encountered in VANETs, such as Sybil attacks, Denial of Service (DoS) attacks, data privacy breaches, location privacy concerns, message authentication issues, misbehaving nodes, and physical attacks. To mitigate these threats, various countermeasures are discussed, including public key infrastructure, intrusion detection systems, encryption techniques, pseudonym changing, reputation-based mechanisms, and physical security measures. Nonetheless, the dynamic nature of VANETs necessitates ongoing research and development to address emerging challenges and identify novel solutions. Future directions in this field involve exploring advanced cryptographic algorithms, machine learning-based anomaly detection techniques, and collaborative approaches among vehicles to enhance security and privacy in VANETs. The findings of this research contribute to the understanding of security and privacy challenges in VANETs and provide valuable insights for researchers, practitioners, and policymakers working towards secure and privacy-preserving vehicular communication systems.
... Although vehicular ad-hoc network (VANET) is not a new subject, it gives a new research challenges and problems. The main goal of VANET is to help a group of vehicles to communicate to each other without controller or any other infrastructure [1]. Autonomous vehicle (AV) technology offers the possibility of fundamentally changing transportation. ...
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Vehicular ad-hoc network (VANET) is a technique that uses cars moved in cities or highways as nodes in wireless networks. Each car in these networks works as a router and allows cars in the range to communicate with each other. As a result of this movement, some cars will become out of range, but these networks can connect to the internet and the cars in these networks can connect to each other. This research proposes a unique clustering strategy to improve the performance of these networks by making their clusters more stable. One of the biggest problems these networks face is traffic data, which consumes network resources. Agent based modeling (ABM) evaluates better networks. The evaluation showed that the proposed strategy surpasses earlier techniques in reachability and throughput, but ad hoc on-demand distance vector (AODV) (on-demand/reactive) outperforms it in total traffic received since our hybrid approach needs more traffic than AODV.
Conference Paper
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Spatial Aloha is probably the simplest medium access protocol to be used in a large mobile ad hoc network: each station tosses a coin independently of everything else and accesses the channel if it gets heads. In a network where stations are randomly and homogeneously located in the Euclidean plane, there is a way to tune the bias of the coin so as to obtain the best possible compromise between spatial reuse and per transmitter throughput. This paper shows how to address this questions using stochastic geometry and more precisely Poisson shot noise field theory. The theory that is developed is fully computational and leads to new closed form expressions for various kinds of spatial averages (like e.g. outage, throughput or transport). It also allows one to derive general scaling laws that hold for general fading assumptions. We exemplify its flexibility by analyzing a natural variant of Spatial Aloha that we call Opportunistic Aloha and that consists in replacing the coin tossing by an evaluation of the quality of the channel of each station to its receiver and a selection of the stations with good channels (e.g. fading) conditions. We show how to adapt the general machinery to this variant and how to optimize and implement it. We show that when properly tuned, Opportunistic Aloha very significantly outperforms Spatial Aloha, with e.g. a mean throughput per unit area twice higher for Rayleigh fading scenarios with typical parameters.
This book provides an invaluable introduction to inter-vehicular communications, demonstrating the networking and communication technologies for reducing fatalities, improving transportation efficiency, and minimising environmental impact. This book addresses the applications and technical aspects of radio-based vehicle-to-vehicle and vehicle-to-infrastructure communication that can be established by short- and medium range communication based on wireless local area network technology (primarily IEEE 802.11). It contains a coherent treatment of the important topics and technologies contributed by leading experts in the field, covering the potential applications for and their requirements on the communications system. The authors cover physical and medium access control layer issues with focus on IEEE 802.11-based systems, and show how many of the applications benefit when information is efficiently disseminated, and the techniques that provide attractive data aggregation (also includes design of the corresponding middleware). The book also considers issues such as IT-security (means and fundamental trade-off between security and privacy), current standardization activities such as IEEE 802.11p, and the IEEE 1609 standard series. Key Features: Covers the state-of-the-art in the field of vehicular inter-networks such as safety and efficiency applications, physical and medium access control layer issues, middleware, and security Shows how vehicular networks differ from other mobile networks and illustrates the idea of vehicle-to-vehicle communications with application scenarios and with current proofs of concept worldwide Addresses current standardization activities such as IEEE 802.11p and the IEEE 1609 standard series Offers a chapter on mobility models and their use for simulation of vehicular inter-networks. Provides a coherent treatment of the important topics and technologies contributed by leading academic and industry experts in the field. This book provides a reference for professional automotive technologists (OEMS and suppliers), professionals in the area of Intelligent Transportation Systems, and researchers attracted to the field of wireless vehicular communications. Third and fourth year undergraduate and graduate students will also find this book of interest.
The chapter provides a survey of routing protocols in vehicular ad hoc networks. The routing protocols fall into two major categories of topology-based and position-based routing. The chapter discusses the advantages and disadvantages of these routing protocols, explores the motivation behind their design and trace the evolution of these routing protocols. Finally, it concludes the chapter by pointing out some open issues and possible direction of future research related to VANET routing.
In recent years, thanks to the development and popularization of wireless network technologies, the issue of vehicular ad hoc network (VANET) has received great attention, and more and more VANET-related researches have been brought up. Generally speaking, the biggest difference between VANET and traditional ad hoc network is the velocity of carriers because in VANET, the velocity of vehicles, the carriers, is much higher than those in traditional ad hoc. Therefore, it would be a great challenge to forward data efficiently in VANETs and many researches proposed have focused on the development of routing protocols. The current proposed routing protocols are all assumed to simulate in a distributed and ideal environment. As for the complex geographic environments, such as urban scenarios, extra amendments must be needed to improve the efficiency of the routing protocols. Thus, the main purpose of this paper is to design a suitable routing protocol for urban scenarios with better performance and adaptability. For this reason, greedy on straight roads and predictive at the intersections (GSPI) routing protocol is proposed to use greedy mode on straight roads and to use predictive mode at the intersections. In greedy mode, we choose the next hop according to the weight value that combines the distances and multi-rate. In predictive mode, we predict the directions of the vehicles to determine the next hop. The simulation results reveal that our proposed algorithm indeed proves its feasibility. Copyright © 2010 John Wiley & Sons, Ltd.
Conference Paper
Owing to the features of erratic speeds and varying topography and requirements of minimum delay and high application reliability in terms of data delivery and security, existing MANET routing protocols prove to be inefficient in VANETs. In acknowledgment to the requirement for new VANET protocols addressing issues of routing, data dissemination, data sharing and security, this paper proposes a novel geographic routing technique called GROOV, which takes into account varying topographies and densities of highways as well as cities. To increase reliability, GROOV calculates transmission feasibility for each node, based on link quality (average acceleration), range weight (weightage to relative positions of nodes) and direction, instead of traditional greedy forwarding, in the selection of the next relay node. Taking volatility of critical city intersection scenarios into account, GROOV calculates new node coordinates of vehicles at intersections to make best route selections at intersections and thus, routes the data packet through the path directed at the intended recipient. This prevents the occurrence of a routing loop, thereby, decreasing delay and increasing packet delivery ratio. Simulation results show that GROOV achieves a high level of routing performance in terms of packet delivery ratio, end-to-end delay and average number of hops in both city straight road/highway and city intersection scenarios.
Conference Paper
The paper presents the Vehicular Ad hoc Networks and the typical routing protocol: the ad hoc on-demand routing protocol (AODV) in mobile ad hoc networks and the optimized protocol AODV_OBD for protocol AODV; also presents a practical mobility model that enable the simulation experiment more veritable. Then it use network simulation tool(ns2) to simulate the two routing protocols in ad hoc networks based on Linux and then compares and analyses the simulation results and do performance evolution. We can infer that AODV_OBD routing protocol induces the packet delay to a certain extent compared with AODV routing protocol.
An extensive update to a classic text Stochastic geometry and spatial statistics play a fundamental role in many modern branches of physics, materials sciences, engineering, biology and environmental sciences. They offer successful models for the description of random two- and three-dimensional micro and macro structures and statistical methods for their analysis. The previous edition of this book has served as the key reference in its field for over 18 years and is regarded as the best treatment of the subject of stochastic geometry, both as a subject with vital applications to spatial statistics and as a very interesting field of mathematics in its own right. This edition: presents a wealth of models for spatial patterns and related statistical methods; provides a great survey of the modern theory of random tessellations, including many new models that became tractable only in the last few years; includes new sections on random networks and random graphs to review the recent ever growing interest in these areas; provides an excellent introduction to theory and modelling of point processes, which covers some very latest developments; illustrate the forefront theory of random sets, with many applications; adds new results to the discussion of fibre and surface processes; offers an updated collection of useful stereological methods; includes 700 new references; is written in an accessible style enabling non-mathematicians to benefit from this book; provides a companion website hosting information on recent developments in the field Stochastic Geometry and its Applications is ideally suited for researchers in physics, materials science, biology and ecological sciences as well as mathematicians and statisticians. It should also serve as a valuable introduction to the subject for students of mathematics and statistics.
In the last years many routing protocols proposals have been made considering the particular VANET characteristics. From the many proposals that came up, the protocols based on the vehicles positions were found to be the most adequate to VANETs due to their resilience to handling the nodes position variation. In this study we will survey the existing position-based routing protocols. Unlike other studies we will emphasise on their applicability to different environments. We start by characterising the vehicular network environment, namely the urban and the highway environments. Afterwards, topology-based protocols are compared to position-based protocols and to the latter are identified the different used strategies and their performances are qualitatively evaluated relatively to different metrics. The different position-based routing proposals are described including a pseudo-code specification, and a comparison is made based on different perspectives. To conclude, the main constrains to urban and highway environments are characterised and the adaptability of each protocol to each of the environments is evaluated.