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CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

A Mobile Ad hoc Network is a collection of wireless mobile nodes

forming a temporary network without any infrastructure or centralized

administration. It is a multi-hop network with a routing path composed of a

number of intermediate mobile nodes and wireless links connecting them.

Nodes are assumed to move freely and hence the routes are prone to fail from

time to time.

There are several wireless network technologies such as WiFi,

GSM, UMTS and WiMAX. When multiple networks integrate, they will

work together to provide better services for users. The goal is to guarantee

network connectivity, reduced call drop rate, good signal strength and

delivery of predictable results in a stipulated time frame. An incorrect handoff

decision (Haider et al 2012) during the mobile crossing the boundaries of the

coverage region between two Base Stations may degrade QoS and even break

off current communication. Thus, it is important that handoffs be carried out

smoothly and accurately for improved QoS.

Hence there is a need for a solution to provide a reliable and

opportunistic communication path, by choosing nodes that can provide

maximum network lifetime. The opportunistic networking idea stems from

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the critical review of the research field on Mobile Ad hoc Networks

(MANET).

1.2 INTRODUCTION TO OPPORTUNISTIC NETWORKS

The opportunistic communication scenario is demonstrated as

shown in Figure 1.1. The setup considers the heterogeneous environment

equipped with infrastructure less networks termed as MANET and

infrastructure based networks like WiFi, WiMAX , etc., The source node can

be a member of the MANET which sends information to a destination node,

that can be a member in the same MANET or different MANET or under the

coverage region of the base station in the mobile network.

Figure 1.1 Opportunistic Communication Scenarios

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The various definitions are as follows:

Opportunistic Networks: An opportunistic network is a

network of wireless connected nodes which may be either

mobile or fixed. Communication range between two connected

nodes is within walking distance, i.e., 100 300 meters. The

network topology may change due to node mobility (Camp et al

2002) or node activation and node deactivation. The nodes

provide the following functionality:

Node Discovery: A network node is able to discover other

network nodes in direct communication range.

One-hop Message Exchange: A node is able to send and

receive arbitrary data in form of a message to or from any

other node in direct communication range.

Opportunistic networks also aim at building networks out of mobile

devices carried by people, possibly without relying on any pre-existing

infrastructure. However, opportunistic networks look at mobility,

disconnections, partitions, etc. as features of the networks rather than

exceptions. Actually, mobility is exploited as a way to bridge disconnected

dealt with. More specifically, in opportunistic networking no assumption is

made on the existence of a complete path between two nodes wishing to

communicate. Source and destination nodes might never be connected to the

same network, at the same time. Nevertheless, opportunistic networking

techniques allow such nodes to exchange messages. By exploiting the store-

carry-and-forward paradigm, intermediate nodes (between source and

destination) store messages when no forwarding opportunity towards the final

destination exists, and also exploit any future contact opportunity with other

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mobile devices to bring the messages closer and closer to the destination. This

approach to build self organising (Dressler 2008) infrastructure less wireless

networks turns out to be much more practical than the conventional MANET

paradigm. Indeed, despite the fact that opportunistic network research is still

in its early stages, the opportunistic networking concept is nowadays

exploited in a number of concrete applications.

The opportunistic networks govern the following characteristics:

They are extensions of the infrastructure that will comprise

various devices and terminals (envisaged in the Future Internet),

potentially organized in an infrastructure-less mode, as well as

elements of the infrastructure.

They will exist temporarily, i.e. for the time frame necessary to

support particular applications requested in specific location and

time. Applications can be related to the social networking,

military communication services, medical, etc.

1.3 MANET VS OPPORTUNISTIC NETWORKS

This section compares the MANET and the opportunistic networks.

MANET

MANET (Royer & Toh 1999) often aims at synchronous

communication between two nodes.

MANET routing is Multi hop and real time

MANET (Carlo Kopp 1999) assumes everyone wants to

contribute

Mostly all nodes will be willing to route traffic

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Sample application domains: Military, sensor networks, rescue

scenarios

Key characteristic: Common goal, strong relationship

Opportunistic Networks (OPPNETs)

OPPNETs are usually asynchronous in Communication (Pelusi

et al 2006)

It exploits human mobility to move information

One-hop communication to share information

augmented with constrained propagation based on user profiles

mimics word-of-mouth communication between humans

The broad distinguishing terms among MANET and Opportunistic

networks are shown in Table 1.1.

Table 1.1 MANET Vs Opportunistic Networks

Network Type

Routing/ Message

Forwarding

Node Mobility

Network Size

Community Dynamics

Node Relationship

MANET

Yes Yes Low

medium Medium High

Opportunistic Network

Yes Yes High Medium Low

In order to provide a communication path where sufficient

infrastructure may not be possible, human intelligence can be used to provide

a feasible service. In a scenario where there is no possible coverage for links,

an opportunistic way of connecting nodes can be implemented by multi hop

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approach. It can be integrated further with the heterogeneous network

environment to satisfy the need of the user, data and the application. In order

to accomplish this, MANET is chosen to integrate with infrastructure based

cellular network.

This thesis proposes a solution for reducing the energy

consumption in mobile nodes by using the vertical handoff decision

algorithms, so that the battery operation time (Chansu YuBen et al 2003) of

the wireless terminal is maximized and the network resource is utilized

efficiently to meet the QoS.

1.4 APPLICATIONS OF OPPORTUNISTIC NETWORKS

The following applications domains are listed as follows:

Military communication services: OPPNETs can be very

useful in establishing communication among a group of soldiers

for tactical operations. Setting up a fixed infrastructure for

communication among a group of soldiers in enemy territories

or in inhospitable terrains may not be possible. In such

environments, ad hoc wireless networks can provide the

required communication (Mills 2007) mechanism quickly.

Another application area could be the coordination of military

objects moving at high speeds like fleets of airplanes or

warships. Such application requires quick and reliable

communication. Secure communication is of prime importance

to eavesdropping or other security threats that can compromise

the purpose of communication or the safety of personnel in

these tactical operations. They also require the support of

reliable and secure multimedia multicasting. For example the

leader of a group of soldiers may order all the soldiers or set

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some of selected personnel involved in the operation. Hence the

routing protocol in these applications should be able to provide

quick, secure, and reliable communication in real-time traffic

(Siva Ram Murthy & Manoj 2007).

Tele-medicine: Opportunistic computing and network

technologies can be used to create a pervasive system of

intelligent devices comprising sensors and actuators that

embrace patient surroundings at different levels. Transparently

embedded body area networks and sensors can cooperatively

gather, process, and transport information on our lifestyle and

the social and environmental context around us without

requi

Opportunistic networking techniques can be deployed as basic

tools in distributed context-aware pervasive applications

(Osianoh Glenn Aliu et al 2012) for performing real,

noninvasive, continuous multi-parametric monitoring of

physical and physiological parameters.

Disaster managements: OPPNETs are very useful in

emergency operations such as search and rescue, crowd control,

and commando operations. In environments where the

conventional infrastructure based communication facilities are

destroyed due to a war or due to natural calamities such as

earthquakes, immediate deployment of these networks require

minimum initial network configuration (Kalamazoo et al 2007)

for their functioning. In that case, very little or no delay is

involved in making the network fully operational. The above-

mentioned scenarios are unexpected; in most cases unavoidable,

and can affect a large number of people. OPPNETs employed in

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such circumstances need to distributed and scalable to a large

number of nodes. They should also be able to provide fault-

tolerant communication paths. Real-time communication

capability is also important as voice communication

predominates data communication in such situations.

Infomobility services and intelligent transportation systems:

Vehicular ad hoc networks (VANETs) exploit vehicle-to-

vehicle communications, as well as the communication with

roadside infrastructure, to implement cooperative systems and

to increase traffic efficiency and safety. Other applications

include tourist information and assistance such as parking

availability notification and maps, and entertainment such as

gaming and streaming video.

1.5 HETEROGENEOUS WIRELESS NETWORKS

Next generation wireless networks should allow the coexistence of

different access technologies and provide the differentiated services to end

users. However, the provisioning of differentiated services over

heterogeneous networks poses several challenges. The existing heterogeneous

networks namely IEEE 802.11g (WiFi), IEEE 802.16d/e (WiMAX) and

3GPP2 LTE have their own advantages in terms of characteristic such as

coverage-region, data-rate and broadband services. The network system

architecture of WiFi, WiMAX and LTE are as shown in Figure 1.2, Figure 1.3

and Figure 1.4 respectively.

1.5.1 IEEE 802.11 WiFi (Wireless Fidelity)

Wi-Fi (Wireless Fidelity) has standardized from IEEE 802.11 a, b,

and g. Wi-Fi is the first widely deployed fixed broadband wireless networks

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with a maximum data rate of 54Mbps. The Wi-Fi architecture (Deep Kaur &

Vishal Arora 2013) consists of a base station to which wireless hosts connect

in order to access the network resources. As long as the users remain within

300 feet of the fixed wireless access point, they can maintain broadband

wireless connectivity. It has short range of coverage and hence suitable only

for indoor services. Figure 1.2 shows IEEE 802.11 WiFi.

Figure 1.2 IEEE 802.11 WiFi

1.5.2 IEEE 802.16 WiMAX

WiMAX (Wireless Interoperability for Microwave Access)

eliminates the constraints of WiFi in terms of coverage. Unlike WiFi,

WiMAX is intended to work outdoors over long distances. It is a more

complex technology and has to handle critical issues such as guarantee QoS,

carrier-class reliability, NLOS, etc. WiMAX is not intended to replace Wi-Fi

in order to provide broader coverage. Instead, the two technologies

complement each other. WiMAX covers 50 km radius with speed up to

70 Mbps. The objectives of WiMAX are superior performance, flexibility,

advanced IP-Based architecture, attractive economics. WiMAX can provide

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at-home or mobile Internet access across whole cities or countries. Figure 1.3

shows IEEE 802.16 WiMAX (Md. Alimul Haque et al 2011).

Figure 1.3 IEEE 802.16 WiMAX

1.5.3 3GPP Release-8 LTE

LTE (Long Term Evolution) is a standard for wireless

communication of high-speed data for mobile phones and data terminals. It is

based on the GSM / EDGE and UMTS / HSPA network technologies, that

increases the capacity and speed by using new modulation techniques. The

standard is developed by the 3GPP (3rd Generation Partnership Project). The

goal of LTE is to increase the capacity and speed of wireless data networks.

The data type is all packet switched data for both voice and data. The

applications of LTE are voice, SMS, instant messaging, internet browsing,

video streaming, social networking, online navigation, email, health

surveillance, vehicle tracking, positioning and tracking. Figure 1.4 shows

LTE.

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Figure 1.4 Long Term Evolution (LTE)

Figure 1.5 shows the LTE network architecture in detail. It supports

the data rate of 300 Mbps (DL)/75 Mbps (UL) with less than 5ms latency.

Mobility Management Entity (MME) has functionalities such as

identification, authentication, attach and detach procedures.

Figure 1.5 LTE-Network System

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HSS (Home Subscriber System) maintains the subscribers fixed

information. Serving Gateway handles policy and charging rule functions.

PDN Gateway bridges the user (UE) and different external IP networks.

eNodeB - Evolved NodeB is similar to node B in UMTS network functioning

as base station. Evolved Packet Core or System (EPC)/EPC handles the

network side responsibilities.

1.6 NEED FOR VERTICAL HANDOVER

Future generation wireless networks are expected to support

heterogeneous access technologies such as WiFi, WiMAX, LTE, etc., than

homogeneous wireless networks (Tansir Ahmed et al 2006). The present trend

towards ubiquity of network, global mobility and network access is provided

by a large diversity of technologies with coverage overlaps. The new mobile

devices not only provide the user with great flexibility for network access and

connectivity, but also create a challenging problem of mobility support among

different networks. Users will expect their connections to be without any

disruption when they move from one network to another.

In heterogeneous wireless network environment (Yang & Chuah

2006), the always best connected (ABC) service requires dynamic selection of

the best network and access technologies when multiple options are available

simultaneously. An important process in wireless networks is referred to as

handoff or handover. In cellular telecommunications, the term handover or

handoff refers to the process of transferring an ongoing call or data session

from one channel connected to the core network to another. Handover refers

to the automatic switching from one technology to another in order to

maintain communication. This handoff technology is needed for seamless

mobility and uninterrupted connectivity.

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1.6.1 Types of Handover

Figure 1.6 shows the different basic handover scenarios. The

handover takes place under two different situations, when user moves from

one location to another i.e. mobility and the other situation is heavy network

load condition. The process of transferring an ongoing call or data session

from one base station to another base station without loss or disruption of

service is known as handoff or handover. The basic two different types of

handovers are horizontal and vertical handovers are explained as follows:

Horizontal handover - the users use the same network access

technology and the mobility is performed on the same layers. In

horizontal handover the on-going calls are to be maintained in

spite the change of IP address because of the mobile node

movement.

Vertical handover - the user can move across different network

access technologies (Singhnova & Prakash 2012). The change is

not only in the IP address but also in the network interface, QoS

characteristics etc.

Figure 1.6 Horizontal and Vertical Handover Scenarios

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1.6.2 Handover Management System

In heterogeneous wireless networks, handoff can be separated into

two parts: Horizontal handoff (HHO) and Vertical Handoff (VHO). A

horizontal handoff is made between different access points within the same

link-layer technology such as when transferring a connection from one BS to

another or from one AP to another. A vertical handoff (KavehShafee et al

2011) is a handoff between access networks with different link-layer

technologies. The comparison between horizontal and vertical handover

schemes is shown in Table 1.2.

Table 1.2 Vertical Vs Horizontal Handovers

Vertical Handover Horizontal handover

Access Technology Changed Not changed

QoS Parameters May be changed Not changed

IP Address Changed Changed

Network Interface May be changed Not changed

Network connection

More than one connections

Single connection

During the handoff decision phase, the mobile device determines

the network to which it should connect. During the handoff execution phase,

connections are re-routed from the existing network to the new network in a

seamless manner. During the VHO procedure, the handoff decision is the

handoff decision may degrade the QoS of traffic (Tao Yang & PengRong

2011) and even break off current communication.

The basic idea of handoff is to effectively use the network

bandwidth and provide improvised QoS to real-time applications (Xu et al

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2003). Some of these modules collect the link-layer and network-layer

information useful for handoff management, and other modules use this

information to decide on the appropriate time to initiate handoff and execute

the handoff procedures. This approach is called cross-layered handover.

If there are multiple network choices, and the current access

network cannot satisfy the QoS requirements (Lin & Liu 1999) of the existing

applications, the handoff decision module will be started. It will determine the

destination network based on the staying time of the MH in the candidate

network and QoS estimation which including RSS, channel utilization, link

delay, jitter, etc. Based on the output of the handoff decision algorithm, the

system will choose either the VHO routine or the HHO routine to hold the

current connection.

1.7 RESEARCH ISSUES IN OPPORTUNISTIC

COMMUNICATION

Opportunistic networks combined with social computing, herald the

new paradigm of opportunistic computing for pervasive applications.

Whereas pervasive computing seeks to enhance user quality of life through

proactive application services, opportunistic computing also recognizes and

User devices, and indeed their BANs/PANs,

possess complementary capabilities in terms of computing, communication,

storage, energy, sensing, and related applications (Srivastava & Motani 2005).

This opens several research issues for developing a set of middleware services

that mask disconnections and heterogeneities which provide the applications

with uniform access to data and services in a disconnected environment.

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1.7.1 Middleware Services

Middleware services provide mechanisms for managing

information and access through a variety of applications, such as data and

services placement, resource management (for example, storage, bandwidth,

and energy), trust, security, and privacy for opportunistic computing, mobile

agents, remote execution, and cyberforaging, among others. Trust and data

privacy pose key issues. For example, reputation mechanisms should be in

place to detect malicious users who might join a group to thwart collective

actions or acquire sensitive information (Welch et al 2003).

mechanism to increase efficiency and security. Novel mechanisms for service

sharing in a disconnected environment must be devised. Developing modular

tools for message passing, information dissemination and acquisition,

resource management, service discovery, service management, and other tasks

poses a huge challenge to heterogeneous opportunistic environments. Fault

tolerance is critical to many distributed computing applications. While most

current work assumes the existence of local networks, not much research has

been done in the prevention, detection, and recovery aspects of faults in

challenged environments. Collaboration in opportunistic environments calls

for new, robust strategies that facilitate collaboration in the absence of

continuous connectivity. Mechanisms for replication and redundancy must

take into consideration the limited resources in such constrained systems.

Application tasks executing on one device will be required to interact with

resources and services on other devices under time and connectivity

constraints.

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1.7.2 Information Management

In an opportunistic computing environment, special attention must

be dedicated to information management and provisioning because a vast

range of information is embedded in the environment of pervasive computing

and communication systems. However, the use of opportunistic techniques to

provide situated information has not yet received much attention, even though

there are developments of significant relevance in the distribution of content

within P2P systems. Many developers have considered the extension of

Internet-based content sharing systems to mobile ad hoc networks by

overlaying the P2P structure. However, very little development has taken

place for P2P information provision in opportunistic networking.

The lack of distinction between information producers and

consumers on one hand and the utilization of opportunistic contacts to

disseminate and acquire them on the other makes this task challenging.

Aggressive broadcasting mechanisms, such as those based on epidemic

dissemination protocols, have a tendency to load the network, abusing contact

capacity and the content cache. From an information-centric perspective, use

of opportunistic networks for information provision results in three

fundamental issues: determining what to store, where to store it, and how to

acquire relevant information.

1.7.3 Context Awareness

Context awareness is a relevant key for searching the network.

First, most of the content is relevant for people physically close to the source,

who thus form a transient, local community with which to interact jointly.

This requires establishing dynamic and temporary trust relationships between

humans and machines. In addition, part of the generated content will be of

interest to other users in virtual communities, which share common interests

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irrespective of their physical location. This means that a much wider range of

objects can generate and store information while situated in an environment.

Context information and profiles of devices, individuals, and applications

together with cache optimization techniques are needed for the effective

management of the content cache. To share information within a social

environment, researchers have proposed social caches.

A social cache is a logical collective view of individual device

caches that cache information objects useful to the members of its social

group. Given that members are expected to meet more frequently, and

information in the social cache can be effectively utilized by many members,

social caching can significantly increase system performance.

1.7.4 Services, Data Placement and Replication

In an opportunistic computing environment, applications need

different kinds of resources to execute services, and such resources may be

available within the network. Similarly, user devices and sensors carry or

supply different kinds of information that is useful to other users and

applications.

social communities. Therefore, to increase system efficiency, it is critical to

make services and data available in the environment closer to users who need

them. Replication of data or services increases their availability, while their

migration may reduce the access delay (Nam et al 2004). While placement of

services is a well-investigated problem in traditional distributed systems,

dynamic pervasive environments, such as those created by opportunistic

contacts, pose new challenges.

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1.7.5 Resource Management

contact capacity, should be used effectively. The capacity is limited and

varies in accordance with wireless communication conditions and the

mobility (Akyildiz et al 1999) of devices and their users. The contact capacity

should be utilized effectively to ascertain reputations, establish trust,

collaborate, and exchange information between the two meeting devices and

their users.

The second most important resource is the memory or buffer space

in the devices termed as content cache. In opportunistic computing, devices

carry should be

optimally maintained by purging unwanted data and keeping data useful to

the applications on the device, such as peers it expects to meet in the near

future. The content cache can be tuned to certain applications, contexts, or

other criteria.

Energy (Shio Kumar Singh et al 2010) is another key resource for

an opportunistic environment, in which most devices are battery enabled.

Energy management is a cross-layer issue (Salawu & Onwuka 2009) with

respect to the management of storage and bandwidth. Increased data

transmission on the wireless interface results in more energy spent, while

local data storage might incur significant energy costs for memory

management.

Finally, the hardware and software resources on the devices must

be exploited by providing seamless accessibility to applications executing on

other devices. As most devices in opportunistic networks are mobile, they

possess limited and varied hardware and software resources. Using resources

distributed across the devices in a given space, such as a social network, is

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critical. Matching services to resources in opportunistic networks presents

another challenge.

1.7.6 Trust, Security and Privacy

Establishing trust and security (Tseng et al 2003) for an interaction

between a priori unknown peers in an opportunistic network is challenging.

However, social network structures offer a basis to enhance trust and security

between them, either physically or logically.

The idea of using social network structures and properties for

enhancing network security (Mishra et al 2004) is not novel. Indeed, the

literature contains several proposals based on using social networks to fight e-

mail spam and defend against attacks. However, the use of social networks in

completely decentralized networks is a completely new and challenging task

because, in such an environment, legacy security solutions based on

centralized server or online trusted authorities becomes infeasible. In this

case, a natural direction to pursue exploits electronic social networks and the

trust and security relationships naturally embedded in human interactions.

1.7.7 Economic Model and Social Cooperation

A solid economic model is fundamental to justifying

implementation of an opportunistic computing paradigm. Why should one

user make computing resources available to another? This is an even more

critical question when the computing platforms are mobile devices that have

very limited and critical resources, such as energy.

The development of an economic model to stimulate cooperation

among peers has been extensively discussed in the framework of both P2P

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platforms and mobile ad hoc networking, where solutions based on incentives

or reputation have been devised. Similar strategies can probably be applied

here. However, exploiting the natural cooperation that exists in human social

relations is the catalyst for opportunistic computing. In principle, rational

users gain the most from an uncooperative behavior but, despite this, human

society often exhibits cooperative behaviors. Characterizing and enforcing

human cooperation is highly relevant for electronic social networks.

1.7.8 Mobile Agents, Remote Execution and Cyber Foraging

In an opportunistic computing environment, services are often only

available on remote nodes outside direct communication of the requesting

device. This requires developing mechanisms to support the remote execution

of tasks and return the results to the node(s) requesting a service. Mobile

agent technology can be an effective tool to address this issue. Mobile agents

may migrate from one node to another during contacts, carry input data and

code, and exploit services and resources in the visited nodes. When a task

execution is completed, these agents return to the source node together with

their results. Similarly, mobile agents can be employed for information

acquisition and dissemination.

1.8 RESEARCH CHALLENGES AND OBJECTIVES

This section describes the challenges and objectives of this thesis

towards opportunistic communication.

1.8.1 Multihop Routing and Vertical Handover Challenges

MANETs are infrastructure-less networks and hence reliable

communication paths do not exist readily. The crucial challenges (Satyabrata

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Chakrabarti & Amitabh Mishra 2011) that necessitated opportunistic

networks are as follows:

Do not depend on a permanent backbone.

Unreliable links and entities.

Prone for failure and degradation.

Limited resources such as battery, bandwidth etc.

Dynamic topology changes due to mobility of the nodes.

Infrastructure based wireless network consists of Base Stations of

different technologies such as WiFi, WiMAX etc., Few issues are

Handoff

Bandwidth and Data rate

Mobility level and energy level

1.8.2 Research Objectives

The main objectives of this work are as follows

To find an enhanced multihop path, by choosing trusted nodes

with maximum energy level using human mobility prediction in

the MANET environment.

To focus on linking the MANET with appropriate access

technology in the heterogeneous network using link nodes that

acts as a gateway.

To focus on the problem of resource management in

heterogeneous wireless network by Vertical Handover decisions

based on network parameters and user preferences.

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To deliver the message from heterogeneous network to the

destination node if it exists in the MANET using gateway node.

1.9 ORGANIZATION OF THE THESIS

The thesis is organized is as follows:

Chapter 2 presents the literature survey pertaining to existing

multihop routing and vertical handover issues. The existing issues and its

performance metrics related to opportunistic networks are listed out in this

chapter.

Chapter 3 describes the framework constructed for opportunistic

communication. It considers the enhanced multihop routing and vertical

handover decision modules in order to provide the effective opportunistic

communications.

Chapter 4 presents the enhanced multihop routing based on trust,

mobility patterns and energy levels. Then the opportunistic communication

path is computed based on TME (Trust-Mobility-Energy) parameters and the

results are explained in this Chapter.

Chapter 5 presents the research contributions relating to the

implementations of Vertical Handover Decision in heterogeneous

environments. The score-based vertical handover decision is made based on

the estimated score values of RSS, velocity and bandwidth. The service

history based handover decision also considered. The fuzzy based relational

handover decision is made based on enhanced approaches of SAW, TOPSIS

and AHP are presented in this Chapter.

Chapter 6 describes the performance analyses of enhanced

multihop routing with its results and discussions.

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Chapter 7 describes the performance analyses of efficient handover

decision with its results and discussions are compared.

Chapter 8 gives the conclusion of the thesis and the scope for future

research in this area.