A comprehensive survey of network coding in vehicular ad-hoc networks

Abstract

Network coding is a data processing technique in which the flow of digital data is optimized in a network by transmitting a composite of two or more messages to make the network more robust. Network coding has been used in traditional and emerging wireless networks to overcome the communications issues of these networks. It also plays an important role in the area of vehicular ad-hoc networks (VANETs) to meet the challenges like high mobility, rapidly changing topology, and intermittent connectivity. VANETs consist of network of vehicles in which they communicate with each other to ensure road safety, free flow of traffic, and ease of journey for the passengers. It is now considered to be the most valuable concept for improving efficiency and safety of future transportation. However, this field has a lot of challenges to deal with. This paper presents a comprehensive survey of network coding schemes in VANETs. We have classified different applications like content distribution, multimedia streaming, cooperative downloading, data dissemination, and summarized other key areas of VANETs in which network coding schemes are implemented. This research work will provide a clear understanding to the readers about how network coding is implemented in these schemes in VANETs to improve performance, reduce delay, and make the network more efficient.

Full text

A comprehensive survey of network coding in vehicular ad-hoc
networks
Farhan Jamil
1
•Anam Javaid
1
•Tariq Umer
1
•Mubashir Husain Rehmani
2
Springer Science+Business Media New York 2016
Abstract Network coding is a data processing technique in
which the flow of digital data is optimized in a network by
transmitting a composite of two or more messages to make
the network more robust. Network coding has been used in
traditional and emerging wireless networks to overcome the
communications issues of these networks. It also plays an
important role in the area of vehicular ad-hoc networks
(VANETs) to meet the challenges like high mobility, rapidly
changing topology, and intermittent connectivity. VANETs
consist of network of vehicles in which they communicate
with each other to ensure road safety, free flow of traffic, and
ease of journey for the passengers. It is now considered to be
the most valuable concept for improving efficiency and
safety of future transportation. However, this field has a lot
of challenges to deal with. This paper presents a compre-
hensive survey of network coding schemes in VANETs. We
have classified different applications like content distribu-
tion, multimedia streaming, cooperative downloading, data
dissemination, and summarized other key areas of VANETs
in which network coding schemes are implemented. This
research work will provide a clear understanding to the
readers about how network coding is implemented in these
schemes in VANETs to improve performance, reduce delay,
and make the network more efficient.
Keywords Vehicular ad-hoc networks Network coding 
VANETs Data dissemination Physical layer network
coding
1 Introduction
A decade ago researchers thought that the data communica-
tions can be made more efficient. If we send data in the form
of packets, which are scrambled in a completely random
fashion at one end, and descrambled at the other end in
communications network, instead of sending plain data.
Network coding was introduced with the concept to enhance
the throughput of the networks but now it is used to increase
the capacity, robustness, tomography, and security [1]. It was
first proposed by Ahlswede et al. [2] in which idea was given
that nodes in a network are allowed to encode information
received from input links. It has been in use in different
implementations of data communications networks like
Internet, wireless sensor networks (WSNs), peer to peer
networks, cognitive radio networks (CRNs), multicast net-
works, vehicular ad-hoc network (VANETs), and other
emerging networks. The higher acceptance of network cod-
ing in research community is primarily because, it improves
throughput, minimizes transmission rate, reduces energy
consumption, and minimizes energy per bit for multicasting
in wireless networks. It is used to provide neighbor discovery,
distributed storage, and secure transmission of data.
When thinking about the advancements in wireless
communications the researchers had contributed in many
aspects. The authors in [3] contributed in the ongoing
&Tariq Umer
t_umer@yahoo.com
Farhan Jamil
farhanjamil36@hotmail.com
Anam Javaid
anamjavaid1992@gmail.com
Mubashir Husain Rehmani
mshrehmani@gmail.com
1
Department of Computer Science, COMSATS Institute of
Information Technology, Wah Cantt, Pakistan
2
Department of Electrical Engineering, COMSATS Institute
of Information Technology, Wah Cantt, Pakistan
123
Wireless Netw
DOI 10.1007/s11276-016-1294-z

research by giving the brief survey about the security chal-
lenges in cognitive radio network, keeping in view all the
functional, operational and architectural aspects of CRNs.
The study also provides the strategies and future directions to
deal with these attacks. To give the overview on routing
protocols metrics applied in CRNs a comprehensive survey
is presented in [4]. the analysis on selection of routing
metrics and their behaviour under different routing condi-
tions is discussed in detail. The work on enhanced quality of
experience (QoE) in multimedia services by using optimized
channel allocation scheme in cognitive radio networks is
presented in [5]. The study gain the best utilization of
spectrum in CRNs communications for the multimedia
transmissions. The area of information centric network
(ICN) is focused by the researchers in [6]. The research work
covers all the research challenges and key aspects of ICNs.
The study provides the open issues for the researchers for
future research horizons. An other emerging field of net-
works is software define networks (SDN). The ref [7] pre-
sented the concept, architecture and challenges of SDNs and
virtualization. The study highlights the importance of SDN
and virtualization in wireless networks. The issues of mobile
adhoc networks (MANTs) are focused by the authors in [8].
For the controling of delay constrained in MANETs com-
munications, an cross layer distribution based algorithm
called interference-based topology control distribution
algorithm (ITCD) is proposed to overcome the issue of delay
in MANETs. The research and importance of multimedia
services in heterogeneous networks is carried out in [9]. The
role of context-aware middleware in multimedia services
and its frame work to understand its operations is discused in
detail. The research work in [10] discussed the issue of
routing protocol for heterogeneous Wireless Sensor Net-
work. The study implemented the energy-efficient delay-
aware lifetime-balancing data collection algorithms to
achieve reduced traffic cost in data collection and solve open
vehicles routing problems.
In recent years VANETs have gained a lot of popularity
among industry and academic research community.
VANETs use cars as a mobile nodes connected as ad-hoc
network manner. Every participating car behaves like a
wireless router or node to communicate with each other.
The fixed road side units like traffic light towers establish a
backbone network to provide connectivity, and in time
delivery of reliable safety, related information. The
VANETs standards, and implementations support growing
numbers of wireless products that can now be used in
vehicles [11]. For the better communications of the vehi-
cles, different dynamic routing schemes such as ad-hoc
based routing, location-based routing, cluster-based rout-
ing, and geocast routing are suggested [12].
In VANETs it is expected that, vehicles should timely
exchange the road data with each other, to avoid accidents.
For the efficient distribution of the contents such as data,
audio, and video, network coding is used to enhance net-
work performance in a dynamic environment [13]. Network
coding also makes the network more flexible by reducing
data transmission time. In dynamic road changing condi-
tions, VANET’s applications such as live video broadcast of
road traffic, and the dissemination of an accurate update is a
key requirement, to guarantee that receiver will be able to
download each bit of broadcasted data. Other advantages of
network coding such as reliability, robustness, and adapt-
ability make it a most widely used technique to improve
efficiency of communications protocols [14]. The VANETs
applications can be categorized into safety related appli-
cations and Internet connectivity-based applications [15].
Safety related applications include electronic brake warn-
ing, in-coming traffic warning, and intersection violation
warning [16] while cooperative downloading, content dis-
tribution, multicasting, and broadcasting fall in the domain
of Internet connectivity applications. The survey based on
wireless networks presented by researchers, cover the dif-
ferent domains of VANETs such as VANET’s applications
[16–18], routing protocols [19–22], trust management in
VANETs [23,24], and VANETs security [25]. Our research
paperpaper presents a very first comprehensive survey on
network coding-based applications of VANETs. It provides
different applications of VANETs using network coding
and their benefits.
Contribution of this paper: Our contribution in this
paper is as follows:
•We provide a comprehensive overview of network
coding.
•An overview of VANETs is provided.
•Different Network coding implementations in the
applications of VANETs are discussed in detail.
•We provide a comprehensive survey of different
network coding-based techniques in VANETs and
how these techniques are beneficial in the applications
of VANETs.
The rest of the paper is organized as follows: Sect. 2pro-
vides overview of network coding, Sect. 3has a discus sion
on VANETs. Section 4provides different approaches to
implement network coding in VANETs. Section 5discuses
the issues and gives the future research directions for net-
work coding in VANETs (Acronyms with their definitions
are given in Table 1).
2 Overview of network coding (NC)
Network coding is defined as applying codes at nodes in a
network [26]. It is a method of transmitting messages
across the network, that allows for recovery of lost data.
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Messages are broken up into chunks and coded with
information about the other chunks. In the event if one
chunk is lost the data in the other chunk can be used to
reconstruct the lost data at receiving end. By using network
coding, transmitted data is encoded and decoded to
increase network throughput, reduce delay, and to make
network more robust. Some advantages of network coding
are given below [26].
1. Throughput: The most well-known advantage of
network coding is throughput. It is achieved by
communicating more information with fewer packets.
2. Reduces Packet Loss: In packet networks, particularly
in wireless networks, packet loss is very common
issue. Packet loss in networks arises due to buffer
overflow, link outage, and collision. To avoid packet
loss, network coding is applied at intermediate nodes.
Network coding is also used to provide robustness
against link failures.
3. Security: Network coding provides security by sending
scrambled data i.e., combination of packets so that
attacker and malicious nodes are not able to find out
original data.
Network coding can be applied at different layers of
transmission control protocol/internet protocol (TCP/IP)
model and has many applications which are discussed
below.
2.1 Network coding in TCP/IP layer model
1. Concept of network coding can be applied at physical
layer to turn broadcast capacity into capacity boosting
advantages in wireless ad-hoc networks. Physical layer
network coding (PNC) is a scheme to coordinate
transmission among nodes [27]. The basic idea of PNC
is to exploit the network coding operation that occurs
when electromagnetic (EM) waves are superimposed
on one another.
2. The data-link layer in communications networks
performs the function of data moving in and out across
a physical link in a network. At data link layer store
and forward technique is used for transmitting of
information. Network coding is an extension in it
which performs operation on received data before
transmitting it [28]. It changes data link layer func-
tionality from ’’store and forward’’ to ’’store, process,
and forward’’.
3. Network layer has a responsibility of routing and
forwarding. Network coding based routing protocols
can be categorized into four types [29] such as routing
protocol based on clusters, routing protocols based on
data, routing protocols based on geographical location,
and routing protocols bases on power awareness.
Network coding is also used to control congestion in
network layer [30].
4. Transport layer provides end-to-end communications
for applications. Transmission control protocol (TCP)
is most commonly used, and reliable protocol in the
Internet. In mobile adhoc networks (MANETs), TCP
encounter many challenges such as route breaks due to
mobility, and time varying random error, due to
unpredictable link quality. To resolve these problems
a network coded multipath scheme, called CodeMP
[31] is proposed to support TCP in MANETs. User
Table 1 Acronyms with their Definitions
Name Abbreviations
ALM Application layer multicast
AODV Ad hoc on-demand distance vector routing
AWGN Additive white Gaussian noise
CCH Control channel
CFO Carrier frequency offset
CRNs Cognitive radio networks
CSMA/CA Carrier sense multiple access with collision avoidance
DGPS Differentiated global positioning
DSRC Dedicated short range communication
EDCF Enhanced distribution coordination function
EM Electromagnetic
GPS Global positioning system
ITS Intelligent transportation system
LAN Local area network
LMS Live multimedia streaming
MAC Multiple access control
MANET Mobile ad hoc network
MCD Mobile content distribution
MDC Multiple description coding
NC Network coding
OBU On board unit
ODMRP On demand multicast routing protocol
OFDMA Orthogonal frequency division multiple access
PLNC Packet level network coding
PNC Physical layer network coding
RSU Road side unit
QoS Quality of service
SLNC Symbol level network coding
TWRC Two way relay channel
TWRN Two way relay node
VANETs Vehicular ad hoc networks
V2I Vehicle to infrastructure
V2V Vehicle to Vehicle
WAVE Wireless access in vehicular environment
WLAN Wireless local area networks
WSNs Wireless sensor networks
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datagram protocol (UDP) is also a transport layer
protocol which is used to send time-sensitive data,
where packet dropping is tolerable such as multimedia
streaming applications over Internet. Therefore, a
hierarchal network coding [32] is proposed to save
bandwidth and avoid tight synchronization between
senders.
5. Application layer provides services for application
programs. Application layer multicast (ALM) [33]
protocols suffer from delay, throughput, and security.
To address these issues network coding techniques has
been introduced. ALM is implemented at end hosts
instead of network routers. Unlike network layer
multicast, application layer multicast requires no
infrastructure support, and can easily be deployed in
the Internet [34].
2.2 Applications of network coding
Network coding is useful in wireless sensor networks
(WSNs), under-water sensor networks UWSN, wireless
relay networks, wireless local area network (WLANs),
mobile ad-hoc networks, MANETs, wireless mesh net-
works (WMNs), and CRNs to provide applications, such as
reliable broadcasting, efficient data dissemination, trans-
port’s efficiency, recovery of data, and many more.
Broadcasting is a mechanism for disseminating identical
information from a sender to multiple receivers. Reliable
broadcast requires that every receiver must receive the
correct information sent by the sender. Network coding
refers to the ability of a node in the network to encode the
incoming data before sending this encoded data to the next
node. This recoding at intermediate node results in band-
width improvement [35]. A network coding based, R-Code
is proposed for reliable broadcasting in WMNs [33]. Use of
random linear coding is also beneficial for reliable broad-
casting [36].
Network coding is important for data dissemination in
many networks such as in WSNs. Software updating,
running on sensors is often necessary. It requires reliable
dissemination of data objects so, a network coding based
approach for data dissemination is proposed for reliable
delivery of information [37]. Network coding is also
useful in data recovery. On-the-fly data recovery schemes
[38] are proposed to enhance robustness of network
against packet loss. Network coding has also many
applications which are useful in different networks such
as file sharing in peer-to-peer networks [39], multimedia
streaming in VANETs [40] and spectrum shaping in
CRNs [41]. The role of network coding in multicast
communications for improved quality of service by using
multicast protocol is presented in [42,43]. The studies
suggested a routing protocol for multicast routing by
using the concept of pipelined network coding. An energy
efficient with enhanced throughput and fairness based
multicast routing protocol named as Codepipe is imple-
mented in ns2. The outcomes form the simulation shows
its enhanced performance as compared to other available
routing protocol in the literature.
3 Overview of vehicular adhoc network
(VANETs)
VANETs are particular kind of short-range wireless
communications MANETs. The vehicles in VANETs act
as a node, connected to each other to form a network.
Each participating vehicle has transmission capabilities.
The topology formed by the connecting vehicles is very
dynamic. It is due to the different traffic scenarios in
different hours and high mobility of vehicles. VANETs
ensure road safety by providing communications between
vehicles and having timely information about the road
incidents. In intelligent transportation system (ITSs) each
vehicle accept responsibility of sender, receiver, and
router, to broadcast information to transportation agency
which uses this information to provide safe, and free flow
of traffic [11]. For communications between vehicles and
road side units, vehicles must be equipped with some
radio interface and proper hardware to provide informa-
tion about location such as global positioning system
(GPS) and differentiated global positioning (DGPS)
receiver. Different models of communications are avail-
able in VANETs. A vehicle can communicate directly
with another vehicle, called vehicle to vehicle (V2V)
communications or can communicate with infrastructure
called road side unit (RSU) which is called as vehicle to
infrastructure (V2I) communications. The concept of
VANET is integrated with emerging technologies and
further discussed by different researchers. The authors in
[44] presented the application of cloud computing in
vehicular network. The idea is given how cloud technol-
ogy can be helpful for the multimedia applications in
vehicular technology. The paper summarize the issues and
challenges for the implementation of cloud computing in
VANETs. The study [45]on P2P-based vehicular networks
gives the fairness based media services distribution
strategy. The study focused the parameter of user satis-
faction and media content specification in the proposed
scheme to achieve fairness in sharing among multiple
vehicles
Some of the key factors of VANETs such as topology,
mobility and channel models, routing, and applications of
VANETs are discussed below.
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3.1 Topology
In particular, there is no fixed architecture or topology that
VANETs must have to follow. Although VANETs are par-
ticular kind of MANETs, but they are different from each
other in a sense that in VANETs vehicles do not move in
random manner. They have to follow a fixed path, while in
MANETs nodes move in a completely random manner. In
VANET’s architecture each vehicle consists of an on board
unit (OBU) which has wireless transmitter and receiver.
Three different communications scenarios can be defined
on the basis of OBU. Among them first scenario is that all
vehicles communicate with each other through road side
units. This architecture may resemble the WLAN. Second
scenario is like all vehicles communicate with each other
without any need of road side unit this resembles to ad-hoc
architecture, and the third scenario is called as hybrid
architecture in which some vehicles communicate without
road side unit while others need road side units [12].
To understand architecture of VANETs, it is important
to classify VANETs scenarios into three categories on the
basis of traffic conditions, namely rural, urban, and high-
way [46,47]. Each scenario has its own specific challenges
to overcome such as the sparse network in highways, have
prime issue of low density of vehicles, while in urban
environment low penetration ratio can cause long network
delays.
3.2 Mobility modeling
For an efficient, and realistic implementation of VANETs
in a highly versatile environment, an accurate mobility
model is required. Mobility model for VANETs is highly
concerned with the characteristics of vehicular mobility,
like acceleration, deceleration, changing lanes, and human
driving patterns. Lot of research have been done on the
useability of mobility models in vehicular communications.
The authors in [48,49] applied the fluid dynamic model in
mobility modeling for the density estimation of vehicles in
VANETs. Another study [50] applied queueing theory for
mobility modeling in VANET.
Mobility model can be classified at macro and micro
levels. Presence of streets, buildings, traffic signs, and other
features like road topology, road structure are considered at
macro level [51,52]. Behavior of vehicles like accelera-
tion, deceleration, and distance between vehicles is known
as micro level mobility.
Vehicular mobility models are classified into four dif-
ferent classes, which are briefly discussed below [53].
1. Synthetic model: Consists of five more classes i.e.,
stochastic model, traffic stream model, car flowing
model. Queue model, and behavioral model [53,54]
2. Survey-based models: It is a general model which is
able to reproduce deterministic behavior observed in
urban life.
3. Trace-based models: Used to generate mobility pat-
terns from movement traces.
4. Traffic simulator based model: Developed for urban
traffic engineering [53].
CityMob: A mobility pattern generator for VANETs [55],
has proposed many models for handling traffic. A brief
description of some of the models are given as follows.
(a) Simple model: It models horizontal and vertical
mobility patterns without considering change in
direction [55].
(b) Manhattan model: According to CityMob, in this
model all streets are two way with one lane in each
direction. Direction of each node is considered
random. This model also simulates semaphores at
random positions with different delays [55].
(c) Downtown model: This model is similar to Manhat-
tan model and adds traffic density to Manhattan
model [55].
3.3 Channel modeling
Channel modeling is the basis of VANETs simulation.
Channels in VANETs are affected by multiple factors,
including buildings, road situation, vehicle type, and rela-
tive velocity of vehicles. The authors in [56] has covered
the area of channel and propagation models in VANETs.
The research work provides the key knowledge about the
implementation and impact of channel and propagation
models on the protocols and applications in vehicular
communications. There are some algorithms like unit disk
model, stochastic large scale fading model, and obstacle-
based channel model. These models are used for estimating
the additional attenuation of signal, caused by other vehi-
cles in the surroundings [57].
1. Unit disk model: Vehicles can communicate with each
other only if they are within a threshold distance. This
model is widely used due to its simplicity [58]. The
sharp cut-off at the threshold distance fails to capture
the random noise, and sometimes even it make nearby
nodes unreachable.
2. Stochastic large scale fading model: This model takes
the average of additional attenuation carried to obsta-
cles. A vehicle can communicate with another vehicle
if it’s received signal power is greater than a certain
threshold value [59].
3. Obstacle-based channel model: This model is used to
incorporate the effect of surrounding hurdles such as
vehicles, walls, and buildings on the received signal
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strength rather than averaging the additional attenua-
tion due to these hurdles. This algorithm is proposed to
calculate additional attenuation caused by other vehi-
cles [60].
3.4 Routing in VANETs
Routing is the selection of best route for network com-
munications, and routing protocols are used to choose the
most appropriate path for reaching the destination. Per-
formance of a network depends on how well the routing
take place, which depends on the routing protocols used in
a network [61,62]. The issues of routing in different
ongoing adopted wireless technologies are focused by
many researchers. The problems of multicast routing in
MANETs is discussed in [63]. The issue of flooding is
addressed through the controling of the available resources
and parameters by using genetic algorithm in multicast
routing. The authors in [64] suggested a routing scheme by
considering the spatial resusability in wireless communi-
cations to improve throughput in multihop wireless net-
works. The presented spatial reusability-aware single path
(SASR) routing scheme gives improved results in end-to-
end throughput. A biology-inspired algorithm is derived in
[65] for steiner tree problem in wireless networks. The
algorithm named as physarum optimization is able to solve
the problem and provides better network coverage. A new
routing approach for DTN is presented in [66]. The routing
scheme is based on concept of back pressure theory which
considers the behaviour of each packet in making routing
decisions. To achieve the optimize routing solution the
authors in [67] applied the algorithmic game theory. The
study gain the quality of routing (QoR) by applying Nash
equilibria in routing games.
Routing is a challenging issue in VANETs. Vehicles act
as nodes in VANETs, while high mobility, frequent
changes in topology, and limited life time of a network are
such characteristics of VANETs that demand more effi-
cient routing protocols, which leads to low throughput,
high routing overhead, and hidden terminal problem [68].
Other challenging factors are road layout, and different
environment such as city and highway [69,70]. The idea of
delay tolerant networks in vehicular communications is
presented in [71]. The research work gives the routing
schemes implemented in vehicular delay tolerant networks
for the implementation of green vehicular networks. The
suggested directional routing and scheduling
scheme (DRSS) is able to overcome the scheduling prob-
lem having efficient energy management in VANETs. For
the secure and privacy aware communications in cloud
based vehicular DTN the authors in [72]gives the idea of
threshold incentive scheme (TCBI)in the routing of packets
in vehicular communications. The TCBI based scheme is
able to control the vehicular compromize and collision
attacks. It provides high delivery ratio and low delay in
communications.
Types of protocols used for routing in VANETs are
unicast, multicast/geocast, broadcast.
1. Unicast routing: Unicast routing protocols in VANETs
are used to transmit data from a single source to a
single destination. These protocols can be further
classified as, topology-based, position-based, cluster-
based and hybrid protocols [73].
2. Multicast routing: These routing protocols are used to
transmit data from single source to the group of
interested nodes. An extensive detail about the multi-
cast routing protocols can be seen in [74–76].
3. Broadcast routing: In VANETs broadcast routing
protocols are used frequently. Broadcast is used to
transmit data from single source to all nodes in the
network even unknown or unspecified nodes in the
network. More details about some broadcast routing
protocols in VANETs can be found at [77–79].
3.5 Applications of VANETs
The basic purpose of VANETs is to provide safe journey
on the roads and highways. In vehicular communications
mobility models plays an important role. The moving
pattern of vehicles impact the connectivity and applications
of VANETs. A vehicular network model normally consists
of three layers named as data traffic, vehicular traffic, and
road network [96]. Among them first two layers are con-
sidered dynamic, while third layer is considered as
stable and fixed. Applications of VANETs exhibit different
communications patterns like vehicle-to-vehicle commu-
nications, vehicle-to-road-side-unit communications, vehi-
cle communications with both vehicle and road side units.
Each pattern has different requirements such as bandwidth,
delay, security, and reliability.
VANETs applications can be divided into two broad
categories which are safety related applications and non-
safety related applications. Non-safety related applications
can be further divided into commercial applications, con-
venience applications and productive applications [97].
Safety related applications can be classified as real time
traffic applications (like information about traffic jams, con-
gestion, and alerts such as accidents and emergencies), co-
operative message transfer (this application automate things
like emergency braking and electronic brake-light is another
application used to avoid accidents), and post-crash notifica-
tions (this application provides road hazard control notifica-
tions, cooperative collision warning and traffic vigilance).
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Commercial applications include remote vehicle diag-
nostics, Internet access, digital map downloading, real time
video relay, and value added advertisement.
Convenience applications include route diversions,
electronic toll collection, parking availability, and active
prediction (it anticipates topography of road which is used
to optimize fuel usage).
Productive applications can be viewed as ’’time uti-
lization’’ which means if traffic is jam and user is waiting at
signal he/she can access the Internet for different services,
and can made his/her time more productive. The concept of
IoT, Cloud Computing, Smart Grid are merged with
VANETs for the betterment of mankind.
4 Applications of VANETs using different
network coding approaches
Network coding is used to provide various applications in
VANETs (see Table 2). It is used to improve efficiency,
and reliability of applications provided by VANETs.
Table 3provides a glance of benefits provided by VANETs
using network coding. It gives the overview about the
network coding implementations in different vehicular
applications. Some of the applications of VANETs which
use network coding,as mentioned in Fig. 1are described
below.
4.1 Physical layer network coding
The role of physical layer in vehicular communications
define the standards, technologies and physical protocols in
VANETs. The concept of physical layer network coding
(PNC) was first proposed in [98]. It is a way to exploit
network coding operations such as interference, that occurs
in superimposed electromagnetic waves [99]. One of the
biggest challenge in wireless communications was to deal
with such interference. When a particular receiver receives
radio wave signals, from more than one transmitter inter-
ference occurs. In radio channel, data is transmitted
through electromagnetic waves in a broadcast manner. The
interference among these electromagnetic waves causes the
data to be scrambled [27]. An application of network
coding directly within the radio channel at the physical
layer is proposed that is named as PNC [27]. The concept
of PNC can be illustrated with the example of two way
relay node (TWRN) explained in [99]. Two way relay
channel (TWRC) is an another PNC based three-node
linear network coding in which two end nodes, want to
communicate via a relay node R. There is no direct signal
path between node 1 and 2. An example is a satellite net-
work in which node 1 and 2 are the ground stations, and the
relay R is the satellite. PNC is used in wireless transmission
to avoid interference. It is also used in VANETs for the
efficiency, and reliability of periodic beacon messages
[95]. Broadcasting is an important application of PNC that
is discussed below.
4.1.1 Broadcasting in VANETs using PNC
VANETs play an important role in road safety by including
vehicle cooperation, and exchange of time sensitive
information such as location, speed, and acceleration, thus
provides awareness to vehicle about its surroundings.
Institute of Electrical and Electronic Engineers (IEEE) has
recently adopted a dedicated short range communications
(DSRC) radio technology under a new standard for
vehicular networks known as Wireless access in vehicular
Table 2 Network coding schemes in VANETs
VANETs applications NC scheme used References
Content distribution CodeOn technique [80]
Data mulling technique [81]
Relay and random NC [82]
Weak secrecy scheme [83]
Rank based NC [84]
CodeTorrent [85]
Routing Loss tolerant scheme in unicast routing, and NCMR [86,87]
MAC Network coded cooperative ARQ scheme, [88]
Opportunistic network coded Mac [89]
Multimedia audio video
streaming
Fuzzy redundancy adaptation and joint source network coding, CodePlay, and Multistream coding
with multi path and NC
[90–92]
Multi-hop wireless Joint fuzzy relays with NC, and integrated interflow and intraflow NC [93,94]
Broadcasting PNC [95]
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environment (WAVE) 8O2.11p protocol. DSRC band is
divided into seven 10 MHz channels, out of which one
channel, the control channel (CCH) is reserved for system
control, and safety related messages. Up to six channels,
are used to transmit non safety data. DSRC utilizes
orthogonal frequency division multiple access (OFDMA).
To ensure quality of service (QoS) carrier sense multiple
access with collision avoidance (CSMA/CA) or simply
CSMA together with enhanced distribution coordination
function (EDCF) is used. The technique CSMA/CA is
applied in such a manner that in communications a sender
node first sense the medium then forward the message. Due
to poor link qualities, transmission degradation, and high
collision, DSRC fails to ensure reliable, and efficient
broadcasting, which is required for safety related applica-
tions. Therefore, a PNC based, medium access control
(MAC) protocol for VANETs (VPNC-MAC) is
recommended in [95]. It uses PNC to ensure the efficiency,
and reliability of periodic beacons transmission in
VANETs. The implementation of PNC in VANET scenario
is performed by the researchers in a systematic way by
dividing the operation in two steps. The VPNC-MAC
protocol consists of two phases, setup phase and heart beat
packet exchange phase. In set up phase, VPNC-MAC uses
a location based OFDMA signaling technique to ensure a
quick and non-bandwidth consuming process. In packet
exchange phase, VPNC-MAC contains two periods of
variable and adjustable length. First period is guaranteed
time slot period called the VPNC-MAC session in which
node exchange their packets using PNC. The second period
is contention period reserved for the nodes unable to
transmit during VPNC-MAC session [95]. In [95], upper
bound of the transmission, that can be supported by both
optimal CSMA and VPNC-MAC is compared in which it is
assumed that only relay nodes can transmit during con-
tention period (CP). It is concluded that for low frequencies
the capacity supported by VPNC-MAC is slightly better
than CSMA since the number of transmissions are high.
The reason behind this is for low frequencies the time
difference between two PNC stages is less than optimal
CSMA. By using VPNC-MAC better reliability can be
achieved as compared to optimal CSMA, however the
primary issue with VPNC-MAC is time and frequency
synchronization, that is problem in highly dynamic tech-
niques such as OFDM. The suggested network coding
Table 3 NC schemes in VANETs and their benefits
NC schemes in VANETs Benefits References
PNC Fast data delivery [95]
Data mulling scheme Provides safety [81]
CodeOn Content broadcasting [80]
CodeTorrent Provides fast downloading [85]
Rank based NC Improves throughput [84]
Relay and random NC Provides high data delivery [82]
Weak secrecy scheme Provides secrecy of information [83]
NCMR Reduces interference [87]
NCCARQ-MAC Provides bidirectional communication [88]
VANETCODE Fast delivery of encoded blocks [111]
Opportunistic network coded MAC Better average delay performance [89]
Random linear NC Increases security [102]
NC based loss tolerant scheme Improves end to end packet delivery ratio [86]
NC schme in VANETs for cooperative scheduling Maximize throughput and minimize interference [101]
Multi-hop broadcasting using joint fuzzy relays Improves Recovery of lost packets [93]
Multi-hop broadcasting using interflow and intraflow NC Reduces number of transmissions [94]
Fuzzy redundancy adaptation Increases robustness of video streaming [90]
CodePlay Facilitate the dissemination of LMS [91]
Multi-stream coding with multi-path and NC Prioritize the data [92]
Applications of VANETs using NC
Physical Layer NC Content
distribution Routing MAC
Multimedia Audio/
Video Streaming
Multi-Hop
Wireless
Collaborative
Downloading
Scheduling Security
Fig. 1 Applications of VANETs using network coding approaches
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scheme at physical level helps to overcome the issue of
broadcsting in VANETs.
4.1.2 Feasibility of physical layer network coding
in VANETs
VANETs is considered to play important role in improving
road safety and traffic efficiency in daily life but the main
problem in VANETs is intermittent node connectivity and
relatively short contact duration due to high mobility of
nodes. Physical layer network coding (PNC) enables a data
exchange within a much shorter airtime which favors the
highly dynamic link connectivity in vehicular environment,
and appears as an important tool in VANETs. One of the
most important challenge in applying PNC to VANETs
comes from DOPPLER shift due to high speed vehicle
motion which leads to carrier frequency offset (CFO)
hence introduces inter frequency interference (ICI) that
degrade bit error rate performance [100].
In this feasibility study of PNC in 802.11p [100] authors
investigate the impact of motion induced CFO/ICI on the
overall signal detection. They investigate whether PNC in
VANETs can be made feasible with conventional equal-
ization techniques that suppress the effect of CFO. It is
concluded that PNC suffers only from 3 dB signal to
interference and noise ratio (SINR) penalty in worst case
compared with generic point to point communications.
Generally PNC is feasible in vehicular environment even if
the transmission power of nodes can not be finally con-
trolled [100]. The study shows that PNC supports in
VANETs higly dynamic link conditions when implemented
with conventional equalization technique.
4.2 Scheduling for cooperative VANETs
with networking coding
With the emergence of intelligent transportation system
(ITS), VANETs are receiving considerable attention. Such
systems will need to support both vehicle-to-infrastructure
(V2I) and vehicle-to-vehicle (V2V) communications. In
[101], information propagation problem in joint V2I and
V2V communications system is investigated. A scenario is
considered, where more base stations (BS) are allocated
along the road, so that the information centers are able to
broadcast timely messages to the vehicles, within the range
of broadcast signal of each BS, which is referred to as
broadcast zone. The seamless information spread is used to
guarantee that the messages are correctly received by each
vehicle regardless of whether, it pulls into broadcast zone
or not. The study helps in the implementation of ITS idea
in real worlds. As the vehicles cooperating in communi-
cations require timely distribution of important data. In
[101], maximum throughput is derived for V2I down link
system for additive white Gaussian noise (AWGN) chan-
nels and rayleigh fading channels with Doppler Effect.
Maximum achievable amount of information that can be
forwarded along a vehicular stream using vehicle relaying
is also calculated, and cancelation of interference is also
achieved, by the use of network coding along with inno-
vative design of transmission of scheduling. Under the
implementation of network coding the scheduling for
transmission is improved.
4.3 Security threats and solutions and network
coding based security approaches for VANETs
VANETs have numerous applications which include traffic
awareness, accident detection, automatic toll paying, col-
lision avoidance, and internet usage on roads. As VANETs
use wireless communications, one important issue is to
handle privacy, security, and reliability. Various threats
such as malicious nodes, wormhole attack, accidents, and
password breach should be paid special attention to avoid
difficulties especially where life crucial information is
involved. Due to the data tempering in VANETs different
security algorithms are suggested in the literature. Some
major threats to VANETs are message forging, imperson-
ation, packet dropping, black hole, Sybil attack, hidden
vehicle problem, and on board tempering. Some schemes
for various threats such as packet leashes, short message
services to VANETs, Sybil attack witness, and trust-based
neighbor table scheme are mentioned in [102]. In [102],
authors present that all of these schemes failed to provide
security and reliability simultaneously, so a linear network
coding is proposed to encode packets as linear combination
of original packets. A meaningful coefficient is needed for
encoding and decoding therefore, linear network coding
requires central authority to control generation of mean-
ingful coefficient. Algorithms employed for linear network
coding should be centralized but the vehicular environment
is highly dynamic so, a heterogeneous and distributed
approach is needed. A Random linear network coding is
suggested for random generation of the coefficient. In this
approach though the computational overhead may increase
but security and reliability is ensured. The linear network
coding scheme is able to enhance the data security level in
VANET environments.
4.4 Content distribution
Content distribution refers to a file sharing or multimedia
sharing. With network coding, each node of the distribution
network is able to generate and transmit encoded blocks of
information. The randomization introduced by the coding
process eases the scheduling of block propagation, and
thus, makes the distribution of network more efficient
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[103]. The operations of VANETs relay on the timely
distribution of data. The different applications across
VANETs provide useful information for the drivers and
passengers. The improvement in data delivery across the
network is key focused area in different studies. Network
coding is beneficial for content distribution in peer to peer
networks, wireless networks, and VANETs. In VANETs
content distribution ensures safety related application to
avoid accidents, by providing location update. It also pro-
vides non-safety related applications such as Internet based
entertainment.
4.4.1 Techniques of content distribution
Different techniques are used to distribute the contents
such as a file, that are mentioned in Fig. 2.
1. Data mulling technique
The basic purpose of VANETs is to enhance safety by
providing an early warning system for the drivers so that
their timely decisions can safe human lives. Warning sys-
tem should be able to deliver the safety messages in a
timely manner. Data mulling technique [81], along with
network coding, erasure coding, and repetition coding is
proposed for reliable and timely data dissemination. In data
mulling technique the problem of delayed delivering of
large data to disconnected platoons on highway is explored.
The traffic conditions on the road is utilized in this study.
Vehicles moving in opposite direction act as data mules. It
is proposed that network coding performs best as compare
to erasure coding, and repetition coding. The platoon for-
mation characteristic of vehicular communications is sup-
porting the concept of data mulling technique. This reduces
the data delay in highways.
2. CodeOn technique
One of the key service offered by vehicular network is
popular content distribution (PCD). The concept of
VANETs is explored by the industry to facilitate passen-
gers by providing relavent and interesting information
during their journies. A novel push based PCD
scheme called CodeON is introduced in [80]. In this
scheme contents are actively broadcasted to vehicles from
road side access points (AP), and then further distributed
among vehicles using cooperative VANET Symbol level
network coding. This is used to combat the lossy wireless
channel. Performance of CodeOn is evaluated from three
aspects named as downloading progress, average down-
loading delay, and average downloading rate. These
parameters helps to evaluate the network performance in
data distribution.
3. CodeTorrent technique
In this technique, authors investigate the problem of
running BitTorrent type P2P file sharing systems, i.e., file
swarming protocols in VANETs. Mobile peer to peer
systems have gained a large attention in research domain.
Researchers are trying to build an efficient and effective
mobile content addressable network. This will improve the
data transfer rate in vehicular communications.
A network coding based file swarming protocol is pro-
posed in [85], which supports VANETs and allows shorter
file downloading time as compared to existing VANET file
swarming protocol which shows less performance in peer
to peer implementation.
4. Rank based network coding
Rank based network coding scheme is proposed in [84],
for distributing content in VANETs. This is used to adap-
tively broadcast packets based on content reception status
of neighbors. Simulation results demonstrate that the pro-
posed method improves the throughput by more than 32 %,
while maintaining lower end-to-end delay, as compared to
CodeOn technique [84]. By reducing the end to end delay
the nodes are able to receive data timely.
5. Relay and random network coding
Distributing data items such as pictures, and videos
about traffic condition for a driver to go to a specific
location is great challenge for VANETs due to network
dynamics and high mobility. In ITS the availability of
multimedia services require fast data delivery
A scheme is proposed in [82] called RNC-based regio-
nal data distribution on VANETS (R2D2V). This is a rapid
and reliable data dissemination using random network
coding. R2D2V can achieve a high data delivery ratio for
vehicles being driven in the surrounding areas of a location
where the information was generated during the informa-
tion effective period using VANETs. It provides low data
delivery traffic, and short delays when the vehicle density
is high. However the scheme is not able to achieve high
delivery ratio for vehicles that arrives after the generation
of information. The impact of late coming vehicles on the
data distribution at the place of data generation is over-
looked by the technique
Content distribution in VANETs using network coding
Data mulling
Technique
CodeOn
Technique
Code Torrent
Technique
Weak secrecy
scheme
Relay and Random
Network Coding
Rank Based
Network Coding
Fig. 2 Network coding schemes in VANETs for content distribution
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6. Weak secrecy scheme
An efficient mechanism is proposed in [83] to maintain
the secrecy of information. This scheme is based on
obfuscation by processing and coding the original file so
that only the intended recipients informed of corrupted
blocks can recover the information timely. File distribution
in VANETs use weak secrecy scheme, which enhances
content distribution in terms of downloading.
4.4.2 Minimizing data delay in content distribution
In VANETs, for large number of applications the alert mes-
sage is the whole information needed by vehicles present in
that given area. So broadcast is an essential feature for com-
munications. Due to packet loss in wireless communications
delay based broadcast protocols are combined with network
coding through a new protocol called delay based oppor-
tunistic network coding protocol [104]. It is used for canceling
the effect of packet loss and implicit acknowledgement issues.
4.4.3 Processing overhead of network coding in data
dissemination
Content distribution in vehicular networks such as multimedia
file sharing and software update is a big issue due to dynamic
network and high speed mobility. Network coding has been
proposed to enhance the performance in high dynamic envi-
ronment. The techniques applied by different researchers
focused to improve the data delivery ratio, data delay and
packet lost ratio. An in-depth analysis is conducted in [83]to
address the implementation issues of network coding.
The main focus of this analysis is to investigate impact
of practical resource constraints such as disk access,
computational overheads, and memory constraint on per-
formance of content distribution using network coding in
highly dynamic environment such as VANETs [105].
The key points of analysis are
•Resource constraints have significant impact on per-
formance of network coding.
•Data pulling can significantly improve performance.
The data delivery ratio is improved across the network
•Benefit of sparse random network coding is not always
obvious and its parameters should be carefully chosen
to perform well.
•Generation level chucked code is not efficient in highly
dynamic environment. [105].
4.4.4 Throughput analysis
Due to the dynamic road conditions and divers vehicular
behaviour VANETs have fast changing topology and lossy
wireless channel. Various protocols have been proposed in
[83] to enhance performance of mobile content distribution
(MCD) in vehicular environment using packet level net-
work coding (PLNC) and symbol level network coding
(SLNC). A theoretical model is proposed in [83] to com-
pute achievable throughput of cooperative MCD in
VANETs using SLNC. In this model one dimensional road
topology is considered with access point as content source
and expected achievable throughput for a vehicle at a
certain distance is derived by using both PLNC and SLNC.
The difference in achievable throughput between SLNC
and PLNC is determined by symbol level diversity.
Throughput in VANETs is also studied in [106] under
two different distribution models. The study have per-
formed throughput analysis for both models under diverd
road conditions. One of selected modelsis uniform distri-
bution and other is regular network with equal inter-dis-
tance. it showed that under fast fading channel, SLNC has
much higher gain over PLNC while expected achievable
throughput of PLNC is nearly zero.
4.5 Routing in VANETs
Routing in VANETs is a challenging issue due to highly
dynamic nature of vehicular networks. When thinking
about the routing under VANETs the key aspects to con-
sidered is the changing road conditions and heteroge-
neousness in vehicles types. It is difficult to provide
reliable and continuous communications in fast moving
vehicles. Different routing protocols such as unicast, mul-
ticast and Geocast [107] are used to disseminate informa-
tion among the vehicles on the road. These routing
protocols are dependent on various internal and external
factors. Internal factors such as mobility, while external
factors include road topology and hurdles on the road that
block the signals [108]. Figure 3shows some routing
protocols which are implemented through network coding.
4.5.1 Loss tolerant unicast routing
The main goal of unicast routing in VANETs is to transmit
data from single source to single destination. In V-2-V
communications it is required to have efficient data
delivery In VANETs designing an efficient routing proto-
col is challenging task due to lossy wireless channel.
A packet can be lost at an intermediate node, even when
a proper node is selected. Therefore, a loss tolerant
scheme is proposed in [86] for unicast routing. This
scheme uses multiple intermediate nodes to improve the
packet reception ratio and uses network coding to reduce
the number of required transmissions which results in a
significant improvement in end-to-end packet delivery
ratio, without increasing message overheads.
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4.5.2 Network coding-based multicast routing
Multicast routing can efficiently improve the utilization
and scalability of wireless links. The data communication
environment in VANETs is effected by the dynamic road
conditions. Integration of multicast routing and network
coding helps in enhancing the network performance.
Therefore, a network coding based multicast routing
algorithm (NCMR) is proposed in [87]. It is based on local
topology information. It is combined with location infor-
mation provided by global positioning system (GPS) sys-
tem in vehicles. NCMR reduces communications
interference, provides higher reception rate, balance the
network load and guarantees quality of service (QoS).
Multicast routing can also be implemented with ad hoc
on-demand distance vector (AODV) scheme which uses
group identification, local area network (LAN) identifica-
tion, and node identification to recognize the node and
related areas. It works like dynamic host configuration
protocol (DHCP). When a car enters in a network RSU
allocates a unique group id to that car which is not per-
manent when this car will pass through another RSU
another group id will be allocated to it [109]
4.6 MAC in VANETs with network coding
The media access control (MAC) is a data communications
network protocol sub-layer, also known as the medium
access control. It is a sub-layer of the data link layer
specified in the seven-layer OSI model. The medium access
layer was made necessary by systems that share a common
communications medium. The data frames at data link
layer under different technologies shows different beha-
viour. MAC is implemented through network coding
techniques to enhance the total bandwidth of the network,
and to minimize the average delay. Figure 4shows the
network coding based MAC protocols in VANETs
4.6.1 Network coded cooperative ARQ scheme
In [88], authors present a network coding based, medium
access control protocol for VANETs. It uses cooperative
automatic repeat request (ARQ) technique. This network
coding based cooperative automatic repeat request protocol
(NCCARQ-MAC) coordinates the transmission among a set
of relay nodes which act as helpers in bidirectional com-
munications that occur in VANETs. The study implemented
the suggested MAC layer protocol in a urban dense envi-
ronment to achieve bidirectional communications.
The main contribution of this scheme is the fusion of
cooperative ARQ and network coding technique to
enhance system performance. As compared to simple ARQ
protocol, this scheme enhances network aggregated band-
width up to 80 %. It minimizing total number of trans-
missions, and average time to transmit data packets.
4.6.2 Opportunistic network coding-based MAC
It is the application of ITS that provide cooperative driver
assistance in VANETs. Every vehicle periodically gener-
ates a small size message that is less than 200 bytes, which
contain the necessary information about the vehicle. Goal
of this communications is to provide a reliable and up to
date knowledge about neighborhood for each vehicle pre-
sent on the road. Each message has a typical life time of
200 ms after which it is of no use. This local information
can avoid accidents and assists the driver to choose alter-
native strategies such as taking over or turning [89].
An opportunistic network coding algorithm for safety
message dissemination is proposed in VANETs [89]. In
high traffic load the opportunistic network coding provides
best performance in terms of loss probability, and also has
a better average delay performance as compared to random
linear coding.
4.7 Collaborative downloading
Collaborative downloading is a data dissemination protocol
which is used to distribute information among all the nodes
in a network. Data dissemination in VANETs consist of
two implementations.
Road side base stations (BS) to vehicles: Vehicles
communicate with BS to receive and sharing of the data.
Vehicle-to-vehicle communications: When vehicles are
out of coverage of BS, they try to exchange the information
with each other. In this phase all vehicles have same
information.
Routing in VANETs
Loss tolerant
scheme for
unicast
routing
Network
coding-based
multicast
routing
Fig. 3 Routing in VANETs using network coding
MAC
Network Coded
Cooperative ARQ scheme
Opportunistic Network
Coded Mac
Fig. 4 Network coding based MAC in VANETs
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By using network coding in collaborative downloading
which is proposed in [110] we can eliminate need for
signals because, for transmitting the data from infrastruc-
ture to the vehicles there is no need for the BS to know
which data packets the vehicles already possess. This also
makes latency of the network better.
4.7.1 VANETCODE for collaborative downloading
VANETCODE is based on the concept of network coding.
In this scheme presented in [111], content is divided into
smaller blocks and nodes linearly encode these constituent
block. The resultant blocks are then shared among neigh-
boring nodes. In Ad Hoc networks since each node acts as a
router so network coding can be done at network layer for
each node. This scheme also takes the advantage of
broadcast nature of wireless medium to speedily distribute
the encoded blocks among one-hop neighbors. VANET-
CODE eliminates the need of peer selection, content
selection, and neighbor discovery which take up significant
amount of time and resources, in other cooperative
downloading mechanisms proposed for VANETs [111].
4.8 Multi-hop wireless networks under network
coding
In multi-hop wireless networks, communications between
two end nodes is carried out through a number of inter-
mediate nodes whose function is to relay information from
source to destination [94].
In VANETs, timely dissemination of safety messages is
a key concern. For the safe and secure traveling on the road
the in time delivery of important information about the
road conditions is required. Therefore, due to limited range
of wireless devices many safety applications require multi-
hop broadcast protocols to distribute safety related mes-
sages [93,94]. Some of the network coding-based multi-
hop wireless communications techniques are mentioned in
Fig. 5.
4.8.1 Multi-hop broadcasting using joint fuzzy relays
This scheme uses a fuzzy logic algorithm to choose the
next hop relay nodes and uses network coding to improve
the packet dissemination ratio without increasing message
overhead. By using fuzzy logic algorithm the protocol can
choose the best relay node by taking into consideration the
inter vehicle distance, vehicle velocity, and link quality.
The relay nodes cooperate with each other to recover lost
packets by employing a network coding algorithm to
encode packets [93]. The study has presented the concept
of integrating of Fuzzy logic with network coding to
overcome the issues of broadcasting in VANETs
4.8.2 Multi-hop broadcasting by integrating interflow
and intraflow network coding
For broadcasting messages in VANETs, a Multi-hop
broadcasting protocol, is proposed in [94] which employs
interflow and intraflow coding to reduce the protocol
overheads as compared to traditional protocols. This pro-
tocol can improve packet reception probability at receiver
node by using network coding. Therefore, this protocol is
able to provide light weight and reliable solution for data
dissemination in VANETs [94].
Advantages of this protocol includes:
•Interflow network coding can significantly reduce
number of re-transmissions.
•Intraflow network coding can improve packet dissem-
ination ratio.
This results in shorter MAC layer contention time at each
node and lower end to end delay [94]. The research work
reduce the network congestion and improve the data
delivery in VANET communications under multihop
manner.
4.9 Multimedia audio/video streaming with network
coding
Streaming exists more commonly in the form of audio and
video. When a multimedia file can be played or can be
presented to the end user without downloading is known as
multimedia streaming. In VANETs multimedia streaming
is an important application. The concept of multimedia
services in VANETs providing new domains of research.
VANETS use network coding to provide faster transmis-
sions,and better video quality. Some multimedia streaming
applications of VANETs, which make use of network
coding are discussed below and mentioned in Fig. 6.
4.9.1 Fuzzy redundancy adaptation and joint source
network coding based video streaming
VANETs support many video applications. Delivering
video to moving vehicles is very challenging due to dif-
ferent aspects of mobility. In [90] authors propose a
Muti-Hop Wireless
Multi-Hop Broadcasting
using interflow and
intraflow network coding
Multi-Hop broadcasting
using Joint Fuzzy Relays
Fig. 5 Multi-hop wireless communications in VANETs using
network coding
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reliable approach for video streaming based on random
practical network coding and source coding. In this
approach, it is proposed to implement, NC above the MAC
layer. Multiple description coding (MDC) operations are
embedded in application layer. Robustness of video
streaming increased in vehicular networks by two stages of
coding. Redundancy of network coding is also adjusted by
using fuzzy inference system controller. To minimize the
end-to- end delay, mathematical analysis is also derived for
latency. Authors also showed results with NS-2 simulator
which shows that video quality, packet loss ratio, and
application layer throughput is improved.
4.9.2 Emergency related video streaming under network
coding
The researchers in [40], focusedthe problem of dissemi-
nating emergency video streams after an accident, to the
coming vehicle is considered. Video dissemination to
vehicles connected to the source can benefit from network
coding especially in fast mobility and when radio channel
is degraded by errors and interference. Network coding
ensures 100 % delivery ratio while a most robust on-de-
mand multicast routing protocol (ODMRP) yields only
92 % delivery ratio. The impact of network coding
improves the packets delivery ratio under dynamic road
conditions
The problem of delayed delivery of video is also
explored. If columns of vehicles on the road has gaps,
network coding jointly with data mulling on vehicles in the
opposite direction can deliver the multimedia files to the
disconnected components faster than other known schemes
[40].
4.9.3 CodePlay: symbol level network coding based
multimedia streaming
The fundamental challenge of providing live multimedia
streaming (LMS) services in VANETs, come from
achieving stable and high streaming rate for all the inter-
ested vehicles. By using minimal bandwidth resources
especially under highly dynamic topology of VANETs and
lossy nature of vehicular wireless communications. Symbol
level network coding can improve efficiency of bandwidth
utilization by exploiting both wireless symbol level diver-
sity and benefits of network coding. This network coding
scheme provides stable vehicular communications which
supports running of multimedia services at application
layer.
The core of CodePlay [91] is a coordinated local push
mechanism with symbol level network coding that estab-
lishes a local and distributed coordination among vehicles
to ensure stable and high streaming rates. Even using
SLNC, there is still need of few additional APs along the
road and well-designed channel usage mechanisms to
facilitate the dissemination of LMS content to end users.
4.9.4 Multi-stream coding with multi-path and network
coding
Due to the changing road conditions packet loss and delay
are very common in VANETs. Real time traffic can tol-
erate some packet loss, for text data reliable transmission
protocol is required. In[92], author propose a robust
scheme for salable video coding- based streaming over an
urban VANETs with path diversity and network coding. In
this scheme, the time critical data is transmitted, based on
priority and path quality. The high priority data is trans-
mitted through high quality path, and the lowest priority
data through lowest quality path. The quality of the path is
calculated on the basis of grey relational analysis.
5 Issues and future research directions of network
coding in VANETs
There are penalty of issues with VANETs. Main problem
with VANETs is their dynamic and versatile nature. Some
of the key issues and future research directions are given
below.
5.1 PNC feasibility
PNC enables data exchange within a much shorter airtime,
which favors the highly dynamic link condition in vehic-
ular environment and hence appears to be a powerful tool
in VANETs. In [100], an important issue on feasibility of
PNC is discussed. Limitations of doppler shift are addres-
sed specifically. It is also mentioned in [100], more
advanced equalization techniques for PNC, can be studied,
by considering high order modulation schemes.
5.2 Data distribution
Distributing data items about traffic conditions poses a
great challenge due to network dynamics and high-speed
Multimedia Audio/ Video Streaming
Fuzzy
Redundancy
Adaptation
Emergency
Related
Video
Streaming
CodePlay
Multi-
Stream
Coding
Fig. 6 Multimedia audio/video streaming in VANETs using network
coding approaches
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mobility. To provide continuous information about vehi-
clesR2D2V scheme is proposed in [82] which uses random
network coding to deal with packet collisions. This
scheme provides high data delivery rate. In future scala-
bility of this scheme should be examined. Moreover, there
is a need to further investigate data dissemination strategies
for VANETs as well [112–114].
5.3 Processing overheads of NC
Content distribution in VANETs, such as multimedia file
sharing is a great challenge due to network dynamics and
high mobility. In recent years, network coding has been
shown to efficiently support distribution of content in such
dynamic environments, thereby considerably enhancing the
performance. However, the related work in the literature
has mostly focused on theoretic or algorithmic aspects of
network coding so far. In [105], it is studied that resource
constraints have significant impact on performance of
network coding. Data pulling which considers the resource
constraints at remote node can improve performance. It is
also studied that generation level chucked coding is not
efficient in VANETs so this issue should be addressed
properly.
5.4 MAC
VPNC-MAC is proposed in [95] which uses PNC to ensure
reliability and efficiency of periodic beacon messages.
However the problem is that VPNC-MAC relies on time
and frequency synchronization which is a primary issue in
dynamic environment such as VANETs. As a future
research direction, significant elements can be provided to
ensure performances of VPNC-MAC while considering
time and frequency errors [95].
5.5 Sender oriented broadcast
In vehicular ad hoc networks (VANETs), a multi-hop
broadcast protocol is required to disseminate traffic warning
information. To reduce broadcast message overhead while
maintaining a high dissemination ratio is a very challenging
task. Network coding assisted cooperative relay scheme is
proposed in [115] for sender-oriented multi-hop broadcast
protocols in VANETs. This scheme significantly increases
packet dissemination ratio without increasing message
overhead. In future, inter-flow network coding can be con-
sidered to improve the overall throughput.
5.6 Congestion control
A rank based network coding scheme is proposed in [84]
for content propagation in VANETs in which vehicles
adaptively broadcast packets based on the content recep-
tion status of their neighbors. This scheme provides a better
method to reduce congestion and stto improves the
throughput more than 32 % while maintaining lower end-
to-end delay and protocol overhead. In future analytical
model can be improved by relaxing the assumption of
using equivalent carrier sensing and communications
range.
5.7 Security
VANETs are the promising approach to provide safety and
other applications. A lot of works have been done towards
it but security in VANET got less attention while security
is a big threat in VANETs, as it is self organized. There is
high possibility of security risks such as malicious nodes,
wormhole attack, and password breach,in connecting with
the network. In [102], author presented many security
threats which can be lethal in so many prospective,this
problem should be addressed properly.
5.8 Routing protocols
Researchers have proposed many routing protocols for
safer and faster traffic flow in the network for high mobility
and dynamic topology, but due to complexity of VANETs
routing is still big issue.
5.9 Quality of service (QoS)
Quality of service is an important phenomena in any type
of network. Data delivery with minimum delay, less re-
transmissions of data, and controlling jitters are the main
consideration of QoS. Providing all these parameters in
VANETs is a big issue and an important research
challenge.
Besides the aforementioned issues, there is a need to use
cognitive radio technology in VANETs. Cognitive radio
technology has many applications [116–119]. CR tech-
nology can be used to alleviate the problem of spectrum
scarcity [120].
6 Conclusion
In this article, we have presented a comprehensive survey
of network coding in VANETs. Different network coding-
based applications in VANETs such as physical layer
network coding, broadcasting in VANETs, content dis-
semination in VANETs, routing in VANETs, collaborative
downloading, medium access control related applications,
multi-hop wireless, and audio/video streaming during
vehicular communications are discussed in detail. We
Wireless Netw
123

presented various network coding schemes implementa-
tions in VANETs and their benefits. This paper concludes
that with the effective use of network coding in VANETs,
their performance, throughput,can be significantly
improved. It can enhance security in vehicular
communications.
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Farhan Jamil received the
Bachelor degree in Telecom-
munication and Networking
from COMSATS Institute of
Information Technology, Wah
Cantonment, Pakistan, in 2015.
He achieved Campus Silver
Medal in Bachelor degree. He is
currently M.S. scholar in Bei-
jing Institute of Technology
(BIT), Beijing, China. His
research interest includes ad-
hoc networks, mesh networks,
sensor networks, digital logic
synthesis and digital chip
designing.
Anam Javaid received the
Bachelor degree in Telecom-
munication and Networking
from COMSATS Institute of
Information Technology, Wah
Cantt, Pakistan in 2015. She
achieved Campus Gold Medal
in Bachelor Degree. Currently,
she is a M.S. scholar, and
Research Associate in COM-
SATS Institute of Information
Technology, Wah Cantt, Pak-
istan. Her research interest
include vehicular ad-hoc net-
works, and wireless sensor
networks.
Tariq Umer (M’16) received
his Ph.D. in Communication
systems in 2012 from School of
Computing and Communica-
tion, Lancaster University, UK
and Master in Computer Sci-
ence in 1997 from Bahauudin
Zakariya University, Multan,
Pakistan. During Ph.D. studies
he worked on mobility and
connectivity modeling for
vehicular ad-hoc network. He
has been serving in IT education
sector of Pakistan for the last
13 years. Currently he is work-
ing as Assistant Professor in CS department of COMSATS Institute of
Information Technology, Wah Cantt. His research interest includes
vehicular ad-hoc networks, telecomm network design and manage-
ment, wireless sensor networks and routing and switching. He has
been serving as guest editor for IEEE ACCESS and TPC member for
FIT 14, 15.
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Mubashir Husain Rehmani
(M’15, SM’16) received the
B.E. degree in computer sys-
tems engineering from Mehran
University of Engineering and
Technology, Jamshoro, Pak-
istan, the M.S. degree from the
University of Paris XI, Paris,
France, and the Ph.D. degree
from the University Pierre and
Marie Curie, Paris, France, in
2004, 2008, and 2011, respec-
tively. He is currently an
Assistant Professor with COM-
SATS Institute of Information
Technology, Wah Cantonment, Pakistan. He was a Postdoctoral
Fellow with the University of Paris Est, France, in 2012. His research
interests include cognitive radio ad hoc networks, smart grid, wireless
sensor networks, and mobile ad hoc networks. He served in the TPC
for the IEEE ICC 2015, the IEEE WoWMoM 2014, the IEEE ICC
2014, the ACM CoNEXT Student Workshop 2013, the IEEE ICC
2013, and the IEEE IWCMC 2013 conferences. He is currently an
Editor of the IEEE COMMUNICATIONS SURVEYS AND
TUTORIALS and an Associate Editor of the IEEE Communications
Magazine, IEEE ACCESS, Computers and Electrical Engineering
(Elsevier), Journal of Network and Computer Applications (Elsevier),
Ad Hoc Sensor Wireless Networks, Wireless Networks (Springer)
journal, and the Journal of Communications and Networks. He is also
serving as a Guest Editor of Ad Hoc Networks (Elsevier), Future
Generation Computer Systems (Elsevier), IEEE ACCESS, Pervasive
and Mobile Computing (Elsevier), and Computers and Electrical
Engineering (Elsevier). He is the founding member of IEEE Special
Interest Group (SIG) on Green and Sustainable Networking and
Computing with Cognition and Cooperation.
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