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1.1 Wireless Communication
Wireless communication is used to transfer information between two or more points that have no physical connection. The distance between communicating points can be short, such as a few meters for AC remote control, or even millions of kilometers for deep space radio communications. It encompasses various types of personal digital assistants (PDAs), portable two-way radios, cellular telephones and wireless networking. Some other examples of wireless technology are cordless telephones, garage door openers, wireless computer mice, keyboards and headset, radio receivers, satellite television etc. Wireless operations allow services such as long range communications. These types of communications are impossible or impractical to implement with the use of wires.
1.1.1 Common examples of wireless equipments include:
Telemetry and traffic control systems.
Remote control devices using infrared and ultrasonic waves technology.
Modulated laser light systems used for point-to-point communications.
SMR (Specialized Mobile Radio) and professional LMR (Land Mobile Radio) used by industrial, business and public safety systems.
Consumer two way radio including GMRS (General Mobile Radio Service), FRS Family Radio Service, and Citizens Band ("CB") radios etc.
The Amateur Radio Service (Ham radio).
Consumer & professional Marine VHF radio.
Radio navigation equipments that are used by aviators and air traffic control systems.
Cellular telephones and pagers.
Connectivity for portable and mobile applications.
Global Positioning System (GPS)  that allows drivers of cars, captains of ships, and pilots of aircraft to ascertain their location anywhere on earth.
Cordless computer peripheral devices. For example the cordless mouse, keyboards and printers can be linked to a computer via wireless using technology such as bluetooth.
Limited-range devices such as cordless telephones.
Satellite television which broadcasts from satellites in geostationary orbit. Typical services use direct broadcast satellite that is used to provide multiple television channels to viewers.
1.2 What are Ad hoc Networks?
The networks without any centralized or pre-established infrastructure are known as Ad hoc networks. Ad hoc networks are a collection of self-governing mobile nodes . Self-configuration and self- healing are the key characteristics of ad hoc networks.
1.2.1 Characteristics of ad hoc networks
The characteristics of these networks are as follows:
They communicate via wireless means.
Nodes act both as hosts and routers.
There is no centralized controller and infrastructure.
Network topology is dynamic and frequent routing updates occur.
They are autonomous and no infrastructure is required.
Can be set up anywhere in short time.
More energy constraints.
Security is limited.
Self-configuring nodes also serve as routers.
Self-healing through re-configuration process.
Scalable (accommodates addition of nodes).
1.2.3 Limitations of Ad Hoc Networks:
Some limitations of ad hoc networks are:
Every node of the network must have full performance
System loading effects throughput
Reliability requires a sufficient density of nodes. Sparse networks can have problems
Large networks can have latency.
1.3 What are MANETs?
A Mobile Ad hoc Network (MANET) is an autonomous collection of mobile nodes that can communicate over relatively bandwidth-constrained wireless links. Nodes in the network are mobile and network topology may change unpredictably over time. The network is decentralized. Nodes perform all network activities including discovering the topology. Messages delivery is also executed by the nodes themselves. This means that routing functionality is incorporated into mobile nodes.
1.4 What are VANETs?
Vehicular ad hoc Network (VANET) is a type of ad hoc network in which moving vehicles act as nodes of the network. Vehicles communicate wirelessly through multi-hop paths. Vehicles use intermediate vehicles as relays to carry data to final destinations. Higher node mobility, rapidly changing network topology are the main characteristics of VANETs. This means that network topology is highly dynamic .
Fig. 1.1 vehicle to vehicle communication in VANETs
Main objective of VANETs is safety and handling of emergency situations. VANETs assist drivers to communicate among themselves to avoid any critical situation e.g. road side accidents, traffic jams and speed control etc. In case of an accident or sudden hard breaking, a notification is sent to the preceding cars. Cooperative driver assistance system may be used for message propagation. It exploits the exchange of sensor data or some status information among cars. The drivers thus get information about obstacles and hazards. Besides safety applications VANET also provide comfort applications to the road users. For example, weather information, mobile e-commerce, Internet access and other multimedia applications . VANETs do not use any telecommunication infrastructure. However, infrastructure is used in intelligent transportation systems (ITS) [5, 6].
VANET is a special type of MANET where vehicles act as nodes. Unlike MANET, vehicles move on predefined roads/paths. There are many challenges in VANET which need to be solved to provide reliable services.
Reliable routing in VANET is one of the major issues. Vehicles have dynamic behavior in VANETs and high speed of vehicles make routing more challenging. Routing in MANETs (Mobile Ad hoc Networks) is not as difficult as in VANETs. This is due to less mobility of nodes. Many routing protocols such as AODV , DSR  have been developed for MANETs. These protocols fail to perform for VANETs due to high mobility of vehicles. Frequently changing network topology of VANETs hinders path determination as well as path maintenance process.
Scarcity of bandwidth in wireless communication is another issue. Available bandwidth may be wasted by the unnecessary rebroadcast of data and control packets. Simple broadcasts use flooding where every node in the network forwards the packet each time it is received. This creates broadcast redundancy. When nodes density in the network is high, more collisions and contentions are triggered as a result of redundant transmission. Furthermore network bandwidth is also wasted due to such redundant transmissions. This is a broadcast storm problem. In case of VANETs, congestion (e.g. congestion at junctions) intensifies the problem which may collapse the entire network. Ad hoc routing protocols like AODV  experience overhead and consume a large portion of bandwidth during route discovery, routing table updating and route error reporting phases. These protocols therefore, cannot be applied to VANETs.
1.4.1 Characteristics of VANETs
VANETs have some unique characteristics which make them different from MANET as well as challenging.
22.214.171.124 Highly dynamic topology
The topology of VANET changes frequently because vehicles move at a high speed.
126.96.36.199 Frequent disconnected network
Highly dynamic topology results in frequent disconnection occur between two vehicles when they are exchanging information. In sparse networks, disconnection occurs frequently.
188.8.131.52 Mobility modeling
The mobility pattern of vehicles is dependent upon traffic environment, roads structures, driverââ‚¬â„¢s driving behavior and the speed of vehicles.
184.108.40.206 Battery power
Vehicles have battery power that can be used for communication and processing.
1.4.2 Applications of VANETs
Examples of some of the VANET's applications are given below.
Cooperative assistance: distribution of data (warning of accidents).
Car-to-Mobile devices: applications used for communication between the car and mobile devices (e.g. mobile phone, laptop etc).
Car-to-Enterprise: communications between the car and companies (e.g. gas stations, restaurants, parking areas etc) which provide services on road.
Car-to-infrastructure: Hot spots send information to cars giving road and traffic information and car access to Internet etc.
Car-to-Car: exchange of information between car users such as files, traveling, chat, games and entertainment etc.
1.4.3 Categories of routing protocols in VANETs
Routing protocols in VANET can be categorized into following types :
220.127.116.11 Topology based routing
These protocols use route discovery process and maintain it in a table. The sender then starts transmitting data. These protocols are further divided into:
These protocols are also known as table driven routing protocols. These protocols periodically exchange the knowledge of topology among all the nodes of the network. These protocols consume a lot of bandwidth for periodic updates of topology. Proactive protocols monitor peer connectivity periodically to ensure the availability of any path amongst active nodes. Because these protocols periodically update topology information, a lot of band width is consumed. This makes them unsuitable for VANETs.
ââ‚¬Å“On demandââ‚¬ or reactive routing protocols were designed to overcome the overhead created by proactive routing protocols. These protocols maintain only those routes that are currently active. Routes are discovered as well as maintained for only those nodes that are currently being used to send data from source to the destination.
Route discovery in reactive routing is done by sending RREQ (Route Request message) from a source node when some data is to be sent to a particular destination. After sending RREQ, source node waits for the RREP (Route Reply) message. If it does not receive any RREP within a given time period, it is assumed that either route is not available or it is expired.
Reactive routing can either be source routing or hop-by-hop routing. In source routing, complete route information from source to destination is present in data packets. When these data packets are forwarded to other intermediate nodes in the network, each node uses route information present in the data packet. Here intermediate nodes do not need to update all route information in order to send packets to the destination.
However, main drawback of source routing is that it is not suitable for large scale networks. Further, these protocols do not have good performance in highly dynamic environment such as VANETs.
Hop-by-hop reactive routing works better than on demand source routing. Here each data packet contains next hop and destination addresses. Intermediate nodes from source to destination contain routing table information to send data packet to a destination. This is more helpful for accommodating sudden changes in topology. When topology changes nodes receives fresh routing table information and new routes are selected accordingly. The selected routes will now be used to send data packets to destination.
The Hybrid protocols
The design aim of hybrid protocols was to reduce the control overhead of proactive routing protocols and decrease initial route discovery delay in reactive routing protocols.
18.104.22.168 Position based protocols
These protocols make use of geographic positioning information to select the next hop.
Global route or hop-by-hop route between source and destination are created and maintained.
22.214.171.124 Geo-cast based protocols
These protocols are used to send messages to all vehicles present in a pre-defined geographical region.
126.96.36.199 Cluster-based routing protocols
In these routing protocols, vehicles in neighborhood of each other form a cluster. Each cluster has one cluster-head. The cluster-head is responsible for intra as well as inter-cluster management functions. Intra-cluster nodes can communicate each other via direct links. Inter-cluster communication is performed using cluster-heads. In cluster-based routing protocols, formation of clusters and the selection of the cluster-head is a critical issue.
188.8.131.52 Broadcast based protocols
These protocols use simple broadcasting to send data packets to destinations.
184.108.40.206 Infrastructure based protocols
These protocols are infrastructure based and use some infrastructure for routing. This means that routing in these protocols is not done in purely ad hoc mode.
1.5 Problem statement of the Thesis
Vehicular Ad hoc Networks (VANETs) are highly dynamic networks because of high mobility of vehicles. Highly dynamic network topology of VANETs hinders path determination as well as path maintenance process. High mobility of nodes results in more links breakages and degrades network performance in a proportionate way. This means that the frequency of change in topology is too high to determine a reliable path to the destination. This makes routing in VANETs a challenging task. This project addresses the routing issue in VANETs and proposes position and mobility parameter-based (PAMP) VANET routing protocol.
1.6 Aims and objectives
Aim of this research work is to develop an efficient routing protocol for VANETs and evaluate its performance in terms of different performance metrics.
1.7 Outline of the thesis
Chapter 2 discusses different VANET routing protocols. Here drawbacks of these protocols are also identified.
Chapter 3 gives the description of position and mobility parameters based (PAMP) VANET routing protocol. This chapter describes how the proposed will improve performance in terms of different performance metrics.
Chapter 4 is based upon simulation environment and performance analysis. It discusses simulation results in terms of different performance metrics.
Chapter 5 gives the summary of the research work and describes future work.