An ad-hoc network is a packet radio network in which individual mobile nodes perform routing functions. Typically, an ad-hoc networking concept allows users wanting to communicate with each other while forming a temporary network, without any form of centralized administration. Each node participating in the network performs both the host and router function, and willing to forward packets for other nodes. For this purpose a routing protocol is needed. A novel approach utilizes the uniqueness of such a network i. e. distance, location and speed of the nodes, introducing a Distance Routing Effect Algorithm for Mobility (DREAM). The protocol uses the <i>distance effect</i> and the <i>mobility rate</i> as a means to assure routing accuracy. When data needs to be exchanged between two nodes, the directional algorithm sends messages in the recorded direction of the destination node, guaranteeing the delivery by following the direction. The improved algorithm suggested within this thesis project includes an additional parameter, direction of travel, as a means of determining the location of a destination node. When data needs to be exchanged between two nodes, the directional algorithm sends messages in the recorded direction of the destination node, guaranteeing the delivery by following the direction. The end result is an enhancement to the delivery ratio, of the sent to the received packet. This also allows the reduction in the number of control packets that need to be distributed, reducing the overall control overhead of the Improved Dream protocol.

Energy saving, despite recent advances in extending battery life, is still an important issue in wireless ad hoc networks. An often adopted method is power management, which can help in reducing the transmission power consumption and thus can prolong the battery life of mobile nodes. In this paper, we present a new approach of power management for the wireless ad-hoc networks. Firstly, we propose a clustering algorithm. The clustering algorithm is incooperated with power adjustment and energy-efficient routing procedure to achieve the goal of reducing the transmission power. We use clusterheads to monitor a mobile node's transmission power and to conduct the routing path between any source-destination pair. Not only the lifetime of network is increased but also the interference in communication channel is reduced. As a result, the transmission quality is improved and the network throughput is enhanced. By simulation, we showed that our algorithm outperforms the traditional clustering algorithm both in power saving and in throughput.

<p>TCP (Transmission Control Protocol) is a transport protocol designed for the wired Internet. In wireless networks packet losses occur more frequently due to the unreliability of the physical link. The main problem is that TCP treats all losses as congestion, which leads to a lower throughput. </p><p>Ad hoc networks are multihop wireless networks of mobile nodes, where each node can allow other packets to pass through it. Topology changes often occur and may lead to packet losses and delays, which TCP misinterprets as congestion. We want to modify TCP to recognize the differences between link failure and congestion to improve the capacity. </p><p>In our model we have built a connection in an ad hoc network where packet losses and partitions can be made. Simulation experiments show that we didn't get the problems we expected. This can be explained by low delays and because we buffered the packets during link failure. </p><p>A simple modification of TCP was made and simulated, and showed that an improvement of performance is possible. More research should be done to make a modification of TCP that would further affect the throughput.</p>

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Includes bibliographical references (p. 45-47).

published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

It has been envisioned that in the near future, wireless ad hoc networks would populate various application fields, ranging from disaster relief, environmental monitoring, surveillance, to medical applications, the observation of chemical and biological processes and community mesh networks. The decentralized and self-organizing nature of wireless ad hoc networks makes distributed algorithms fit very well in these networks, which however pose great challenges to the algorithm designers as they try to achieve optimal efficiency in communications. In this thesis, I develop a set of distributed algorithms addressing these challenges and solving some fundamental communication problems in wireless ad hoc networks. Communications in wireless ad hoc networks happen on a shared medium, and consequently are subject to interference. The first part of the thesis focuses on disseminating information on multiple-access channels while avoiding collisions. For both single-channel and multi-channel networks, the complexity of information dissemination is investigated, and nearly optimal distributed algorithms are proposed. The second part of the thesis focuses on designing efficient distributed algorithms for some fundamental problems under the physical Signal-to-Interference-plus-Noise-Ratio (SINR) interference model. The SINR model defines global fading interference with which the success of a signal reception depends on all simultaneous transmissions. Compared with graph based models, the SINR model reflects the fading and cumulative nature of radio signals. Hence, the SINR model represents the physical reality more precisely. However, the global nature of the SINR model makes the analysis of distributed algorithms much more challenging. Two types of fundamental problems are addressed in this part. The first type is closely related to communication coordination, including the wireless link scheduling problem and the node coloring problem. The second type of problems are about basic communication primitives, including the local broadcasting problem and the multiple-message broadcast problem. I investigate the complexity of these fundamental problems under the SINR interference model, and present efficient or optimal distributed algorithms. In the third part of the thesis, I propose a general interference model that can include commonly adopted interference models as special cases, and study whether efficient distributed algorithms can still be designed and analyzed in such a general model. Specifically, the affectance model is proposed in this part, which depicts the relative interference (affectance) on communication links caused by transmitting nodes. Both graph based models and the SINR model can be transformed into the affectance model. Under this general model, distributed algorithms with worst-case guarantees for the local broadcasting problem are presented. I also show how to make use of the developed techniques to get nearly optimal algorithms under the graph based model and the SINR model. / published_or_final_version / Computer Science / Doctoral / Doctor of Philosophy

In scuba diving any problem that can be solved underwater will be solved underwater. This helps to prevent a dive from being disrupted. If a diver is separated from the group and is unable to find the group within a short time both the diver and dive group must surface to find each other and rejoin. To prevent the separation of divers a Stray Diver Alert System has been devised involving wireless communication to track the diver's position relative to the dive masters. Underwater communication holds many challenges that are not found in above water networks. Through simulation, it has been shown that the communication requirements for the Stray Diver Alert can be met with existing technology and protocols. This has been done by evaluating the resolution, power consumption and physical size of the device for three different communication protocols. This has shown that current technology is capable of meeting the requirements of the stray diver alert system.

Peer-to-peer (P2P) applications are enormously popular on the Internet. Their uses vary from file sharing to Voice-over-IP to gaming and more. Increasingly, users are moving toward wireless networked devices and wish to continue using P2P applications in these new environments. A mobile ad hoc network (MANET) is an infrastructureless network which allows users to dynamically form a mobile, wireless network. Though P2P and MANETs share some similarities, such as self-organization, dynamism, and resilience to failure, it is necessary to create new P2P algorithms that take advantage of the realities of MANETs. These algorithms must account for the numerous challenges found in these networks, including node mobility, resource constrained nodes, and the necessity of fully distributed algorithms. In this thesis, we propose a framework for mobile P2P computing in MANETs (P2P-MANETs). Our proposal includes the following components. First, nodes must be able to locate and join the P2P overlay. We therefore propose a fully distributed bootstrapping algorithm in which nodes multicast join requests and cache responses. Next, the overlay peers must form a topology of connections between themselves. We propose a fully distributed topology control heuristic which supports the dynamic nature of the P2P-MANET. It is important that peers contribute to the network by sharing their resources and forwarding traffic for others. We therefore propose a dynamically priced incentive scheme which rewards users for contributing to the network. We also propose a path selection algorithm to allow peers to select how many parts of a file to download from which servers and which paths to satisfy the user's preference for download time and cost. Finally, we propose a content distribution system that allows users to download large files through the use of network coding and multicasting. Each of these components is the first proposed for its respective place in a P2P-MANET architecture. Simulation results show that each of the proposed components achieves the goals set out for it and outperforms the comparison schemes. The results also show that the overlay topology and path selection heuristics provide good approximations compared to the optimal solutions. / Thesis (Ph.D, Computing) -- Queen's University, 2010-01-27 12:16:25.352

Nowadays, with a worldwide market penetration of over 50% in the mobile telecommunications sector, there is also an unrelenting demand from the subscribers for ever increasing transmission rates and availability of broadband-like experience on the handset. Due to this, research in next-generation networks is rife. Such systems are expected to achieve peak data rates of up to 1 Gbps through the use of innovative technologies such as multiple-input and multipleoutput (MIMO) and orthogonal frequency division multiple access (OFDMA). Two more ways of boosting capacity have also been identified: shrinking cell sizes and greater reuse of resources in the same area. This forms the foundation of the research presented in this thesis. For operators, the costs involved with planning and deploying additional network infrastructure to provide a dense coverage of small, high capacity cells cannot be justified. Femto-cells, however, promise to fulfil this function. These are user-deployed mini base stations (BSs), known as home evolved NodeBs (HeNBs), which are envisaged to be commonplace in homes and offices in the coming years. Since they drastically reduce communication distances to user equipments (UEs) and reuse the resources already utilised in the macro-cell, they help boost the system capacity significantly. However, there are issues to be addressed with the deployment of femto-cells, such as increased interference to the system and methods of access. These and other problems are discussed and analysed in this thesis. One of the first steps towards femtocell research has been the study of the time division duplex (TDD) underlay concept, whereby an indoor UE acts as a relay between the evolved NodeB (eNB) and other indoor UEs. In order to gain a deeper understanding of how and under what conditions such a self-organising network can be deployed, a mathematical analysis of the distribution of path losses in a network of uniformly distributed nodes has been performed. In connection with this, research has also been done in the identification of well connected nodes in such networks. Next, extensive simulations on traditional cellular networks with embedded femto-cells have been carried out in order to demonstrate the benefits of femto-cell deployment. This research has shown that femto-cells can cause severe downlink (DL) interference to badly placed macro UEs. Finally, a novel interference avoiding technique that addresses this problem is investigated.