An adaptive broadcast mechanism to improve alert

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 03 Issue: 05 | May-2014, Available @ http://www.ijret.org 20
AN ADAPTIVE BROADCAST MECHANISM TO IMPROVE ALERT
MESSAGE DISSEMINATION IN VANETS
Nidhin A S1
, Vinaya K2
1
PG Scholar, Computer Science & Engineering Department, KCG College of Technology, Chennai, India
2
PG Scholar, Computer Science & Engineering Department, KCG College of Technology, Chennai, India
Abstract
VANET is a rapidly emerging research field and is essential for cooperative driving on the road. VANET technology uses moving car
as nodes in a network to create a mobile network. The number of vehicles has been increased on road in the past few years. Due to
high density of vehicles, road accident and the potential threats on the road is increasing. VANET is aiming to equip technology in
vehicles to reduce these factors by disseminating messages to each other. Warning messages have to be quickly disseminated in order
to reach maximum number of vehicles on road. Adapting to the environment where the vehicle is moving is essential to improve the
warning message dissemination when an abnormal situation occurs on the road. The notification to the nearby vehicle is done by
simply broadcasting the messages which is retransmitted over and again by the vehicles simultaneously to other nearby vehicles. Due
to this retransmission of warning message it leads to problem namely broadcast storm problem. This work proposed an adaptive
broadcast message forwarding process to improve the warning message dissemination in real urban scenarios and predict the
reduction in severity of broadcast storm problem. The efficiency of the alert dissemination can be increased if the vehicles determine
the city profile of their current area.
Keywords— Adaptive mechanism, alert dissemination, broadcast storm problem, roadmap scenarios, Mobility Models,
VANET.
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1. INTRODUCTION
Vehicular Ad hoc Networks (VANETs) are a special case of
Mobile Ad Hoc Networks (MANETs) wherein the nodes are
modeled as vehicles. These nodes are capable of
communicating with each other on an adhoc basis, without a
fixed Infrastructure. VANET considers each participating
node as a router thus enabling the nodes to connect to each
other and transfer the data, thus creating a network. VANET is
a subclass of Intelligent Transportation System (ITS) in order
to provide safety and comfort to the road users. The major
applications of VANET includes safe driving, co-operative
driving, traffic optimization. Since vehicle is moving on the
road, vehicles make connection with another vehicle that may
never met before. This connection lasts for only few seconds
since the vehicle is moving in its own direction, and never
meets again in the network. These connections will be lost as
each car has a high mobility and may be travel in opposite
direction. Mobility pattern of vehicles depends on traffic
environment, road structure, speed of vehicles, driver’s
behavior and so on. Currently vehicles have become the main
transportation tools, and VANETs has become a hot research
topic for more and more researchers begin to realize the
potential perspective of the vehicle network. This work mainly
focusing about the data dissemination in VANETs and try to
propose a message dissemination algorithm for the
applications which are emerging for VANETs
Adapting to the environment where the vehicle is moving is
essential to improve the warning message dissemination and
to reduce the broadcast storm problem. This work mainly
focus on traffic safety and efficient warning message
dissemination, where main goal is to increase the accuracy of
the information received by the nearby vehicles when a
abnormal situation occurs. Existing techniques for VANET
usually considers vehicles in the road such as their density,
speed and position. Most of the works related to VANET in
the literature mainly focus on end-to-end routing in highway
scenarios. These techniques are not suitable to warn highest
number of vehicles when an abnormal situation occurs in
realistic vehicular traffic environment. In the past, a lot of
techniques have been proposed to enhance the warning
message dissemination but none of them is tested in real urban
scenarios. New proposal for warning message dissemination
in real urban scenario is needed which should consider both
the number of vehicles in the environment and the road
topology information.
This work proposed traffic safety and efficient message
dissemination for reducing the latency and to increase the
accuracy of the warning message dissemination received by
nearby vehicles when a dangerous situation occurs Manuel
[3]. An algorithm called PAWDS, Profile-driven adaptive
Warning message Dissemination System is proposed which
dynamically modifies some of the key parameters of the alert

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dissemination process to enhance the efficiency of the warning
message dissemination and reducing the broadcast storm
problem by considering city profile. In VANET, any vehicle
detecting an abnormal situation should notify the anomaly to
nearby vehicles that could face this problem in a short period
of time. Hence a simple broadcasting increases the number of
messages in the network over time. Simultaneous forwarding
of messages without any condition will cause message
redundancy, contention and massive packet collisions [8].
Such a situation must be avoided or reduced.
The rest of the paper is organized as follows. Section II
presents several broadcast storm reduction techniques and
adaptive forwarding mechanisms related to the work. Section
III justifies the necessity of city profile information and their
classification. Section IV describes the implementation of
algorithm and checks the effects of broadcast storm problem.
In Section V presents and analyze the obtained results. Finally,
Section VII concludes the paper.
2. BACKGROUND AND RELATED WORK
In the networking literature, there are several works that
proposed either broadcast storm reduction techniques or
adaptive mechanisms to enhance message dissemination. The
following section deals with most representative work related
to proposed work.
2.1 Broadcast Storm Mitigation Techniques
There are various techniques by which a message could be
disseminated over the network. In the networking literature,
there are several works that proposed to reduce the broadcast
storm problem and adaptive mechanism to enhance the
efficiency of the alert dissemination. The following literature
review deals with the literature works related to this project.
The Counter-based scheme [8] uses a threshold C and a
counter c to keep track of the number of times the broadcast
message is received. Whenever c ≥ C, message rebroadcast is
inhibited. The Distance-based scheme [8] use the relative
distance d between vehicles to decide whether to rebroadcast
or not. When the distance d between two vehicles is short and
the additional coverage (AC) of the node is lower,
rebroadcasting the warning message is inhibited. If d is larger,
the additional coverage will also be larger. The Location-
based scheme [8] requiring more accurate locations for the
broadcasting vehicles need an accurate geometrical estimation
(with convex polygons) of the AC of a warning message.
Since vehicles usually have GPS systems on-board, it is
possible to estimate the additional coverage more accurately.
The other rebroadcast schemes for VANET is slotted 1-
persistence, slotted p-persistence and weighted p-persistence
[9]. These three probabilistic and timer-based broadcast
suppression techniques are not designed to solve the broadcast
storm problem, but they can reduce the severity of the
broadcast storm by allowing only nodes with higher priority to
access the channel as fast as possible. These schemes are
specifically designed for use in highway scenarios.
The Last One (TLO) scheme [6] technique reduce the
broadcast storm problem by finding the most distant vehicle
from the warning message sender node, this vehicle will be the
only allowed node to retransmit the message in network. This
method uses GPS information from the sender vehicle and the
possible receivers to calculate the distance. GPS information
must be accurate to achieve good results, and it is not correctly
specified how a node knows the position of its nearby vehicles
at any given time.
Enhanced Street Broadcast Reduction (eSBR) scheme [6]
uses two types of message for communication between the
vehicles namely, warning message, informing about an
emergency situation and beacon message, informing about the
position, speed etc. of the vehicle. The message is
rebroadcasted after a fixed time interval if the distance
between the sender and receiver is greater than the initialized
rebroadcast distance. The message ID is stored in the vehicle
database, if the same message is received again, by comparing
it with already existent ID the message is discarded and is not
forwarded again by the vehicle.
The Cross Layer Broadcast Protocol (CLBP) [1] uses
geographical locations and velocities of vehicles to select the
forwarding vehicles efficiently. This scheme uses Broadcast
Request To Send (BRTS) and Broadcast Clear To Send
(BCTS) frames exchanging for reliable transmissions. This
scheme focus on single-direction environment like highway
scenarios and its performance has not been tested in urban
scenarios.
2.2 Adaptive Scheme for Message Dissemination
In VANET research works are less for message dissemination.
Backfire Algorithm [4] proposed for improving the message
dissemination. Vehicles calculates the density of neighbor
vehicles to decide whether to forward or not. An opportunistic
auto adaptive dissemination scheme proposed [2] - Adaptive
Copy and Spread (ACS) Algorithm - for VANETs, this
technique dynamically adjusts the dissemination strategies
based on the moving patterns of vehicles such as direction
and velocity,. This proposed scheme automatically increases
or decreases the number of message replicas inside the
broadcast area, and vehicles can decide when to start or stop
broadcast a message. Adaptive spread and copy is designed to
keep the message at the effective area's boundary for
informing this situation when the vehicle entering as soon as
possible.
In summary, VANET have many protocols but most of them
are available for one direction scenarios or end-to-end routing.
Some protocols are designed for the highway scenarios such

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as only one direction of prorogation is considered. Achieving
efficient warning message broadcast is of utmost importance
in vehicular networks to warn other vehicle of real time traffic
information. To overcome these drawbacks, this work mainly
focus on improving the efficiency of the warning message
broadcast while reducing the number of messages in the
vehicular communication network and improve the accuracy
of information received by nearby vehicles.
3. IMPACT OF ROADMAP TOPOLOGY
One of the most important issues in the protocol design of
VANET is absence of existing mobility model for imitating
the realistic behavior of vehicular traffic [5]. Roadmap has an
important influence in the message dissemination since
topology constrains car movement. In order to reduce the
broadcast storm problem messages are transmitted based on
the road topology. Road topology is classified into three
according to the number of streets and junctions in the city.
They are Simple layout (low density of streets and junctions),
Regular layout (medium density of streets and junctions) and
Complex layout (high density of streets and junctions). There
are three message dissemination schemes are used based on
the city profile information. They are Full dissemination,
Standard dissemination and Reduced dissemination.
Full dissemination: When the vehicles move in a low density
area then vehicles can send as many message as possible since
the vehicles in the city are less.
Standard dissemination: Density of vehicles in the city is
medium vehicle should maintain balance between number of
messages send and number of messages received.
Reduced dissemination: Vehicles send as few messages as
possible because the vehicles move in a high density area.
4. IMPLEMENTATION OF ALGORITHM
Each vehicle is equipped with GPS and city profile is
identified by using onboard GPS system. There are two types
of messages namely, warning messages and beacon messages.
Warning messages are used to inform other vehicles about the
abnormal conditions on the road and beacon messages are
exchanged among the vehicle to inform about their speed,
position etc of the vehicles. Vehicle density is calculated by
exchanging the beacon signal among the nearby vehicles. City
profile identification and the density of vehicles on the road is
the basis for the algorithm implementation. The algorithm
efficiently selects the most suitable message dissemination
depending on the profile of the street map and the estimated
vehicle density.
The following Table 1 shows the parameters used in each
working modes in the algorithm and T is the time taken to
reconfigure the system. The effectiveness of the alert
dissemination can be increased if the vehicles determine their
city profile of their current area and adapting to the
environment by selecting the appropriate dissemination
scheme accordingly. Table specifies different broadcast
schemes used in different working modes and interval
between the message broadcast in each dissemination scheme
.Most of the previous algorithm for VANET using a
predefined set of values. In this work the existing algorithm
automatically tune the parameters to enhance the warning
message and select the efficient mode of operation for sending
the message based on the city profile information and the
estimated density of vehicle on the road. Adapting to the
environment where the vehicle located is taken into account
for the message dissemination.
Table 1 Working Modes and Key Parameters
Working mode Interval
between
consecutive
messages
Broadcast
scheme
Min.
rebroadcast
distance
Full
dissemination
2 seconds Counter
based
--
Standard
dissemination
4 seconds eSBR 200m
Reduced
dissemination
5 seconds Distance
based
250m
The working and pseudo-code for the algorithm as shown
below
Algorithm 1: pseudo-code
Use standard dissemination scheme
While (1) do
obtain street map using GPS
Estimate the vehicle density using beacon message
if (city-profile is simple) then
if(vehicle density>25/km2
) then
use reduced dissemination scheme
else
use standard dissemination mode
else-if (city-profile is regular) then
) then
use standard dissemination scheme
else
use full dissemination scheme
else-if (city-profile is complex) then
) then
use standard dissemination scheme
else
use full dissemination scheme
sleep(T);

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5. SIMULATION AND PERFORMANCE
EVALUATION
Simulation result presented in this paper is done using Matlab
2010a. Since deploying and testing of VANET protocol is
costly in the real world without prior testing of protocol.
Simulation plays a vital role in imitating the realistic behavior
of vehicular traffic. Matlab is good for implementing the
algorithm accurately and provides mathematical proof for the
algorithm implementation. Matlab offers many predefined
mathematical functions for technical computing which
contains a large set of mathematical functions. This work
simulated with 200 vehicles in the roadmap scenario and result
shown in the figure 1.
Distance in meters
Fig.1 Implementation of Algorithm
In figure 1, the entire colored circle and the blank circle
represent the vehicle at an instant of time. Nodes are
represented with different color for better understanding of
results. Vehicle detecting abnormal condition is indicated in
the figure 1 as red thick node at the bottom left corner of the
scenario. When a vehicle detecting an abnormal condition it
has to inform other vehicle by using simple broadcasting.
Since each vehicle is equipped with GPS, selection of
broadcasting node is based on the position of node. Selection
of rebroadcasting node is based on the certain distance. The
red thick node selects the green node as the next forwarding
node. The green node again selects the yellow node as the next
forwarding node. Yellow node then selects red triangle node
as the next forwarding node but this node again selects the
green node as forwarding node. This selected green node was
previously the broadcasting node of red node. The red triangle
node then selects the blue triangle node for message
rebroadcast but some node selected was previously the
broadcasting node of another node. This blue triangle node
again selects read circle node as the next forwarding node. The
red circled node selected for rebroadcast was previously the
rebroadcasting node of some another node in the scenario.
This red circled node again selects the black triangle node for
message rebroadcast. But some of the node selected is
previously the rebroadcasting node of other vehicles. This
work shown that instead of selecting all the nodes in the
sender’s communication range for rebroadcast some of the
nodes are selected in the communication range. The broadcast
storm problem reduced efficiently but some of the nodes in the
sender’s communication range repeatedly act as the
rebroadcasting node.
Fig 2 Number of rebroadcasting nodes
Simulation results show that efficiency of alert dissemination
is increased and reduced the broadcast storm problem. But
some node again and again act as the rebroadcasting node of
some others as shown in figure.1.Selection of a set of
forwarding node for rebroadcasting is a challenge. About
42.50% of node has been selected for rebroadcast when
simulated with 200 vehicles in the scenario as sown in
figure.2. About 85 nodes act as the rebroadcasting node in the
scenario.
6. CONCLUSIONS AND FUTURE WORKS
This work outcome mobility model for VANET and improves
the warning message dissemination by considering dynamic
roadmap profiling. Based on the city profile information and
estimated vehicle density alert dissemination efficiency can be
improved. When the vehicle determine the city profile of their
current area where the vehicle is moving is necessary for
improving the alert dissemination process. Algorithm selects
adequate dissemination scheme based on the environment
Distanceinmeters

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dynamically. Simulation result shows that around 50% of
vehicle act as the rebroadcasting node when simulated with
200 vehicles. This work reduces the broadcast storm problem
but not completely reduced the problem because some nodes
again act as the rebroadcasting node and rebroadcast the same
messages in the network. This work proposes a non-geometric
broadcast approach for completely remove the broadcast storm
problem. In order to minimize communication area overlap
and maximize the broadcast coverage a virtual hexagonal
network is considered. GPS accuracy affects the
communication performance since GPS has about 50m to
100m of error bounds. Nodes that are closely located at the
boundary of sender’s communication range are selected for
rebroadcasting the message and to maximize the broadcast
coverage without using GPS.
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An adaptive broadcast mechanism to improve alert

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