Wireless communication systems

This thesis presents the simulation based performance evaluation on the transmission of multimedia services (H.264/AVC video streaming) to a mobile user over a packet-switched wireless network based on the WCDMA standard. The H.264/AVC refers to the codec, which is used as the main tool for video compression. It enables the transport of high bandwidth video data over Third Generation (3G) wireless systems by offering a high video compression rate, adaptability to the channel, and error resilience. It is transported using the RTP/UDP/IP protocol stack over the 3G wireless system. The WCDMA technology is simulated with special emphasis on the upper layers of the wireless channel. The performance of the WCDMA system is studied when transporting RTP/UDP/IP packets of H.264/AVC compressed video data under diverse configuration scenarios, namely, ARQ schemes and variable length of the transmitted frame at the link layer. These components of a packet-switched streaming service are integrated into a software simulation model, which is used to evaluate the end-to-end H.264/AVC video quality in a WCDMA wireless network.

Wireless sensor networks are one of the first real world examples of pervasive computing, the notion that small, smart, and cheap sensing and computing devices will eventually permeate the environment. Sensor networks consist of very large number of energy constrained nodes and to properly evaluate these networks a scalable ad-hoc wireless network simulator with an energy model is needed. Since most of the existing simulators have been designed for ad-hoc network with low scalability they can not be used to accurately simulate sensor networks. The JiST/SWANS simulator is one of the newer simulators that has been developed by Cornell University for simulating ad-hoc networks and is highly scalable which makes it appropriate for use in evaluating sensor networks. Since this simulator lack energy model our objective is to design and implement an energy model for JiST/SWANS so that it can adequately and accurately calculate the amount of energy consumption in the simulation of sensor networks.

Peer-to-Peer (P2P) systems are characterized by direct access between peer computers, rather than through a centralized server. File sharing is the dominant P2P application on the Internet, allowing users to easily contribute, search and obtain content. The objective of this thesis was to design XYZ, a partially centralized, scalable and self-organizing lookup service for wide area P2P systems. The XYZ system is based on distributed hash table (DHT). A unique ID and a color assigned to each node and each file. The author uses clustering method to create the system backbone by connecting the cluster heads together and uses color clustering method to create color overlays. Any lookup for a file with a color will only be forwarded in the color overlay with the same color so that the searching space is minimized. Simulations and analysis are also provided in this thesis.

The security of wireless networks has gained considerable importance due to the rapid proliferation of wireless communications. While computer network heuristics and rules are being used to control and monitor the security of Wireless Local Area Networks (WLANs), mining and learning behaviors of network users can provide a deeper level of security analysis. The objective and contribution of this thesis is three fold: exploring the security vulnerabilities of the IEEE 802.11 standard for wireless networks; extracting features or metrics, from a security point of view, for modeling network traffic in a WLAN; and proposing a data mining-based approach to intrusion detection in WLANs. A clustering- and expert-based approach to intrusion detection in a wireless network is presented in this thesis. The case study data is obtained from a real-word WLAN and contains over one million records. Given the clusters of network traffic records, a distance-based heuristic measure is proposed for labeling clusters as either normal or intrusive. The empirical results demonstrate the promise of the proposed approach, laying the groundwork for a clustering-based framework for intrusion detection in computer networks.

In a beacon-enabled network, nodes send beacons when they are ready to transmit or receive messages from the other sensors in their communication range. If the beacons are not synchronized in time, a sensor might receive more than one beacon and hence will not be able to demodulate the beacon, thereby, being isolated from the network. As a result coverage nulls are introduced in the system. To address the above mentioned issues, Motorola Labs have proposed an algorithm for synchronizing the beacons in a wireless personal area network. In this thesis, extensive study of the proposed beacon time synchronization algorithm is done using OPNET as a simulation tool. Simulation is carried out by designing a detailed model of the algorithm using IEEE 802.15.4 as a reference. In depth analysis of the simulation results has been carried out. The results obtained are compared with those of existing time synchronization methods.

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.

This thesis describes QoS routing techniques in ad hoc networks. QoS routing is to find paths between given source and destinations that fulfill a set of QoS requirements. QoS routing in ad hoc networks is a challenging problem due to the dynamical nature of ad hoc networks and the complexity of the QoS routing problem. Ticket-based probing scheme (TBP) is a creative approach to solve QoS routing problem, however, its proactive nature makes it deficient and unscalable. In this thesis, we first present the adaptive ticket-based routing protocol (ATBR), a proactive protocol enhanced from TBP, by introducing a new imprecise QoS state model. We then present the location-aided, ticket-based routing protocol (LTBR), an integration of locate-based routing and ticket-based routing, where tickets are dynamically generated and guided by location and QoS metric. Our simulations show that, in networks under any density, LTBR achieves close performances to flooding with considerably lower routing overhead.

An ad hoc wireless network is a network composed of mobile communication devices, which is designed to provide communication capability to satisfy the need of a temporary nature in an infrastructure-less environment. A routing protocol is necessary in ad hoc networks to ensure effective communication among nodes. This thesis presents a simulation-based study on the performance evaluation of Ad hoc on-demand distance vector (AODV) routing protocol, which is one of the core routing protocols being promoted by the Mobile Ad Hoc Networking (MANET) group of the Internet Engineering Task Force. An event-advanced simulation program was developed in C++ to simulate the ad hoc wireless network implementing the AODV protocol. The performance metrics evaluated were throughput, average delay, route acquisition time and routing overhead. The network traffic was monitored in terms of the data packets created and successfully delivered within the simulation time. A discussion on the effect of different network parameters such as the mobility of the nodes, the number of nodes in the network, the size of the network and the data packet size on the performance characteristics of AODV protocol is also presented.

The objective of this work is to apply and investigate the performance of a neural network-based receiver for interference cancellation in multiuser direct sequence code division multiple access (DSCDMA) wireless networks. This research investigates a Receiver model which uses Neural Network receiver in combination with a conventional receiver system to provide an efficient mechanism for the Interference Suppression in DS/CDMA systems. The Conventional receiver is used for the time during which the neural network receiver is being trained. Once the NN receiver is trained the conventional receiver system is deactivated. It is demonstrated that this receiver when used along with an efficient Neural network model can outperform MMSE receiver or DFFLE receiver with significant advantages, such as improved bit-error ratio (BER) performance, adaptive operation, single-user detection in DS/CDMA environment and a near far resistant system.

In mobile ad hoc wireless networks (MANET), due to host mobility, broadcasting is expected to be frequently used to find a route to a particular host, to page a host, and to alarm all hosts. A straightforward broadcasting by flooding is usually very costly and results in substantial redundancy and more energy consumption. Power consumption is an important issue since most mobile hosts operate on battery. Broadcasting based on a connected dominating set (CDS) is a promising approach, where only nodes inside CDS need to relay the broadcast packet. Wu and Li proposed a simple distributed algorithm for calculating CDS in MANET. In general, nodes inside CDS consume more energy to handle various bypass traffics than nodes outside the set. To prolong the life span of each node and, hence, the network by balancing the energy consumption in the system, nodes should be alternated in being chosen to form a CDS. Activity scheduling deals with the way to rotate the role of each node among a set of given operation modes. In thesis I propose to apply power-aware CDS notions to broadcasting and activity scheduling. I also introduce distance rule and extended rules to further reduce broadcasting energy consumption. The effectiveness of the proposed method are confirmed through my simulation experiment.