3D non-stationary geometry-based stochastic model for unmanned aerial vehicle air-to-ground multi-input multi-output channels

A three-dimensional non-stationary geometry-based stochastic model for unmanned aerial vehicle(UAV)air-to-ground multi-input multi-output(MIMO)channels is proposed.The scatterers surrounding the UAV and ground station are assumed to be distributed on the surface of two cylinders in the proposed model.The impact of UAV rotations and accelerated motion is considered to describe channel non-stationarity.The computational methods of the corresponding time-variant parameters,such as UAV antenna array angles,time delays,and maximum Doppler frequencies,are theoretically deduced.The model is then used to derive channel statistical properties such as space-time correlation functions and Doppler power spectral density.Finally,numerical simulations are run to validate the channel s statistical properties.The simulation results show that increasing the UAV and ground station accelerations can reduce the time correlation function and increase channel non-stationarity in the time domain.Furthermore,the UAV s rotation significantly influences the spatial correlation function,with rolling having a greater influence than pitching.Similarly,the different directions of UAV movement significantly impact the Doppler power spectral density.

Channel Modeling for Air-to-Ground Wireless Communication

In this paper, we discuss several large-scale fading models for different enviromnents. The COST231-Hata model is adapted for air-to-ground modeling. We propose two criteria for air-to- ground channel modelling based on test data derived from field testing in Beijing. We develop a new propagation model that is more suitable for air-to-ground communication that previous models. We focus on improving this propagation model using the field test data.

俄乌冲突对军事目标属性判别能力发展的启示

快速、准确的军事目标属性判别是战争中需要首先解决的问题。在俄乌冲突中由于目标属性判别手段不完善、使用不规范,频频发生误伤事件,引发了国际上的极大关注。以俄乌冲突中的典型误伤事件为背景,分析了交战双方采用的无线电类、光学类目标属性判别手段以及误伤原因,提出军事目标属性判别能力形成所需的装备建设需求和使用关注要点,以期为军事目标属性判别能力发展建设提供启示。

理性颓退和销铄的挽歌——《我的菩提树》的一种解读

极“左”路线摧残下众多知识分子心理和灵魂颓退销铄经历了如下过程：首先，知识分子在“思想改造”和自虐阶段，已经丧失了独立的品格，丧失了人的尊严，粉碎了原有的智慧；其二，随着无休止的运动和批斗，使他们在出卖自己的同时，开始了对别人的出卖，在“文革”中形成了空前的自我厮杀，造成了民族心理的大变态；其三，知识分子在心灵粉碎堕落的同时，又面临着肉体也被毁灭的危险。经济贫穷，盛行封建迷信没有法制可言，劳改农场干部素质低下，是造成上述情形的主要原因。

空地误伤避免技术特点分析及其发展趋势研究

自二战以来,多次战争记录近距空中支援误伤己方地面部队的案例。随着战争中介入大量的媒体报道,美军开展研究、开发和应用一系列敌我识别技术,以期望在联合作战中减少误伤,对未来技术应用发展有极大的参考和学习价值。

Physical Layer Security for UAV Communications:A Comprehensive Survey

Due to its high mobility and flexible deployment,unmanned aerial vehicle(UAV)is drawing unprecedented interest in both military and civil applications to enable agile and ubiquitous connectivity.Mainly operating in an open environment,UAV communications benefit from dominant line-of-sight links;however,this on the other hand renders the communications more vulnerable to malicious attacks.Recently,physical layer security(PLS)has been introduced to UAV systems as an important complement to the conventional cryptography-based approaches.In this paper,a comprehensive survey on the current achievements of UAV-PLS is conducted.We first introduce the basic concepts including typical static/-mobile UAV deployment scenarios,the unique air-toground channel and aerial nodes distribution models,as well as various roles that a UAV may act when PLS is concerned.Then,we start by reviewing the secrecy performance analysis and enhancing techniques for statically deployed UAV systems,and extend the discussion to the more general scenario where the UAVs’mobility is further exploited.For both cases,respectively,we summarize the commonly adopted methodologies,then describe important works in the litera ture in detail.Finally,potential research directions and challenges are discussed to provide an outlook for future works in the area of UAV-PLS.

理性颓退和销铄的挽歌——《我的菩提树》的一种解读

在极“左”路线摧残下,众多知识分子的灵魂颓退销铄经历了:在“思想改造”和自虐阶段,丧失了独立的品格和人的尊严,粉碎了原有的智慧;随着无休止的运动和批斗,他们开始出卖自己与别人的同时,在“文革”中进行了空前的自我厮杀,造成了民族心理的大变态;知识分子在心灵粉碎堕落的同时,又面临着肉体毁灭的危险。

Fixed-time adaptive model reference sliding mode control for an air-to-ground missile

This paper addresses the fixed-time adaptive model reference sliding mode control for an air-to-ground missile associated with large speed ranges, mismatched disturbances and un-modeled dynamics. Firstly, a sliding mode surface is developed by the tracking error of the state equation and the model reference state equation with respect to the air-to-ground missile. More specifically,a novel fixed-time adaptive reaching law is presented. Subsequently, the mismatched disturbances and the un-modeled dynamics are treated as the model errors of the state equation. These model errors are estimated by means of a fixed-time disturbance observer, and they are also utilized to compensate the proposed controller. Therefore, the fixed-time controller is obtained by an adaptive reaching law and a fixed-time disturbance observer. Closed-loop stability of the proposed controller is established. Finally, simulation results including Monte Carlo simulations, nonlinear six-DegreeOf-Freedom(6-DOF) simulations and different ranges are presented to demonstrate the efficacy of the proposed control scheme.

Machine learning based altitude-dependent empirical LoS probability model for air-to-ground communications

Line-of-sight(LoS)probability prediction is critical to the performance optimization of wireless communication systems.However,it is challenging to predict the LoS probability of air-to-ground(A2G)communication scenarios,because the altitude of unmanned aerial vehicles(UAVs)or other aircraft varies from dozens of meters to several kilometers.This paper presents an altitude-dependent empirical LoS probability model for A2G scenarios.Before estimating the model parameters,we design a K-nearest neighbor(KNN)based strategy to classify LoS and non-LoS(NLoS)paths.Then,a two-layer back propagation neural network(BPNN)based parameter estimation method is developed to build the relationship between every model parameter and the UAV altitude.Simulation results show that the results obtained using our proposed model has good consistency with the ray tracing(RT)data,the measurement data,and the results obtained using the standard models.Our model can also provide wider applicable altitudes than other LoS probability models,and thus can be applied to different altitudes under various A2G scenarios.

斯坦贝克弑兄故事与圣经隐喻

在人类的伦理禁忌中,兄弟背叛与弑杀是一种比乱伦更古老、更厉害的伦理罪行,它的社会表现形式就是国家和种族内部的战争。斯坦贝克在其一生的文学创作中,始终关注人类历史中永恒存在的兄弟背叛与弑杀行为。他认为,人类几千年的兄弟背叛与弑杀,根源于人类伦理本性中的二元性对立:即个体性与群体性、自我之爱与自我之恨、善良与邪恶。根除兄弟背叛与弑杀的终极途径不是暴力手段,而是理性的伦理选择,那就是理性意志与和解。