Interference suppression and parameter estimation in wireless communication systems over time-varing multipath fading channels

This dissertation focuses on providing solutions to two of the most important problems in wireless communication systems design, namely, 1) the interference suppression, and 2) the channel parameter estimation in wireless communication systems over time-varying multipath fading channels. We first study the interference suppression problem in various communication systems under a unified multirate transmultiplexer model. A state-space approach that achieves the optimal realizable equalization (suppression of inter-symbol interference) is proposed, where the Kalman filter is applied to obtain the minimum mean squared error estimate of the transmitted symbols. The properties of the optimal realizable equalizer are analyzed. Its relations with the conventional equalization methods are studied. We show that, although in general a Kalman filter has an infinite impulse response, the Kalman filter based decision-feedback equalizer (Kalman DFE) is a finite length filter. We also propose a novel successive interference cancellation (SIC) scheme to suppress the inter-channel interference encountered in multi-input multi-output systems. Based on spatial filtering theory, the SIC scheme is again converted to a Kalman filtering problem. Combining the Kalman DFE and the SIC scheme in series, the resultant two-stage receiver achieves optimal realizable interference suppression. Our results are the most general ever obtained, and can be applied to any linear channels that have a state-space realization, including time-invariant, time-varying, finite impulse response, and infinite impulse response channels. The second half of the dissertation devotes to the parameter estimation and tracking of single-input single-output time-varying multipath channels. We propose a novel method that can blindly estimate the channel second order statistics (SOS). We establish the channel SOS identifiability condition and propose novel precoder structures that guarantee the blind estimation of the channel SOS and achieve diversities. The estimated channel SOS can then be fit into a low order autoregressive (AR) model characterizing the time evolution of the channel impulse response. Based on this AR model, a new approach to time-varying multipath channel tracking is proposed

Effects of Severe Water Stress on Maize Growth Processes in the Field

In this study, we investigated the effects of water stress on the growth and yield of summer maize (Zea mays L.) over four phenological stages: Seedling, jointing, heading, and grain-filling. Water stress treatments were applied during each of these four stages in a water-controlled field in the Guanzhong Plain, China between 2013 and 2016. We found that severe water stress during the seedling stage had a greater effect on the growth and development of maize than stress applied during the other three stages. Water stress led to lower leaf area index (LAI) and biomass owing to reduced intercepted photosynthetically active radiation (IPAR) and radiation-use efficiency (RUE). These effects extended to the reproductive stage and eventually reduced the unit kernel weight and yield. In addition, the chlorophyll content in the leaf remained lower, even though irrigation was applied partially or fully after the seedling stage. Severe and prolonged water stress in maize plants during the seedling stage may damage the structure of the photosynthetic membrane, resulting in lower chlorophyll content, and therefore RUE, than those in the plants that did not experience water stress at the seedling stage. Maize plants with such damage did not show a meaningful recovery even when irrigation levels during the rest of the growth period were the same as those applied to the plants not subjected to water stress. The results of our field experiments suggest that an unrecoverable yield loss could occur if summer maize were exposed to severe and extended water stress events during the seedling stage

Multiple-access interference suppression in CDMA wireless systems

This thesis presents techniques that suppress the multiple access interference (MAI) in CDMA wireless systems. MAI is the main factor that influences the communication quality and the capacity in CDMA wireless systems. Hence the suppression of MAI is essential to the performance of a CDMA wireless system. For conventional CDMA systems where matched filters are used as receivers, the only MAI suppression method available is the power control, which allocates each user in the system an appropriate transmitter power level such that the transmitter power is minimized to decrease the MAI, while at the same time each user maintains a given SIR requirement. Another MAI suppression method that has received much attention is the multiuser detection, which employs more complex receivers than the matched filters and uses signal processing techniques to suppress the MAI. These two methods form the basis for MAI suppression in CDMA wireless systems. In this thesis, we first investigate the power control method. A decentralized adaptive power control algorithm which requires only the received signal and the signature sequence of the desired user is discussed. Then the multiuser detection method is discussed. A blind adaptive multiuser detection algorithm that requires the same knowledge as matched filters to demodulate received signals is presented. Both theoretic study and simulation results show the effectiveness of these algorithms. Finally, power control and multiuser detection are combined together within the same system model. A power controlled multiuser detection algorithm is proposed, which preserves the decentralized property and is shown to be effective in simulation studies. Simulation results also show that this algorithm is superior to conventional power control algorithm and multiuser detection algorithm in terms of total transmitter power and more relaxed requirement on the SIR targets of the system

A Visualization Investigation on the Influence of the Operating Conditions on the Phase Change in the Primary Convergent-divergent Nozzle of a Transcritical CO2 Ejector

Complex flow processes exist in the primary convergent-divergent nozzle of a transcritical CO2 ejector because of the rapid expansion of the supercritical CO2 flow, which have a significant influence on the performance of a transcritical CO2 ejector expansion refrigeration system. A visualization experiment with the direct photography method was carried out to investigate the phase change phenomena in the primary convergent-divergent nozzle of a transcritical CO2 ejector. The visualization transcritical CO2 ejector was designed as a rectangular cross section to minimize the optical distortion. In order to better interpret the phase change phenomena of CO2 flow, four pressure measurement points were lumped in the convergent-divergent nozzle to get the pressure distribution along the convergent-divergent nozzle for various operating conditions. The results revealed that the phase change position in the convergent-divergent nozzle was closely related to the primary flow inlet conditions and the suction flow inlet pressure. .The results showed that the phase change could start after or before the nozzle throat, and the phase change position moved upstream by decreasing the primary flow inlet pressure and temperature simultaneously. As keeping the primary flow inlet pressure constant, the phase change position also moved upward by decreasing the suction flow inlet pressure. In addition, the measured pressure results indicated that the pressure differences in the convergent section of the primary convergent-divergent nozzle increased as the CO2 suction flow inlet pressure decreased because of more adequate expansion of the primary flow

Visual Investigation on Effect of Structural Parameters and Operation Condition of Two-phase Ejector

As an important component in transcritical CO2 refrigeration cycle, complex flow in ejector have not been clearly elucidated. In this paper, CO2 flow in two-phase rectangle ejector was investigated experimentally by visualization measurement. The phase transition and the relaxation phenomena in the ejector were observed. By analyze the picture and the data collected from this experiment, we study the relationship between efficiency of ejector and the phase transition position in the ejector. Firstly, the microstructure of the flow pattern in the ejector was captured by a high speed digital video camera with a microscope to analyze the mixing process in mixing chamber. It was found that there were two stages with different characteristics in mixing process ,which were named fluid mixing section and fluid equilibrium section. When fluid get through mixing channel, the ejector realize the majority functions of entrainment in the first stage, and the ejector also homogenize the velocity of primary fluid and secondary flow by the way of flow core expand to almost all the channel in the second stage. Secondly, based on the comparison of pictures collected from different ejectors under different operating conditions, we found that phase transition position and the form of phase transition was mainly depended on the entrance condition of motive nozzle. For an ejector that keeps the suction nozzle under the same operation condition, when the phase transition point trend to exit of motive nozzle, in mixing channel ,motive flow will occupy more space meanwhile the relaxation phenomena occurred in longer region. It was worth mentioning that the phase transition point will change with different operation condition. But there exist only one best position where the ejector contributes to best efficiency. So, it is of great significance to treat phase transition point as an important sign which was easy to be recognized. Visualization research of ejector will be an important reference for theoretical study of flow pattern in the ejector. It also can provide some date to validate the results from the numerical calculation. The visualization study of ejector will also be the basis of further learn of shock waves and delayed phase transition in the ejector

5-(2,3,4,5,6-Penta­fluoro­phen­yl)-1,3,4-thia­diazol-2-amine

The title compound, C8H2F5N3S, was synthesized by the reaction of perfluoro­benzoic acid and thio­semicarbazide. The dihedral angle between the thia­diazole and perfluoro­phenyl ring is 35.41 (6)°. In the crystal, inter­molecular N—H⋯N hydrogen bonds link the mol­ecules, forming a three-dimensional network

RePaint-NeRF: NeRF Editting via Semantic Masks and Diffusion Models

The emergence of Neural Radiance Fields (NeRF) has promoted the development of synthesized high-fidelity views of the intricate real world. However, it is still a very demanding task to repaint the content in NeRF. In this paper, we propose a novel framework that can take RGB images as input and alter the 3D content in neural scenes. Our work leverages existing diffusion models to guide changes in the designated 3D content. Specifically, we semantically select the target object and a pre-trained diffusion model will guide the NeRF model to generate new 3D objects, which can improve the editability, diversity, and application range of NeRF. Experiment results show that our algorithm is effective for editing 3D objects in NeRF under different text prompts, including editing appearance, shape, and more. We validate our method on both real-world datasets and synthetic-world datasets for these editing tasks. Please visit https://repaintnerf.github.io for a better view of our results.Comment: IJCAI 2023 Accepted (Main Track

Pharmacokinetics of ligustrazine ethosome patch in rats and anti-myocardial ischemia and anti-ischemic reperfusion injury effect

The objective of this study was to investigate the pharmacokinetics of the ligustrazine ethosome patch and antimyocardial ischemia and anti-ischemic reperfusion injury effect. Male Sprague Dawley rats were divided randomly into 3 groups: Group A (intragastric ligustrazine), Group B (transdermal ligustrazine ethosome patch), and Group C (conventional transdermal ligustrazine patch). After treatment, samples of blood and of various tissues such as heart, liver, spleen, lung, kidney, brain, and muscle samples were taken at different time points. Drug concentration was measured with HPLC, and the drug concentration–time curve was plotted. Pharmacokinetic software 3p97 was applied to calculate pharmacokinetic parameters and the area under the drug concentration–time curve (AUC) in various tissues. The rat model of acute myocardial ischemia was constructed with intravenous injection of pituitrin and the model of myocardial ischemia-perfusion injury was constructed by tying off the left anterior descending coronary artery of rats to observe the effect of ligustrazine ethosome patches on ischemic myocardium and ischemia-reperfusion injury. Results showed that AUC was highest in the transdermal drug delivery group of ligustrazine ethosome patch. There were significant differences in whole blood viscosity, plasma viscosity, hematocrit, red blood cell aggregation index, and deformation index between ligustrazine the ethosome patch group and ischemic control group (P < 0.01). Moreover, ligustrazine ethosome patches could reduce the scope of myocardial infarction induced by long-term ischemia. Ligustrazine ethosome patches have a sustained-release property. They can maintain stable and sustained blood drug concentration, increase bioavailability, and reduce administration times. The drug patch can decrease hemorheological indices of myocardial ischemia in rats, as well as protect acute ischemic myocardium and ischemia-reperfusion injured myocardium

Bayesian estimation of human impedance and motion intention for human-robot collaboration

This article proposes a Bayesian method to acquire the estimation of human impedance and motion intention in a human-robot collaborative task. Combining with the prior knowledge of human stiffness, estimated stiffness obeying Gaussian distribution is obtained by Bayesian estimation, and human motion intention can be also estimated. An adaptive impedance control strategy is employed to track a target impedance model and neural networks are used to compensate for uncertainties in robotic dynamics. Comparative simulation results are carried out to verify the effectiveness of estimation method and emphasize the advantages of the proposed control strategy. The experiment, performed on Baxter robot platform, illustrates a good system performance