OFDM-based WLAN systems are originally used for nearly static environment. But in the trend of user-convenience, if we want to support mobility, the most important issue is the Doppler effect caused by the object velocity. We investigate how the Doppler effect, signal-to-noise ratio (SNR) and imperfect estimation of channel impulse response (CIR) and the maximum Doppler shift fd influence the final bit error rate (BER) under the simulation environment, modified WLAN 802.11a specification. For these effects, we give some simulation results and conclusions. If CIR and df are known with the same number of multipath, we can see some phenomenon. First, the BER is dominated by AWGN noise. Second, under the same channel delay spread, the higher the object velocity is, the more serious the BER is. Third, under the same the object velocity, the more serious the BER is. If CIR is known instead of fd, under the same error percentage of fd and the same number of multipath, the lesser the velocity is the lesser the BER curve changes. If fd is known instead of CIR with the same number of multipath, the longer the channel delay spread is, the more serious the BER is.

No description available.

Thesis (doctoral)--Universität St. Gallen, 2002.

Thesis (Ph. D.)--University of Queensland, 2001. / Includes bibliographical references.

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.

Shigella is a causative agent of bacillary dysentery in humans. The ability of Shigella to disseminate in the intestinal epithelium is crucial for disease establishment. This process of cell-to-cell spread involves actin-based motility, which allows movement of Shigella through the cytoplasm, and the ability of Shigella to form filopodia-like membrane protrusions that are engulfed by adjacent cells. Compared to the process of Shigella actin tail assembly, which requires recruitment and activation of host actin modulators such as N-WASP and Arp2/3, the mechanism of how Shigella moves from an infected cell into neighboring cells and what host factors are involved remain poorly characterized. In this dissertation, I investigate whether members of the Ena/VASP family, as key actin regulators, or Inverse-BAR (I-BAR) family proteins, as coordinators of membrane curvature and actin dynamics, are required in dissemination of S. flexneri in a cell monolayer. Ena/VASP family proteins regulate cell migration, adhesion, shape, and cell-cell interaction. The members of the family include Vasodilator-Stimulated Phosphoprotein (VASP), Ena-VASP-like (Evl), and Mammalian enabled (Mena). We have previously shown that Mena, despite its localization to the actin tail, has no role in S. flexneri actin-based motility. Here, I investigate the role of Mena, Evl, and VASP in S. flexneri dissemination. I determine that the presence of VASP or Evl restricts cell-to-cell spread of S. flexneri. I further show evidence that the conserved EVH1 domain and phosphorylation of VASP regulate the ability of Shigella to spread. I-BAR proteins, including IRSp53 and IRTKS, contain a conserved domain that directly binds to membrane lipids and induces convex membrane deformation. This unique property and the ability of these proteins to bind F-actin and actin modulators are necessary for the formation of actin pedestals by pathogenic E. coli and filopodia. Using cells with reduced levels of IRTKS or IRSp53, I examine the role of these proteins in cell-to-cell spread and show that neither IRTKS nor IRSp53 is required for S. flexneri spread. Collectively, these results advance our understanding of host proteins that participate in S. flexneri dissemination.

This thesis is concerned with the experimental determination of the fundamental flame characteristics in a dust-air mixture and the influence of turbulence on flame propagation. Experiments were carried out in a tube having a 0.19 meter inside diameter and a length of 0.93 meter, and 1.86 meter with both ends closed. A dispersion system was developed giving a good quality uniform dust suspension. A comparative method for the estimation of dust flame characteristics, based on well defined methane-air flame characteristics, was developed and employed to estimate the characteristics of a flame propagating in a cornstarch dust-air mixture. A systematic study of the influence of dispersion-induced turbulence on the dust flame propagation was carried out. The influence of obstacles on flame propagation also was investigated. Some mechanisms of flame propagation in a cornstarch dust-air mixture have been proposed and discussed. In the conclusion, general remarks concerning the dust flame characteristics and the influence of turbulence on flame propagation are made. The future direction of research is also indicated.

No description available.

No description available.

This thesis consists of two parts: the first examines the Expectations Hypothesis of the Term Structure for New Zealand, and the latter examines the predictive power of the term spread on future economic activity in New Zealand. For both parts, I divide the sample period into two sub-sample periods – the pre-OCR period and the OCR period. Using Mankiw & Miron’s (1986) approach for testing the expectations hypothesis, the findings in this paper suggest that the theory is consistent with New Zealand data during the OCR period. I attribute the success of the theory to the introduction of the Official Cash Rate system in March 1999. The change from targeting the settlement cash balance to targeting an interest rate variable has substantially improved the predictability of short-term interest rates. In regards to the predictive power of the spread, the findings in this paper support the conventional view that the spread is positively related to future economic activity. Using Hamilton & Kim’s (2002) approach, I decomposed the term spread into an expectation component and a term premium in an attempt to find out whether these two variables have distinctly separate effect on future economic activity. My findings are in contrast to that reported by Hamilton & Kim. In particular, I find that the term premium in some cases is significant and negatively related to future economic activity in New Zealand. I attribute the negative relationship to lower long-term interest rates and a fallen term premium in New Zealand.