Modem technology has revived interest in the once popular area of meteor scatter communications. Meteor scatter systems offer reliable communications in the 500 to 2000 km range all day, every day. Recent advances in microprocessor technology have made meteor scatter communications a viable and cost effective method of providing modest data rate communications. A return to the basic fundamentals has revealed characteristics of meteor scatter propagation that can be used to optimize the protocols for a meteor scatter link. The duration of an underdense trail is bounded when its initial amplitude is known. The upper bound of the duration is determined by maximizing the classical underdense model. The lower bound is determined by considering the volume of sky utilized. The duration distribution between these bounds is computed and compared to measured values. The duration distribution is then used to specify a fixed data rate, frame adaptive protocol which more efficaciously utilizes underdense trails, in the half duplex environment, than a non-adaptive protocol. The performance of these protocols is verified by modeling. / Thesis (Ph.D.)-University of Natal, Durban, 1987.

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Network virtualization is becoming a fundamental building block of future Internet architectures. By adding networking resources into the “cloud”, it is possible for users to rent virtual routers from the underlying network infrastructure, connect them with virtual channels to form a virtual network, and tailor the virtual network (e.g., load application-specific networking protocols, libraries and software stacks on to the virtual routers) to carry out a specific task. In addition, network virtualization technology allows such special-purpose virtual networks to co-exist on the same set of network infrastructure without interfering with each other. Although the underlying network resources needed to support virtualized networks are rapidly becoming available, constructing a virtual network from the ground up and using the network is a challenging and labor-intensive task, one best left to experts. To tackle this problem, we introduce the concept of a HyperNet, a pre-built, pre-configured network package that a user can easily deploy or access a virtual network to carry out a specific task (e.g., multicast video conferencing). HyperNets package together the network topology configuration, software, and network services needed to create and deploy a custom virtual network. Users download HyperNets from HyperNet repositories and then “run” them on virtualized network infrastructure much like users download and run virtual appliances on a virtual machine. To support the HyperNet abstraction, we created a Network Hypervisor service that provides a set of APIs that can be called to create a virtual network with certain characteristics. To evaluate the HyperNet architecture, we implemented several example Hyper-Nets and ran them on our prototype implementation of the Network Hypervisor. Our experiments show that the Hypervisor API can be used to compose almost any special-purpose network – networks capable of carrying out functions that the current Internet does not provide. Moreover, the design of our HyperNet architecture is highly extensible, enabling developers to write high-level libraries (using the Network Hypervisor APIs) to achieve complicated tasks.

Quadrature amplitude modulation (QAM) is a highly bandwidth efficient transmission technique for digital communications. It makes use of multiple signal phase and amplitude levels to carry multiple bits per symbol. This requires accurate and robust carrier phase and frequency estimation in the receiver. / Thesis (PhDElectronicEngineering)--University of South Australia, 2002.

This thesis examines the sampling and jitter specifications and considerations for Global Navigation Satellite Systems (GNSS) software receivers. Software Radio (SWR) technologies are being used in the implementation of communication receivers in general and GNSS receivers in particular. With the advent of new GPS signals, and a range of new Galileo and GLONASS signals soon becoming available, GNSS is an application where SWR and software-defined radio (SDR) are likely to have an impact. The sampling process is critical for SWR receivers where it occurs as close to the antenna as possible. One way to achieve this is by BandPass Sampling (BPS), which is an undersampling technique that exploits aliasing to perform downconversion. In this thesis, the allowable sampling frequencies are calculated and analyzed for the multiple frequency BPS software radio GNSS receivers. The SNR degradation due to jitter is calculated and the required jitter standard deviation allowable for wach GNSS band of interest is evaluated and a basic jitter budget is calculated that could assist in the design of multiple frequency SWR GNSS receivers. Analysis shows that psec-level jitter specifications are required in order to keep jitter noise well below the thermal noise for software radio satellite navigation receivers. However, analysis of a BPSK system shows that large errors occur if the jittered sample crosses a data bit boundary. However, the signal processing techniques required to process the BOC modulation are much more challenging than those for traditional BPSK. BOC and AltBOC have more transitions per chip of spreading code and hence jitter creates greater SNR degradation. This work derives expressions for noise due to jitter taking into account the transition probability in QPSK, BOC, AltBOC systems. Both simulations and analysis are used to give a better understanding of jitter effects on Software Radio GNSS receivers.

Bibliography: Last 9 leaves / 147, [61], 9 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1992

Quadrature amplitude modulation (QAM) is a highly bandwidth efficient transmission technique for digital communications. It makes use of multiple signal phase and amplitude levels to carry multiple bits per symbol. This requires accurate and robust carrier phase and frequency estimation in the receiver. / Thesis (PhDElectronicEngineering)--University of South Australia, 2002

Thesis (Ph.D.)--University of Wollongong, 2006. / Typescript. Includes bibliographical references: leaf 236-258.

Thesis (MIT(Informatics))-University of Pretoria, 2008. / Abstract in English. Includes bibliographical references.

Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 75-79). Also available in electronic format on the Internet.