Two–Way Relaying Communications with OFDM and BICM/BICM-ID

Relay-aided communication methods have gained strong interests in academic community and been applied in various wireless communication scenarios. Among different techniques in relay-aided communication system, two-way relaying communication (TWRC) achieves the highest spectral efficiency due to its bi-directional transmission capability. Nevertheless, different from the conventional point-to-point communication system, TWRC suffers from detection quality degradation caused by the multiple-access interference (MAI). In addition, because of the propagation characteristics of wireless channels, fading and multipath dispersion also contribute strongly to detection errors. Therefore, this thesis is mainly concerned with designing transmission and detection schemes to provide good detection quality of TWRC while taking into account the negative impacts of fading, multipath dispersion and multiple-access interference. First, a TWRC system operating over multipath fading channels is considered and orthogonal frequency-division multiplexing (OFDM) is adopted to handle the inter-symbol interference (ISI) caused by the multipath dispersion. In particular, adaptive physical-layer network coding (PNC) is employed to address the MAI issue. By analyzing the detection error probability, various adaptive PNC schemes are discussed for using with OFDM and the scheme achieving the best trade-off among performance, overhead and complexity is suggested. In the second part of the thesis, the design of distributed precoding in TWRC using OFDM under multipath fading channels is studied. The objective is to design a distributed precoding scheme which can alleviate MAI and achieve multipath diversity to combat fading. Specifically, three types of errors are introduced when analyzing the error probability in the multiple access (MA) phase. Through analysis and simulation, the scheme that performs precoding in both time and frequency domains is demonstrated to achieve the maximum diversity gains under all types of errors. Finally, the last part of the thesis examines a communication system incorporating forward error correction (FEC) codes. Specifically, bit-interleaved code modulation (BICM) without and with iterative decoding (BICM-ID) are investigated in a TWRC system. Distributed linear constellation precoding (DLCP) is applied to handle MAI and the design of DLCP in a TWRC system using BICM/BICM-ID is discussed. Taking into account the multiple access channel from the terminal nodes to the relay node, decoding based on the quaternary code representation is introduced. Several error probability bounds are derived to aid in the design of DLCP. Based on these bounds, optimal parameters of DLCP are obtained through analysis and computer search. It is also found that, by combining XORbased network coding with successful iterative decoding, the MAI is eliminated and thus DLCP is not required in a BICM-ID system

Global transpiration data from sap flow measurements : the SAPFLUXNET database

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.Peer reviewe

A Fault Diagnosis Scheme Using Hurst Exponent for Metal Particle Faults in GIL/GIS

A diagnosis scheme using the Hurst exponent for metal particle faults in GIL/GIS is proposed to improve the accuracy of classification and identification. First, the diagnosis source signal is the vibration signal generated by the collision of metal particles in the electric field. Then, the signal is processed via variational mode decomposition (VMD) based on particle swarm optimization with adaptive parameter adjustment (APA-PSO). In the end, fault types are classified and identified by an SVM model, whose feature vector is composed of the Hurst exponents of each intrinsic mode function (IMF-H). Extensive experimental data verify the effect of this new scheme. The results exhibit that the classification performance of SVM is significantly improved by the new feature vector. Furthermore, the VMD based on APA-PSO with adaptive parameter adjustment can effectively enhance the decomposition quality

Simulation with a structure-based mass-transfer model for turbulent fluidized beds

A structure-based mass-transfer model for turbulent fluidized beds (TFBs) was established according to mass conservation and the balance of mass transfer and reaction. Unlike the traditional method, which assumes a homogeneous structure, this model considered the presence of voids and particle clusters in TFBs and built correlations for each phase. The flow parameters were solved based on a previously proposed structure-based drag model. The catalytic combustion of methane at three temperatures and ozone decomposition at various gas velocities were used to validate the model. The TFB reactions comprised intrinsic reaction kinetics, internal diffusion, and external diffusion. The simulation results, which compared favorably with experimental data and were better than those based on the average method, demonstrated that methane was primarily consumed at the bottom of the bed and the methane concentration was closely related to the presence of the catalyst. The flow and diffusion had an important effect on the methane concentration. This model also predicted the outlet concentrations for ozone decomposition, which increased with increasing gas velocity. Interphase mass transfer was presented as the limiting step for this system. This structure-based mass-transfer model is important for the industrial application of TFBs. (C) 2017 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved

Simulation with a structure-based mass-transfer model for turbulent fluidized beds

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Simulation of mass transfer in downer fluidized beds with a structure-based consideration

The gas-solid mass transfer in the downer fluidized bed is analyzed theoretically in this work. Compared to the homogeneous assumption in each calculating grid, a structure-based model was proposed that the process was divided into the mass transfer in the cluster and dispersed phases. Simulations were performed with the cooperation of the Euler-Euler two-fluid method. The model predictions are in good agreement with the previous reported experimental measurements under a wide range of operating conditions. Simulated ozone profiles show a sharp conversion in the acceleration region, and a gentle conversion in the fully developed region. The transition point is well consistent with the boundary measured experimentally. These results show that the consideration of the heterogeneous structure results in a better understanding and prediction of mass transfer in downers. (C) 2019 Elsevier Ltd. All rights reserved

Preparation of Ta/W Composite by CVD

The Ta/W composites with 10%W, 13%W and 18%W were prepared by chemical vapor deposition (CVD). The properties of Ta/W composites were investigated by optical microscopy (OM), scanning electron microscopy (SEM ) and tensile test. The results show that it is possible to prepare Ta/W composites with different W volume fractions by CVD, and the actual densities of the composites are more than 99.4% of the theoretical density. Both Ta and W layers have columnar grain structures, and the more close to the interface, the more fine the grains are. The mechanical properties of CVD Ta/W are better than those of CVD Ta or CVD W. After hot treatment(1600 ℃×2 h),the diffused layers of the composites have become more wider and the mechanical properties are increased remarkably, and the tensile strength of the CVD Ta/W composite with 18%W is 660 MPa

Structure-based simulation of mass transfer in turbulent fluidized beds without local equilibrium assumption

Traditional methods based on local equilibrium assumption are unsuitable to describe the non-linear and non-equilibrium mass transfer in turbulent fluidized beds (TFBs), especially for industrial-scale reactors. In this work, the structure-based mass balance equations are proposed to describe the transfer and reac-tion of component on the surface of particles. These equations are valid and reasonable whether mass transfer and chemical reaction are in local equilibrium or not. Since local equilibrium assumption is not used, the proposed method can directly describe the transfer-reaction systems in TFBs, which are not in local equilibrium. Moreover, the proposed mass balance equations have also considered the meso-scale flow of particles. This can better reflect the transfer of component caused by the convection of particles in TFBs than the traditional models. The accuracy of the present model prediction was con-firmed by comparison of the predicted results and the experimentation being available in literatures.(c) 2022 Elsevier Ltd. All rights reserved