We investigate the issues in making a delay-based protocol adaptive to heterogeneous environments. We assess and address the problems a delay-based protocol faces when competing with a loss-based protocol such as TCP. We investigate if noise and variability in delay measurements in environments such as cable and ADSL access networks impact the delay-based protocol behavior significantly. We investigate these issues in the context of incremental deployment of a new delay-based protocol, PERT. We propose design modifications to PERT to compete with the TCP flavor SACK. We show through simulations and real network experiments that, with the proposed changes, PERT experiences lower drop rates than SACK and leads to lower overall drop rates with different mixes of PERT and SACK protocols. Delay-based protocols, being less aggressive, have problems in fully utilizing a highspeed link while operating alone. We show that a single PERT flow can fully utilize a high-speed, high-delay link. We performed several experiments with diverse parameters and simulated numerous scenarios using ns-2. The results from simulations indicate that PERT can adapt to heterogeneous networks and can operate well in an environment of heterogeneous protocols and other miscellaneous scenarios like wireless networks (in the presence of channel errors). We also show that proposed changes retain the desirable properties of PERT such as low loss rates and fairness when operating alone. To see how the protocol performs with the real-world traffic, the protocol has also been implemented in the Linux kernel and tested through experiments on live networks, by measuring the throughput and losses between nodes in our lab at TAMU and different machines at diverse location across the globe on the planet-lab. The results from simulations indicate that PERT can compete with TCP in diverse environments and provides benefits as it is incrementally deployed. Results from real-network experiments strengthen this claim as PERT shows similar behavior with the real-world traffic.

Based on the Lyapunov stability theorem, an adaptive sliding mode control scheme is proposed in this thesis for a class of systems with mismatched state-delayed perturbations to solve regulation problems. The main idea is that some adaptive mechanisms are embedded both in the sliding surfaces and in the controllers, so that not only the mismatched perturbations are suppressed during the sliding mode, but also the information of upper bound of perturbations is not required. The sliding surface functions are firstly designed through the usage of designed pseudo controllers, which is capable of stabilizing the reduced-order systems. The number of the sliding surface functions required by the proposed control scheme depends on the relationship between systems's dimension and number of inputs. The second step is to design the controllers so that the trajectories of the controlled system are able to reach sliding surface in a finite time. Once the controlled system enters the sliding mode, the asymptotical stability is guaranteed. Two numerical examples and one practical experiment are given for demonstrating the feasibility of the proposed control scheme.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

The studies of the designs on true-time-delay lines (TTDLs), n-bit digital phase shifters and wideband switched-line phase shifters using composite right/left-handed transmission-line (CRLH TL) unit cells are presented in this thesis. To simplify these designs, a symmetrical CRLH TL unit cell having equal input and output impedance is proposed. In the design of TDDLs, the symmetrical CRLH TL unit cell with higher time-delay efficiency helps achieve a size reduction of 67.9%, compared with the TTDL designed using right-handed transmission line (RH TL). The symmetrical CRLH TL unit cell is further modified to a compact CRLH TL unit cell to further reduce the size by 58%. For performances comparison, the TTDLs using the compact CRLH TL unit cells, symmetrical CRLH TL unit cells and RH TL are studied using computer simulation and measurement. Results show that the TTDLs using the compact CRLH TL unit cells can achieve much longer time delays. The TTDLs designed using CRLH TL unit cells have narrow bandwidths because CRLH TL unit cells have narrow bandwidths. In this thesis, a wideband unit cell obtained by rotating the CRLH TL unit cell by 900is proposed in the design of TTDLs. Simulation and measurement show that the TTDL using wideband unit cells can achieve a time delay about 3 times and 6 times longer than that of the periodic microstrip line (PML) and RH TL, respectively. A 2-bit, 3-bit and 6-bit phase shifters using symmetrical CRLH TL unit cells are designed using computer simulation. In these designs, positive-intrinsic-negative (PIN) diodes mounted on the fingers of the CRLH TL unit cells are used as switches to control the phase response at the output. Different phase shifts are achieved using different switching states determined by controlling bits. The phase shifters are fabricated and measured. Simulated and measured results agree very well. Power-handling capability is also analyzed using surface-current density on the CRLH TL unit cells. Results show that the phase shifters have much higher power-handling capabilities than that of the PIN diodes. A wideband 1800-switched-line phase shifter using symmetrical CRLH TL unit cell is proposed. The switched-line phase shifter employs a symmetrical CRLH TL unit cell as the reference arm and a RH TL as the delay arm to produce a constant phase shift across a wide frequency band. For comparison, a traditional 1800-switched-line phase shifter using RH TLs for both reference and delay arms is also designed. To reduce the size, the CRLH TL unit cell is realized using lump elements (LEs). Wideband 900-and 1800-switched-line phase shifters using LE-CRLH TL unit cells are studied and compared with the traditional 900-and 1800-switched-line phase shifters. Simulated and measured results show that the proposed designs using symmetrical CRLH TL unit cells and LE-CRLH TL unit cells have very constant phase shifts with smaller variations compared with the traditional designs. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

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ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / Radio transmission channel influences greatly the quality of transmitted voice and data signal in terms of data rate and robustness. This degradation is as a result of many factors, notable amongst them are having multiple replica of the transmitted signal at the receiver (multipath), changes of frequency as a result of the movement of the aircraft (Doppler shift) and noise. This paper characterizes the scattered components of the aeronautical channel in terms of delay spread. Geometric representation is used to derive expressions for the maximum delay spread using the 2-ray model and the three dimensional model of the scattered path. Furthermore, the delay and Doppler frequencies are described as a function of the horizontal distance to the specular reflection point between a ground station and a test article. The simulated results are compared to measured data of related articles and the value of the maximum delay spread is compared with the proposed intersymbol guard band for Orthogonal Frequency Division Multiplexing (OFDM) in the Integrated Network Enhanced Telemetry (iNET) program to see if this proposition can be adapted to the aeronautical channel.

Since Mobile network operator (MNO) relies on many Business Support Systems (BSS) and Operation Support Systems (OSS) it should be assured that operator’s systems supports the requirements of the future.This thesis shall focus on the “start-to-end” aspects that must be considered to ensure that International Roaming continues to operate flawless. The thesis experience Long Term Evolution (LTE) in case of international roaming by measuring the end to end location update delay.In order to evaluate the LTE performance of international roaming, the delay time has been measured by the means of tracing tools for several different international roamers and the results has been compared with the results achieved for local user. The outcome has been compared with the respecting results in 3G network the statistical results has been provided and the graphs has been plotted to study the performance.Based on the results obtain on this thesis, it has been concluded that local user acts more stable to get attach to the network, i.e. there are less fluctuation in delay times for local user. Also the delay time in 3G networks is more than the LTE networks, however 3G networks acts more stable and there are less fluctuation to get connects to 3G networks.

No description available.

Die vorliegende Dissertation befasst sich mit der seit Beginn der neunziger Jahre des 20. Jahrhunderts kontinuierlich gestiegenen Erwerbspartizipation von Studierenden während der Vorlesungszeit. Die Entwicklung dieses Verhaltens wurde vor dem Hintergrund der gesunkenen Bereitschaft zum Belohnungsaufschub theoretisch erklärt und empirisch untersucht. Dazu wurde eine Online-Befragung durchgeführt, an der sich 529 Studierende aus verschiedenen deutschen Städten beteiligten. Resultierend aus der statistischen Analyse der gewonnenen Daten zeigte sich, dass die Stärke der psychischen Belastungen, die durch einen Belohnungsaufschub entstehen, den Umfang der wöchentlich investierten Zeit in einen studentischen Erwerb beeinflussen. Weitere Effekte gingen bei der Erklärung der Bedingungen, die die Intensität eines studentischen Erwerbs befördern, von konsumtiven und hedonistischen Wertorientierungen der Studierenden aus. Darüber hinaus spielen vorstrukturierende, studienbezogene Maßnahmen in den Fachbereichen der Hochschulen, antizipierte berufsperspektivische Unwägbarkeiten auf dem Arbeitsmarkt sowie Bestrebungen der Studierenden hinsichtlich größerer finanzieller Unabhängigkeit eine Rolle bei der Ausübung von Nebenjobs.

There is minimal information available regarding test characteristics of the Rourke and the NDDS, two tools commonly used to screen for developmental delay. The objectives are to (a) generate preliminary descriptive data about the population and outcomes of interest, (b) determine test characteristics of the tools compared to the gold standard assessment, BSITD-III. Thirty-six month old children at high risk of developmental delay were recruited from the Perinatal Follow-up Program at the IWK Health Centre in Halifax, NS. The Rourke and NDDS results were obtained via parental report, the BSITD-III via clinical assessment. Results suggest that both tools may possess appropriate test characteristics to screen for developmental delay. Both perform more accurately when the criterion for delay is extended to two flagged areas of concern on the assessment tools. In conclusion, both tools appear to be sensitive to detecting developmental delay. Further investigation via a full scale study is warranted.