Channel Measurement, Modeling, and Simulation for 6G: A Survey and Tutorial

The sixth generation (6G) mobile communications have attracted substantial attention in the global research community of information and communication technologies (ICT). 6G systems are expected to support not only extended 5G usage scenarios, but also new usage scenarios, such as integrated sensing and communication (ISAC), integrated artificial intelligence (AI) and communication, and communication and ubiquitous connectivity. To realize this goal, channel characteristics must be comprehensively studied and properly exploited, so as to promote the design, standardization, and optimization of 6G systems. In this paper, we first summarize the requirements and challenges in 6G channel research. Our focus is on channels for five promising technologies enabling 6G, including terahertz (THz), extreme MIMO (E-MIMO), ISAC, reconfigurable intelligent surface (RIS), and space-air-ground integrated network (SAGIN). Then, a survey of the progress of the 6G channel research regarding the above five promising technologies is presented in terms of the latest measurement campaigns, new characteristics, modeling methods, and research prospects. Moreover, a tutorial on the 6G channel simulations is presented. We introduce the BUPTCMG- 6G, a 6G link-level channel simulator, developed based on the ITU/3GPP 3D geometry-based stochastic model (GBSM) methodology. The simulator supports the channel simulation of the aforementioned 6G potential technologies. To facilitate the use of the simulator, the tutorial encompasses the design framework, user guidelines, and application examples. This paper offers in-depth, hands-on insights into the best practices of channel measurements, modeling, and simulations for the evaluation of 6G technologies, the development of 6G standards, and the implementation and optimization of 6G systems.Comment: 41 pages,52 figure

Multi-Objective Optimization of Laser Cleaning Quality of Q390 Steel Rust Layer Based on Response Surface Methodology and NSGA-II Algorithm

To improve the laser cleaning surface quality of rust layers in Q390 steel, a method of determining the optimal cleaning parameters is proposed that is based on response surface methodology and the second-generation non-dominated sorting genetic algorithm (NSGA-II). It involves constructing a mathematical model of the input variables (laser power, cleaning speed, scanning speed, and repetition frequency) and the objective values (surface oxygen content, rust layer removal rate, and surface roughness). The effects of the laser cleaning process parameters on the cleaning surface quality were analyzed in our study, and accordingly, NSGA-II was used to determine the optimal process parameters. The results indicate that the optimal process parameters are as follows: a laser power of 44.99 W, cleaning speed of 174.01 mm/min, scanning speed of 3852.03 mm/s, and repetition frequency of 116 kHz. With these parameters, the surface corrosion is effectively removed, revealing a distinct metal luster and meeting the standard for surface treatment before welding

Impact of climate factors on height growth of Pinus sylvestris var. mongolica.

Tree height growth is sensitive to climate change; therefore, incorporating climate factors into tree height prediction models can improve our understanding of this relationship and provide a scientific basis for plantation management under climate change conditions. Mongolian pine (Pinus sylvestris var. mongolica) is one of the most important afforestation species in Three-North Regions in China. Yet our knowledge on the relationship between height growth and climate for Mongolian pine is limited. Based on survey data for the dominant height of Mongolian pine and climate data from meteorological station, a mixed-effects Chapman-Richards model (including climate factors and random parameters) was used to study the effects of climate factors on the height growth of Mongolian pine in Zhanggutai sandy land, Northeast China. The results showed that precipitation had a delayed effect on the tree height growth. Generally, tree heights increased with increasing mean temperature in May and precipitation from October to April and decreased with increasing precipitation in the previous growing season. The model could effectively predict the dominant height growth of Mongolian pine under varying climate, which could help in further understanding the relationship between climate and height growth of Mongolian pine in semiarid areas of China

Parameterization of Mean Terminal Velocity of Hydrometeors in Convective Clouds

The relationships between mean terminal velocity and volume mean diameter of different hydrometeors, as well as how they change with different background aerosol concentrations have been investigated with numerical simulations of tropical deep convection from the Weather Forecast and Research Model (WRF), coupled with spectral bin microphysics. The results showed a positive correlation between either the mass-weighted mean terminal velocity (Vm) or the number-weighted mean terminal velocity (Vn) and the volume-mean diameter (Dv), with a correlation coefficient greater than 0.8. The number concentrations of both large and small hydrometeors increase with enhanced aerosol loading, resulting in increased Vm and decreased Vn. The parameterizations of Vm (Vn) were established under different aerosol conditions. The parameterized Vm (Vn) was then compared with default values used in the model when a fixed shape parameter (gamma distribution) was used in the bulk microphysics, which suggests smaller Vm and larger Vn values from the parameterizations. Moreover, the proposed parameterizations were further applied to the Morrison microphysical scheme for the simulation of a convective cloud. Changes in Vm and Vn as mentioned above directly affect the sedimentation of precipitating hydrometeors, such as raindrops, snow, and graupel, which lead to increased (decreased) mass (number) concentration of hydrometeors

Determining an Accurate and Cost-Effective Individual Height-Diameter Model for Mongolian Pine on Sandy Land

Height-diameter (H-D) models are important tools for forest management practice. Sandy Mongolian pine plantations (Pinus sylvestris var. mongolica) are a major component of the Three-North Afforestation Shelterbelt in Northern China. However, few H-D models are available for Mongolian pine plantations. In this paper we compared different equations found in the literature for predicting tree height, using diameter at breast height and additional stand-level predictor variables. We tested if the additional stand-level predictor variable is necessary to produce more accurate results. The dominant height was used as a stand-level predictor variable to describe the variation of the H-D relationship among plots. We found that the basic mixed-effects H-D model provided a similar predictive accuracy as the generalized mixed-effects H-D model. Moreover, it had the advantage of reducing the sampling effort. The basic mixed-effects H-D model calibration, in which the heights of the two thickest trees in the plot were included to calibrate the random effects, resulted in accurate and reliable individual tree height estimations. Thus, the basic mixed-effects H-D model with the above-described calibration design can be an accurate and cost-effective solution for estimating the heights of Mongolian pine trees in northern China

Formulating Strategy and Technology Path for Next-Generation Airworthiness Regulations of Aero-Engines

Airworthiness regulations are key for guaranteeing the safety of civil aviation products and a significant indication of a nation’s aviation power. A well-developed airworthiness regulation system is an effective technical and management means by which a country with an advanced aviation industry ensures the safety of its civil aviation products and occupies the broadest market share while using International Civil Aviation Organization (ICAO) rules. As major national science and technology projects for large aircraft, aero-engines, and gas turbines are implemented, it is imperative for China to further improve its airworthiness regulation system. In this study, we clarify the implications of aero-engine airworthiness regulations and summarize the problems regarding aero-engine airworthiness regulations both in China and abroad. Based on this, the formation strategy and technical path for the next-generation airworthiness regulations of aero-engines are explored from the perspectives of ICAO and China’s civil aviation industry. The formulation strategy emphasizes the requirement for system safety, and specific principles include an equivalent level of safety, clear logic, international compatibility, and local applicability. Moreover, a new top-level framework for the aero-engine airworthiness regulations is proposed; it inherits the international lessons learned, ensures a high safety standard, and adapts to the progress of system safety technologies of aero-engines. Furthermore, we suggest that China should continuously deepen the research, simultaneously expand application, and coordinate industry development, thus to promote the construction of the aero-engine airworthiness regulation system in China

Estimating surface fluxes over the north Tibetan Plateau area with ASTER imagery

Surface fluxes are important boundary conditions for climatological modeling and Asian monsoon system. The recent availability of high-resolution, multi-band imagery from the ASTER (Advanced Space-borne Thermal Emission and Reflection radiometer) sensor has enabled us to estimate surface fluxes to bridge the gap between local scale flux measurements using micrometeorological instruments and regional scale land-atmosphere exchanges of water and heat fluxes that are fundamental for the understanding of the water cycle in the Asian monsoon system. A parameterization method based on ASTER data and field observations has been proposed and tested for deriving surface albedo, surface temperature, Normalized Difference Vegetation Index (NDVI), Modified Soil Adjusted Vegetation Index (MSAVI), vegetation coverage, Leaf Area Index (LAI), net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous land surface in this paper. As a case study, the methodology was applied to the experimental area of the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau (CAMP/Tibet), located at the north Tibetan Plateau. The ASTER data of 24 July 2001, 29 November 2001 and 12 March 2002 was used in this paper for the case of summer, winter and spring. To validate the proposed methodology, the ground-measured surface variables (surface albedo and surface temperature) and land surface heat fluxes (net radiation flux, soil heat flux, sensible heat flux and latent heat flux) were compared to the ASTER derived values. The results show that the derived surface variables and land surface heat fluxes in three different months over the study area are in good accordance with the land surface status. Also, the estimated land surface variables and land surface heat fluxes are in good accordance with ground measurements, and all their absolute percentage difference (APD) is less than 10% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the ASTER data and filed observation over the study area

Xenotransplantation of human adipose-derived stem cells in zebrafish embryos.

Zebrafish is a widely used animal model with well-characterized background in developmental biology. The fate of human adipose-derived stem cells (ADSCs) after their xenotransplantation into the developing embryos of zebrafish is unknown. Therefore, human ADSCs were firstly isolated, and then transduced with lentiviral vector system carrying a green fluorescent protein (GFP) reporter gene, and followed by detection of their cell viability and the expression of cell surface antigens. These GFP-expressing human ADSCs were transplanted into the zebrafish embryos at 3.3-4.3 hour post-fertilization (hpf). Green fluorescent signal, the proliferation and differentiation of human ADSCs in recipient embryos were respectively examined using fluorescent microscopy and immunohistochemical staining. The results indicated that human ADSCs did not change their cell viability and the expression levels of cell surface antigens after GFP transduction. Microscopic examination demonstrated that green fluorescent signals of GFP expressed in the transplanted cells were observed in the embryos and larva fish at post-transplantation. The positive staining of Ki-67 revealed the survival and proliferation of human ADSCs in fish larvae after transplantation. The expression of CD105 was observable in the xenotransplanted ADSCs, but CD31 expression was undetectable. Therefore, our results indicate that human ADSCs xenotransplanted in the zebrafish embryos not only can survive and proliferate at across-species circumstance, but also seem to maintain their undifferentiation status in a short term. This xenograft model of zebrafish embryos may provide a promising and useful technical platform for the investigation of biology and physiology of stem cells in vivo

Modeling the land surface water and energy cycles of a mesoscale watershed in the central Tibetan Plateau during summer with a distributed hydrological model

The Tibetan Plateau (TP) is the highest plateau in the world, playing an essential role in Asian monsoon development and concurrent water and energy cycles. In this study, the Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) was calibrated and used to simulate water and energy cycles in a central TP watershed during the summer season. The model was first calibrated at a point scale (BJ site). The simulation results show that the model can successfully reproduce energy fluxes and soil surface temperature with acceptable accuracies. The model was further calibrated at basin scale, using observed discharges in summer 1998 and the entire year of 1999. The model successfully reproduced discharges near the basin outlet (Nash-Sutcliffe efficiency coefficients 0.60 and 0.62 in 1998 and 1999, respectively). Finally, the model was validated using MODIS land surface temperature (LST) data and measured soil water content (SWC) at 15 points within the watershed in 2010. The simulation results show that the model successfully reproduced the spatial pattern and LST means in both nighttime and daytime. Furthermore, the model can generally reproduce 15-site averaged SWC in four soil layers, with small bias error and root mean square error. Despite the absence of long-term discharge data for model verification, we validated it using MODIS LST and measured SWC data. This showed that the WEB-DHM has the potential for use in poorly gauged or ungauged areas such as the TP. This could improve understanding of water and energy cycles in these areas