Mobile computing

Wireless ad hoc networks (or simply ad hoc networks) are infrastructureless multihop
networks consisting of mobile or stationary wireless devices, which include mobile
ad hoc networks (MANETs) and wireless sensor networks (WSNs). These networks are
characterized by limited bandwidth and energy resources, frequent topology changes,
and a lack of central control. These characteristics lead to the research challenges of ad
hoc networks. The algorithms designed for ad hoc networks should be localized, selforganizing,
and energy efficient. A connected dominating set (CDS) is frequently used in
ad hoc networks as a virtual backbone to support efficient routing, service discovery, and
area monitoring. In addition, efficient broadcasting (i.e., finding a small set of forward
nodes to ensure full delivery) can be viewed as forming a CDS on-the-fly. The periodically
maintained virtual backbone is called a static CDS, and the temporarily formed
forward node set is called a dynamk CDS. For efficiency and robustness, the ideal CDS
construction algorithm is lightweight, has fast convergence, and minimizes the CDS size. Recently, due to some specific applications and new techniques, the concept of a connected
dominating set can be modified or further extended for more efficient usage.
This dissertation focuses on the variations with applications of the connected dominating
set, designing new concepts, and developing new algorithms for them. A review
of CDS construction algorithms for ad hoc networks has been provided at the beginning.
An efficient scheme, called Rule K, has been proposed for static CDS construction. Rule
K achieves a probabilistic constant upper bound on the expected CDS size, which is currently
the best known performance guarantee for localized CDS algorithms. Several CDS
algorithms are extended to generate the extended CDS, which exploits the cooperative
communication technique to further reduce the size of CDS. A k-coverage set is developed
for higher robustness. With the equipment of directional antennas , the transmission
can be restricted to some certain directions to reduce interference and energy consumption.
The corresponding directional CDS is discussed. Finally, a wireless sensor and actor
network (WSAN) is introduced and localized algorithms are designed for it.

With the explosive growth of the Internet and other types of networks, such as cell phones and pager networks, more and more people expect to communicate with each other personally anywhere and at anytime. This thesis studies a new architecture Mobile People Architecture (MPA) proposed by MosquitoNet research group at Stanford University, which is designed to put people, rather than the devices that people use, at the endpoints of communication session. Three usage scenarios in MPA are simulated using SES/Workbench. The Response Time and the Update Cost are used to evaluate the performance of above scenarios. The advantages and disadvantages of different scenarios are also analyzed and discussed in this thesis.

In the present computer age, cellular technology and portable computers are becoming an integral part of the life. Each computer user wants to access the computing resources, irrespective of the location. Because of this need the computing paradigm "Mobile Computing" has assumed a primary role in modern computer communication technology. While dimensioning the network resources, it is very important to know how the users move around the geographical area covered by the cellular network. This knowledge allows us to plan the system resources in order to achieve the QoS required. The major factors that affect the performance, along with the mobility pattern of the mobile user, are the speed at which the user is moving and the load on the network. In this research, we study different types of mobility patterns the user can follow and it's impact on the network services. We have proposed and evaluated a reservation scheme to improve the QoS in the cellular network. The reservation scheme reserves some part of the bandwidth for handoff connections. We have developed simulation programs and have studied three mobility patterns namely leading movement type, random motion, and square-street mobility pattern for measuring the QoS for cellular network. It has been observed from the results that at an average speed of 50 miles per hour with the average loading of the network, a significant improvement in QoS has been achieved for all the mobility patterns by using the reservation scheme.

This thesis describes routing in mobile ad hoc wireless networks. Ad hoc networks are lack of wired backbone to maintain routes as mobile hosts move and power is on or off. Therefore, the hosts in ad hoc networks must cooperate with each other to determine routes in a distributed manner. Routing based on a connected dominating set is a frequently used approach, where the searching space for a route is reduced to nodes in small connected dominating set subnetwork. We propose a simple and efficient distributed algorithm for calculating connected dominating set in a given un-directed ad hoc network, then evaluate the proposed algorithm through simulation. We also discuss connected dominating set update/recalculation algorithms when the topology of the ad hoc network changes. We also explore the possible extension of using hierarchical connected dominating set. The shortest path routing and the dynamic source routing, which are based on the connected dominating set subnetwork, are discussed.

In this present computer age, cellular technology and portable computers are becoming an integral part of day to day life. Each computer user wants to access the computing resources, irrespective of the location. Because of this need the computing paradigm "Mobile Computing" has assumed a primary role in modern computer communication technology. There are different Internet protocols proposed for Mobile Computing. In the present research, we study the Internet Engineering Task Force (IETF) Mobile IPv6 (new version of current IPv4 protocol). We have developed simulation program using Scientific and Engineering Software (SES/workbench) and studied three mobility patterns namely Travelling Salesman, Pop-Up and Boring Professor for the performance study of Mobile IPv6. Performance of Mobile IPv6 is measured in terms of utilization and overhead and compared with Mobile IPv4 and Basic Triangular Routing (BTR). It has been observed that Mobile IPv6 scheme has better route optimization than the other schemes when Mobile node's movement from one network to another network is less frequent. But, when the movement of the Mobile node is more frequent then Basic Triangular Routing scheme outperformed the Mobile IPv6 scheme.

With the advent of cellular technology and portable computers we are on the verge of a new computing paradigm. This computing paradigm is now widely known as "mobile" or "nomadic" computing. Mobile systems frequently change their point of attachment to the network. Mobile computing systems also need to communicate with the existing pool of information and file servers. Mobility defies the very principles that the TCP/IP protocol suite is based on. We study the Internet Engineering Task Force (IETF) Mobile IPv4 protocol and find it to be a highly scale solution. We study some of the other proposed mobile IP solutions. We establish a criterion, call-to-mobility ratio, to compare various mobile IP schemes. Two hypothetical schemes, Static Update and Triangular Routing, are introduced solely for the purpose of comparing the performance of Mobile IPv4. In our simulation we concentrate on calculating the update costs and the routing costs for Triangular Routing, Static update and Mobile IPv4 schemes. The simulation program to simulate Triangular Routing, Static Update and Mobile IPv4 is written in C++. Minetsim, our simulation program is written using object-oriented analysis and design. Minetsim is used to obtain routing and update costs for Triangular Routing, Static Update and Mobile IPv4 schemes. Four different host configurations are simulated for travelling salesman and random motion mobility models.

In this thesis, a delta service extends a mobile file system cache in order to minimize the amount of data transferred over wireless communications links. Network bandwidth stands as one of the resource limitations impacting the design of mobile computer applications. At the mobile file system service level, caching and compression provide resource conservation in distributed applications. This thesis proposes a delta service to enhance caching services characteristic of mobile computer file systems. Well established a mechanisms for sequence comparison and software configuration management, file deltas have applicability to mobile computer and distributed file system caching environments. Study of the delta service uses trace-driven simulation methodology incorporating traces obtained in a real world distributed environment. A mobile computer client cache model will corroborate existing studies regarding suitable cache size for disconnected client operation. A delta service model will extend the mobile computer client cache model of various cache sizes in order to gauge the bandwidth savings on the link obtained by the delta service.

Compared to the traditional wireless network, the multi-hop ad hoc wireless network (simply called ad hoc networks) is self-configurable, dynamic, and distributed. During the past few years, many routing protocols have been proposed for this particular network environment. While in wired and optical networks, multi-protocol label switching (MPLS) has clearly shown its advantages in routing and switching such as flexibility, high efficiency, scalability, and low cost, however MPLS is complex and does not consider the mobility issue for wireless networks, especially for ad hoc networks. This thesis migrates the label concept into the ad hoc network and provides a framework for the efficient Label Routing Protocol (LRP) in such a network. The MAC layer is also optimized with LRP for shorter delay, power saving, and higher efficiency. The simulation results show that the delay is improved significantly with this cross-layer routing protocol.

Wireless Internet access has recently gained significant attention as wireless/mobile communications and networking become widespread. Voice over IP service is likely to play a key role in the convergence of IP based Internet and mobile cellular networks. The mobility management performance for Mobile IP and Session Initiation Protocol is the focus of this thesis. After illustrating the operation of the protocols, the discrete event simulator, Network Simulator 2 (ns2), is used to compare the performance of the two protocols. The comparison of the protocols is done by comparing average end-to-end delay and the ratio of the number of packets received to the number of packets originally sent (Packet Delivery Fraction). The impact of mobility is analyzed by studying the performance of the protocols, for various mobility scenarios. The effect of an increase in the number of nodes and increase in velocity of the mobile node on the performance of the Mobile IP and SIP is compared. The performance of the Mobile IP and SIP is compared by measuring the performance metrics of the two protocols for similar simulations. The results obtained as a result of the simulations leads us to some interesting conclusions.

The ad hoc wireless network is an infrastructureless network, where mobile stations are typically powered by batteries. Energy conservation has therefore becomes a very important issue. In this thesis, we discuss our work on several problems in energy-efficient routing. Chapter 3 focuses on how to compute the minimum uniform broadcast transmission power in an ad hoc wireless network. Several algorithms are proposed and their running time compared through simulation. It is shown that Prim's Minimum Spanning Tree (MST) has better performance than Kruskal's MST and the two binary search algorithms. In the following two chapters, routing algorithms are studied for specific situations, when directional antenna is used (Chapter 4) or when partial signal could be collected, stored and integrated (Chapter 5). Different algorithms are discussed and their energy performance illustrated by simulation study. Their application and limitation are also discussed in the thesis.