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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 4, April (2014), pp. 247-256 © IAEME
247
NETWORK CODING BASED MULTICAST FOR VANET
Jitendra Bhatia
1
, Zunnun Narmawala
2
1
Assistant Professor, CSE Department, Institute of Technology, Nirma University,
Ahmedabad - 382 481, Gujarat, India.
2
Assistant Professor, CSE Department, Institute of Technology, Nirma University,
Ahmedabad - 382 481, Gujarat, India.
ABSTRACT
A Vehicular Ad-Hoc Network, or VANET, is a delay Tolerant network in which no
contemporaneous path exists between source and destination most of the time. So, routing protocols
proposed for VANET follow ‘store-carry-forward’ paradigm in which two nodes exchange messages
with each other only when they come into contact. Multicast can be used to perform the regional
multicasting to deliver safety related, commercials and advertisements messages. The challenging
problem in multicasting is how to deliver packets to all the nodes within the particular region with
high efficiency but low overhead. Network coding with Multi-Generation-Mixing is a special in-
network data-processing technique that can potentially increase the network capacity and packet
throughput in wireless networking environments. In this paper, a network coding with MGM based
Multicast algorithm for transmitting multicast packets over VANET is proposed. The proposed
algorithm can increase packet delivered ratio at each mobile node. As a result, the safety and
transmission efficiency can be achieved simultaneously. We developed multi-copy routing protocol
for multicasting in VANET which uses ‘Network coding with MGM’ to reduce this overhead.
Simulation results shows that proposed multicasting protocol outperforms the conventional network
coding based protocol in terms of throughput and delay
Key words: Network Coding, Vanet, Multicasting.
1. INTRODUCTION
Network coding is considered as a generalization of conventional store and forward
techniques and it’s a tool for optimization which can improve the chances of delivery in a
spontaneous network, and also it was originally proposed in order to achieve multicast data delivery
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING
AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 4, April (2014), pp. 247-256
© IAEME: www.iaeme.com/ijaret.asp
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at the maximum data transfer in single source multicast [1].Network coding need to use algebraic
nature of data. There are three well known application of network coding in overlay networks:
distributed storage system, content distribution and layered multicast. There are two types of
network coding, Deterministic Linear Network Coding (LNC) and Random Linear Network
Coding (RLNC). In traditional network, relay node or router simply forward the information
packets destined to other node. In LNC, source node or intermediate node or router allows to
combine number of packets it has received or generated into one or several outgoing packets. With
linear network coding, outgoing packets are linear combinations of the original packets, where
addition and multiplication are performed over the field GF2
s
[2]. Linear combination is not
concatenation, if we linearly combine packets of length L, the resulting encoded packet also has
size L.
The rest of the paper is organized as follows. Section 2 describes the working of MGM. In
section 4, a new network coding with MGM based multicast algorithm for VANET is presented.
Section 7 demonstrates the simulation scenario provides results and analysis. Finally, in section 8
some concluding remarks and scope for future work is presented.
2. NETWORK CODING WITH MULTI GENERATION MIXING(MGM)
Network Coding with Multi-generation mixing (MGM) is a RLNC approach which improves
the performance without increasing buffer size. In MGM mixing set of size m generations can be
coded together. A new set of generation packet is mixed with previously transmitted generations.
Results show that MGM reduces overhead for are covery of packets. In MGM, N packets are
grouped into generations where the size of each generation is k packets. Each generation is assigned
a sequence number from 0 to N/k. In G-by-G Network coding encoding is allowed amongst packet
belonging to the one generation. While in MGM generations are grouped into mixing sets where the
size of mixing set is m generations. Each mixing set has an index M. Generation i belongs to mixing
set with index M=i/m. Each generation in mixing set has a position index. Position index (l) of
generation i in a mixing set of size m is i mod m. G-by-G Network coding is a special case of MGM
where m=1. In MGM packets of different generations are encoded together. When node sends a
packet belonging to generation i with position index l in mixing set, that node encode all packets that
are associated with the generations of same mixing set and have the position indices less than or
equal to l as shown in Figure 1[3]. Size of encoding vector depends on the number of packets
encoded together at sender node. Number of packets that are encoded together depends on the
position index of the generation with which packet is associated. Packet in generation with position
index l have the size of encoding vector is (l+1)k. So sender will generate (l+1)k independent
packets. In Network Coding with MGM goal is to enhance decodable rates in situation where losses
prevent efficient propagation of sender packets. MGM allows the cooperative decoding among the
different generations of a mixing set which enhances decodablity. Compare to G-by-G Network
coding with MGM extra encoded packets associated with generation protect more than one
generation. Computation overhead is incurred at intermediate node to check the usefulness of
received packets and at receiver node to decode received packets[4]. In g-by-g Network coding
computation are performed on packets within the generation so it is fixed due to fixed generation
size. But in MGM encoding/decoding is performed on packets belonging to at least one generation in
mixing set and so computational overhead is not fixed. In MGM in case generation is unrecoverable
due to the reception of insufficient encodings, it is still possible to recover that generation
collectively as a subset of mixing set generations. Packets received with generation of higher
position indices have information from generations of lower position indices and hence contribute in
recovery of unrecovered generations of lower position indices in the same mixing set. Redundant
encoded packets enhance the reliability of communication. With MGM extra packets protects all

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generations with lower position indices. While inG-by-G Network coding extra packets protects that
generation only.
Figure 1: Network Coding with MGM, each generation is encoded with previous generations in
mixing set[3]
In MGM there are different options for sending extra packets. One option is distribute the
packets over all generations of mixing set. Another option is to send extra encodings with the last
generation of mixing set. So, extra encodings protects all mixing set generations.
Figure 2: Generation’s partitioning with MGM into different layers of priority. Mixing set size is m,
generation size is k[5]
3. MULTICASTING IN VANET
Many VANET applications need multicast service. For example, vehicle on road may send
the packet regarding accident to one of the server(ambulance or emergency service providers).
However, conventional multicast methods proposed for ad hoc networks are not suitable for
VANET, due to frequently disconnectivity in the network. Data transmissions suffer from large end-
to-end delays along the tree because of the repeated partitions due to frequent disconnections. Also
the conventional approaches may fail to deliver a message when the possibility of link unavailability
becomes high.
3.1 Multicasting in wireless networks
Network coding is potentially applicable to many forms of network communications. Up to
now, the best understood scenario where network coding offers unique advantages is multicasting in
a wireless communication network.

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Throughput enhancement is one of the application of network coding to wireless networks.
Wireless networks are suitable for network coding because wireless links inherently have the
broadcast nature. Network coding scheme for multi-hop wireless networks improves throughput
performance with the following simple example shown in figure. [6]. Network coding could be more
helpful for improve delay, reliability and robustness, rather than improving throughput enhancement
only for multicasting.
3.2 Characteristics of VANET Scenarios
Nodes move at very high speed. Highly dynamic topology. Vehicles are equipped with long
lived batteries, so the energy consumption due to communication is negligible. Mobility patterns are
constrained. Vehicle can have digital maps of the geographic zone they are travelling around.
Positioning information may be acquired via geographic positioning system like GPS or Galileo. [7]
Interaction with onboard sensors.
3.3 Common services used for VANET
• Safety information
• Advanced driver assistance systems
• Traffic management
• Infotainment
3.4 ISSUES
Due to the unpredictability of network connectivity and delay, and limited buffer,
Multicasting in VANETs is a quite unique and challenging problem. It requires both re-definition of
Multicasting semantics and new routing algorithms. But these approaches cannot be applicable to
VANETs since for Multicasting routing it cannot assume the connectivity is guaranteed, and the
uncertainty of both the path to a destination group member and the destination of the Multicasting
message during the routing makes the problem more challenging. One of the challenges in designing
a Multicasting routing protocol is to maintain the group membership efficiently. Due to the long
delivery delay in VANETs, group membership may already change during the delivery of a message,
introducing ambiguity in Multicasting semantics.
4. THE PROPOSED PROTOCOL
Procedure mgm_processing(node Id)
1. if Id = Source_node then
(a) Create n generations of k packets in to each mixing set m
(b) Encode the generation using multi-generation mixing concept for each mixing set.
(c) send the packets
2. if Id = Intermediate_node then
(a) Calculate the rank of received packets for each generation of particular mixing set
(b) if the rank of received packets is sufficient then do collectively decoding
(i.e. generation size*generation ID)
else
"decoding not possible" and wait for new node to become neighbor

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(c) Do re-encoding of the received packets.
(d) Send the encoded packets with their respective effective co-efficient vector to its neighbor
nodes.
3. if Id = Destination_node then
(a) Calculate the rank of received packets foreach generation of particular mixing set
(b) Decode it if rank is sufficient
i.e. rank>=gen_size * gen_ID
(c) send anti-packets to its neighboring nodes
End Procedure
5. OVERVIEW
5.1 Opportunistic Routing
VANET, which is Delay Tolerant Networks or Intermittently Connected Networks in which
end-to-end connectivity is not present most of the time. In such a network, conventional approach of
finding route or source-rooted multicast tree before data transmission is not feasible. So, in our
protocol, data transfer takes place whenever two nodes come into communication range of each
other.
5.2 MultiCopy Scheme
We assume that no prior information about the network to pology or connection pattern is
available, as it is the case in mobile ad hoc networks most of the time. Single copy schemes generally
rely heavily on such information and these schemes have very high delivery delay and low delivery
ratio. Further, Multi-copy schemes are very robust. So, we choose our protocol to be a Multi-copy
protocol
5.3 Network coding
In existing routing schemes for VANET, whenever a transmission opportunity arrives,
ideally, a node should forward packets such that the destination node gets all the required packets
without getting any redundant packet. However, a forwarding node has no such precise knowledge in
VANET. So, it is difficult to select the best suitable packet for transmission. On the other hand, in
the network coding based protocol, a node can transmit any of the coded packets since all of them
can contribute the same to the eventual delivery of all data packets to the destination with high
probability. Similarly, the network coding based protocol has the advantage in proper utilizing
limited buffer resource since dropping any coded packet has the same effect. So, our protocol uses
network coding to exploit these and other benefits mentioned earlier.
5.4 Purging Scheme
For efficient buffer usage, copies of already delivered packets have to be purged from the
nodes in the network.
5.5 Estimation of Protocol Parameters
Following are the two configurable parameters in our protocol: 1. Generation size (G): It
denotes the size of the generation. For the reasons explained earlier, packets are grouped into
generations and only the packets in the same generation can be mixed. 2. Mixing set size (MSS): It
denotes the number of generations of size G in particular mixing set.

252
The network parameter of interest is Meeting rate. Of the network is the average number of
times a node meets with any other node in the network per second. It depends on the area within
which the network nodes move (field area), their velocities and communication range and the
mobility pattern.
6. PROTOCOL DESCRIPTION
In this section, we describe working of our protocol. Data packets are grouped into
generations. Nodes store independent packets along with their coefficients according to RLC
scheme.
Main components of our protocol are explained in following sections.
Figure 3: Diagram representing protocol components
6.1 Neighbor Management
Every node in the network transmits ‘HELLO’ packet at fixed interval called as ‘HELLO
Timer’. Duration of the interval is pre-configured parameter which is decided depending on speed of
the nodes and their communication range. e.g., if we consider the case of neighbour nodes moving
with 6 m/s speed in opposite directions having communication range of 100 m, they will remain in
contact for approximately 34 seconds. If we keep the HELLO Timer value to be 10 seconds, the
neighbour node will be detected at most after 10 seconds from the actual time of first contact
between two nodes and the node will not be able to make use of approximately 1/3rd of total contact
period. If we decrease HELLO Timer value, then number of HELLO packets in the network will
increase but neighbour will be detected early. So there is a tradeoff. Whenever a node receives
HELLO packet from another node, it adds that node into its neighbour list if that node is not in the
list already. If any node does not receive any HELLO packet for the interval equal to three times
‘HELLO Timer’ from its neighbour node, that node is purged from the neighbour list. This interval is
called as ‘Neighbour Purge Timer’.
6.2 Purging
After adding a node into the neighbour list, the node shares accumulated delivery information
with its neighbour for purging. Apart from these schemes, remaining packets of generation are
purged from all the buffers after a timeout period ‘TTL’. This timeout mechanism ensures that, if a
generation is not delivered to all the destinations or delivery information from all destinations are not

253
received by a node even after TTL delay, it will be purged. So value of TTL is to be kept sufficiently
large such that generations are received by most of the destinations most of the time.
6.3 Packet Mixing and Forwarding
After intelligent beaconing, the initiator node sends encoded data packets to the neighbour till
it is within communication range. The generation of which next encoded packet is to be forwarded,
along with its coefficients, is decided based on some forwarding policy
6.4 Packet Reception
When the neighbour node receives the packet and the buffer is full, it makes room in the
buffer as per the buffer management policy mentioned below and it stores the coefficients of the
packet in the corresponding coefficient matrix
6.5 Packet Decoding
When the sufficient number of packets from all the generation of particular mixing set at the
destination node is equal to (mixing set size * generation size)
7. SIMULATION
We have simulated the proposed protocol in NS2 simulator and The network contains 50
wireless nodes which move according to mobility models generated by MOVE simulator. The
minimum speed of a node is 10 m/s. The communication range of a node is 100 m and band width of
the channel is 1 Mbps. Meeting rate (γ) is changed by varying field area of the network. There is
source in the network and there are different number of destinations i.e. Group Size. For network
coding, randomly chosen coefficients and addition and multiplication operations for encoding and
decoding are over the Galois field F2
8
.
7.1 Simulation Results
Our performance parameter of interest is percentile delay(δ) which we define as time taken to
deliver given percentage of total packets by the network. Please note that it captures two
performance parameters namely delivery ratio and delivery delay. The protocol parameters are
generation size (G) and number of generations in one mixing set (MSS). The network parameter of
interest is meeting rate (γ).
7.2 Infinite Buffer Case
In this section, we present the performance of the protocol when buffers are infinite. i.e., each
node has enough buffer to store all the generations of each mixing set from all sources. Once average
speed of the nodes in the network achieves steady state, all the source nodes generate given number
of data packets which are grouped into generations for a particular mixing set i.e., data packets are
generated in a pulse and there is no new traffic generated after that.
For the results shown, number of data packets per source are 64. We run the simulation for
sufficient time period such that all the generations of particular mixing set are received by all
intended destination nodes. For infinite buffer case, anti-packets are generated only when all
generations of particular mixing set is delivered. A node purges entire generation when the node has
accumulated all the destinations in its destination list for that generation of particular mixing set. We
observe from Fig. 4, that as we increases the meeting rate block delivery delay(δ) will decreases
because as more and more number of nodes comes in contact chances of delivery is going to be
increase but it will increases the redundancy also. For the value of γ = between 0.8 and 0.9,

254
decreasing in value of δ is almost nearer, but for lower value of γ, MGM outperforms in delivery
delay.
As shown in Fig. 5, as mixing set size increases delay decreases. For decoding entire mixing
set we need sufficient rank i.e. sufficient number of packets to decode particular mixing set. for
example in our MGM case G=8 and MSS=8 so total number of packets are 64 but after applying
MGM based network coding, we will have 288 packets out of which if we get total number of 64
packets from different generation of that mixing set then destination node is able to decode all the
packets as rank is sufficient. Note rank indicates the sufficient innovative packets to decode entire
generation/Mixing set. Our result implies that if we increase our mixing set up to some extent it will
out performs in case of delay over conventional and G-by-G scheme. For conventional scheme i.e.
MSS=1 and G=1 Delay is higher with compare to the case where MSS=1 for different value of G= 2,
4 and 8 but for MGM case where MSS=8 and G=8, δ decreases drastically.
Figure 4: Delay v/s Meeting rate Figure 6: Packet delivery ratio v/s Mixing set size
Figure 5: Delay v/s Mixing set size Figure 7: Packet delivery ratio v/s Meeting rate
As shown in Fig. 6, packet delivery ratio increases, as we increase the mixing set size for
meeting rate (γ =0.43). For conventional scheme, it is less with compare to G-by-G case (i.e. MSS=1
and G=2, 4, 8). MGM case where MSS=8 and G=8 have higher value of α.
As shown in Fig. 7, value of α increases as γ increases. MGM outperforms over conventional
and G-by-G scheme for lower values of γ but it become somewhat stable after γ=0.73.
From Fig.8, it is clear that number total number of packets received increases as time goes
on. MGM out performs over both the scheme.

255
Figure 8: Throughput v/s Time
8. CONCLUSION AND FUTURE SCOPE
VANET which is an example of Delay Tolerant Networks require different routing strategy
than conventional networks because of frequent and long partitions in the network. To improve
chances of delivery, Single or Multicopy schemes are used. However, communication overhead and
buffer occupancy increases as we increase number copies per packet. To reduce this overhead
without impacting performance, we use network coding based single-copy scheme.
9. FUTURE WORK
We will work on multi-copy approach that will generate redundant copies of the same packet
for increasing the probability of delivery for finite buffer with probabilistic purging mechanism to
utilize optimal use of buffer which takes advantage of network coding and also binary spray and wait
[8] mechanism to reduce the number of copies in the network for optimal usage of buffer and
bandwidth. We will work on cross layer optimization in which speed and direction parameters from
physical layer can be used at network layer for intelligent routing.
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