Propagation Modeling and Characteristic Analysis of Terahertz Waves via High Altitude Platforms

Satellite-to-ground terahertz communication is limited by the power of signal source and antenna gain level,and has large path loss,which is difficult to implement.In this paper,a feasible scheme of satellite-to-ground terahertz communication using High Altitude Platforms(HAPs)as relay is presented,and the path loss on terahertz communication links is modeled and analyzed.Combined with the path loss model,the transmission loss along HAP-to-ground paths under different seasons and complex weather environment in Ali,Xizang,China is calculated.The results show that the transmission characteristics of terahertz waves in winter and summer are significantly different,mainly reflected in the number and bandwidth of usable atmospheric windows.Furthermore,the additional attenuation caused by the typical sand dust and ice cloud environment on terahertz band can reach 6.1 dB and 1.9 dB at the maximum respectively.With the aid of high gain antenna,the usable communication frequencies of the HAP-to-ground links in winter are significantly more than those in summer.When the transmitting and receiving antenna gain is 40 dBi respectively,the usable communication frequency can reach 1.35 THz in winter,while it is limited to less than 1 THz in summer,up to 0.493 THz.

COOPERATIVE DIRECTIONAL INTER-CELL HANDOVER SCHEME IN HIGH ALTITUDE PLATFORM COMMUNICATIONS SYSTEMS

A novel Cooperative Directional inter-cell Handover Scheme(CDHS) for High Altitude Platform(HAP) communications systems is proposed,in which the handover target cell and the two cells adjacent to this handover target cell work cooperatively to exploit the traffic fluctuation to improve handover performance.Users in the overlap area of the overloaded handover target cell will be forced to handover directionally before their optimal handover boundary in order to free up resources for the handover calls which would otherwise be dropped due to the shortage of resources and queue time out.Simulation results show that the handover call dropping probability is greatly reduced(at least 60%) compared with the general queue handover scheme,with little performance reduction to the call blocking probability,and the Not in the Best Cell(NBC) average time is only increased moderately.Moreover,an optimal cell radius can be achieved for a specific platform speed by minimizing the unified system performance,which is the linear combination of the handover call dropping probability and the NBC average time.

Statistical Modeling of the High Altitude Platform Dual-Polarized MIMO Propagation Channel

In order to investigate the benefit of multiple-input multiple-output(MIMO) technique applying to the high altitude platform(HAP), a 2×2 MIMO statistical model, which can accurately describe the channel between HAP and high-speed train, is presented. And dual polarization diversity is particularly considered. Based on first-order three-state Markov chain, the single-input single-output(SISO) channel, a subset of the MIMO channel is first established. The ray tracing approach applied to the digital relief model(DRM) which covers the railway between Xi'an and Zhengzhou is used to obtain the state probability vector and matrix of the state transition probability. The proposed model considers both Doppler shift and temporal correlation, and the polarization correlation and spatial correlation statistical properties of large-scale fading and smallscale fading are analyzed. Moreover, useful numerical results on the MIMO HAP channel outage capacity are provided based on which, significant capacity gains with respect to the conventional SISO case are illustrated. Such statistical channel model can be applied to the future wireless communication system between HAP and high-speed train.

STEERABLE ANTENNAS MOVEMENT COMPENSATION FOR HIGH ALTITUDE PLATFORM

High Altitude Platform(HAP) must compensate for relative motion with respect to the ground because of the stratosphere complexity,which is important to guarantee Quality of Service(QoS) in intended coverage area.With analysis on HAP movement models for predicting the geographical coverage in the cases of shift horizontally and vertically,yaw,roll and pitch,the mechanisms of steerable antennas movement compensation are investigated.The mechanism is applied to a scenario of 127 cell architecture,with a cell cluster size of four.By the simulation results of Carrier to Interference Ratio(CIR),the steerable antenna movement compensation mechanism decrease influence of HAP movement and guarantee effective coverage of the service area.

CAPACITY CALCULATION OF TD-CDMA HIGH ALTITUDE PLATFORM SYSTEM

A capacity calculation method of High Altitude Platform System(HAPS) is proposed in which TD-CDMA multiple access schemes are applied.With the influence of both power limit and bandwidth limit on capacity integrated,the paper derives the equations by which the capacity of TD-CDMA systems can be calculated,and performs calculation on a practical system.This calculation method is quite simple and effective with a comparatively small error,which is essential to the de-signing and research on HAPS.

A novel 3-D spatial temporal channel model for high mobility HAPS-based communications scenario

A high altitude platform station （HAPS） based communications scenario for providing Intemet access and broadband multimedia services to the passengers on board of a high speed train （traveling up to 300km/h） is proposed. Regarding the addressed scenario, when the propagation link between HAPS and train is blocked by obstacles, a three-dimensional （3-D） geometrical single cylinder spatial-temporal channel model is presented, in which closed form, mathematically tractable space-time correlation functions are obtained. It shows that the correlation functions determined by the 3-D model are of significant difference with those of the conventional 2-D model. Based on the analysis model, the paper derives a realized simulation model using sum-of-sinusoids approach, and applies method of equal areas （MEA） and modified method of equal areas （MMEA） to determine the model parameters. The fitting performance of the simulation model with the analysis one is evaluated by two means-square error （MSE） performance criteria. Finally, numerical simulation results verify the mathematical analysis conclusion, when N ≥21, simulation model has an excellent fitness with the analysis one.

高空平台不稳定性对HAPS通信性能影响建模与分析

由于高空平台不可能静止驻留在空中,平台打转、摇摆等状态就会对HAPS(High Altitude Platform Sta-tions)通信性能产生关键影响.目前的研究都处在假设平台稳定或调整波束指向能够补偿由于高空平台移动造成的剩余指向误差,存在很大的局限性,不能真实反应实际情况.本文通过建模把平台的不稳定性带来的影响反应到无线链路上,解决平台不稳定性等造成收发信号随机变化大而无法通信或通信质量差的问题.并通过仿真分析验证本文提出模型的正确性.

高空平台旋转对HAPS通信无线链路性能影响及抑制方法

近年来由高空平台构成的信息系统在通信领域的应用得到了广泛认同.高空平台站(High Altitude Platform Stations,HAPS)通信系统兼具卫星和陆地通信系统的优势,同时又有效避免了两者的缺点.高空平台不可能静止驻留在空中,平台的运动状态会对HAPS通信无线链路性能产生关键影响.目前的研究都集中考虑平台简单运动(水平或垂直移动)或假设平台稳定,这些研究存在很大的局限性.通过建立平台旋转状态特征参数体系,采取阵列天线设计、波束形成技术、小区覆盖与划分技术与平台状态相结合的方法,构建适合平台旋转状态下的无线链路模型,抑制平台旋转给HAPS通信链路性能带来的影响,解决高空平台旋转情况下HAPS通信无线链路存在误码、信号中断或传输信号盲区的问题,以保证无线链路性能,实现信号的可靠传输.

一种基于距离判决的HAPS通信无线DCA算法

本文提出一种基于距离判决的高空平台站(HAPS)通信的动态信道分配(DCA)算法,通过对无线链路功率到收发链路距离的转化,实时监测HAPS通信的收发链路距离来进行无线信道分配,解决HAPS通信中由于负载不均等造成的无线资源无法满足用户需求的问题.通过与随机信道分配算法及最差可接受信道分配算法的性能进行比较,本文提出的基于距离判决的算法能够在阻塞概率稍微增加的情况下解决系统连接中断问题,有效地提高了系统的整体性能.

HOT SPOT RELIEF WITH EMBEDDED BEAM FOR CDMA SYSTEMS IN HAPS

This paper proposes a novel micro/macro beam coverage scheme used in High Altitude Platform System (HAPS) Code Division Multiple Access (CDMA) systems. A relief of traffic burden in hot spot areas is achieved by embedding micro-beams into the macro-beams at the hot spot locations, together with appropriate power ratio control and user ratio control. The simulation results show that the hot spot problem can be relieved efficiently with the presented configuration, and a higher and more stable system capacity is expectable despite the variation of user distribution.

HAPS通信系统研究现状及展望

介绍了高空平流程电台(HAPS)通信系统国内外研究与频率划分的情况,根据WRC15相关决议分析我国在下个ITU研究周期关于HAPS的主要研究内容,并进行相应的影响分析与技术展望。

准静止状态下HAPS通信系统蜂窝小区覆盖特性分析

受到同温层环境的影响和位置保持技术的限制,高空平台(high altitude platform station,HAPS)不可能静止驻留在空中,而是容易发生偏移、打转、摇摆等,处于准静止状态。基于蜂窝小区模型,讨论高空平台水平偏移、垂直移动、旋转和摆动四种运动状态下多波束覆盖地面的几何特性,推导平台在任意状态下的地面接收机的接收功率表达式,并仿真分析平台不同状态下地面接收机接收功率变化,以期为小区切换判算法设计提供模型参考和依据。

Overview of development and regulatory aspects of high altitude platform system

High Altitude Platform(HAP)systems comprise airborne base stations deployed above 20 km and below 50 km to provide wireless access to devices in large areas.In this paper,two types of applications using HAP systems:one with HAP Station(HAPS)and the other with HAPS as International Mobile Telecommunication(IMT)Base Station(HIBS)are introduced.The HAP system with HAPS has already received wide recognition from the academia and the industry and is considered as an effective solution to provide internet access between fixed points in suburban and rural areas as well as emergencies.HAP systems with HIBS to serve IMT user terminal have just started to draw attention from researchers.The HIBS application is expected to be an anticipate mobile service application complementing the IMT requirement for cell phone or other mobile user terminals in which the service field of HAPS application cannot reach.After describing and characterizing the two types of systems,coexistence studies and simulation results using both the Power Fluxed Density(PFD)mask and separation distance based methods are presented in this paper.This paper also predicts future trends of the evolution paths for the HAP systems along with challenges and possible solutions from the standpoint of system architectures and spectrum regulation.

基于高空平台的边缘计算卸载:网络、算法和展望

高空平台(high altitude platform,HAP)技术与多接入边缘计算(multi-access edge computing,MEC)技术的结合将MEC服务器部署区域由地面扩展到空中,打破传统地面MEC网络的局限性,为用户提供无处不在的计算卸载服务。针对基于HAP的MEC卸载研究进行综述,首先,从HAP计算节点的优势、网络组成部分、网络结构、主要挑战及其应对技术4个方面分析基于HAP的MEC网络;其次,分别从图论、博弈论、机器学习、联邦学习等理论的角度对基于HAP的MEC卸载算法进行横向分析和纵向对比;最后,指出基于HAP的MEC卸载技术目前存在的问题,并对该技术的未来研究方向进行展望。

基于风力发电的高空浮空平台能源平衡研究

针对平流层浮空器驻空过程中出现的能源需求问题,提出了一种基于风力发电的高空浮空平台,根据驻空时的浮重平衡、推阻平衡为基础,设计了系统的高度联合调节机制,建立了系统在高度变化过程中的能源平衡模型。在此基础上,根据特定区域的风场数据,计算驻空过程中系统整体的能量产生及能量消耗,对系统的能源平衡性能进行分析计算。研究结果表明,在两个特定点的实际风场中,系统均能在驻空的同时,满足自身的能源需求,保证系统的能源平衡。

水电站溢洪道高架塔机拆除施工技术

为满足南屯1水电站溢洪道高架塔机拆除用400 t吊车的承载力和作业宽度,在大坝主体下游临空侧,创新采用叠梁门在相邻闸墩上浇筑混凝土墩搭设简支梁为下游侧吊车前支腿提供支撑;下游侧后支腿采用在溢洪道闸墩上浇筑混凝土墩作为支撑平台;上游侧前支腿和侧后支腿均采用在大坝主体顶面上铺设工字钢作为支撑平台;并利用理论和数值模拟方法,对支撑平台承载力的安全性进行验证,结果表明,支撑平台可满足400 t吊车在拆除高架塔机时的承载力和作业宽度,在总结拆除施工工艺流程和要点的基础上,成功利用废弃叠梁门拆除了南屯1水电站溢洪道高架塔机,取得了良好的经济效益,可为高空受限环境下塔机拆除施工提供有益借鉴。

基于平台摆动模型的平流层CDMA系统呼叫控制方案

本文分析了平流层平台摆动对HAPS-CDMA系统的影响,完善了平台不稳定性的研究,并提出摆动对小区内和对小区间干扰因子的概念,给出此时系统容量的计算方法;提出了一种用户呼叫控制方案,即:处于受平台摆动方向上的中心参考小区边缘用户的信号由相邻的两个基站同时接收的策略,来避免"乒乓切换",仿真结果说明该方案很好的平衡了系统容量和系统资源,对系统性能的改善明显.

平台水平移动对高空平台通信系统性能的影响

基于飞艇或飞行器的高空平台(HAP)通信系统面临的一个主要的挑战是平台位置保持。平台保持准静止位置的代价较大。因而,通常建议平台保持在一个位置圆柱内。本文推导终端采用固定指向天线时平台水平最大偏移距离计算公式,并分析有限和无限呼叫持续时间条件下覆盖区蜂窝内呼叫的切换概率。研究表明,平台最大水平偏移距离随着终端波束带宽的增大而增加;相同的波束带宽条件下,平台高度越低,要求的最大偏移距离越小。此外,当最大偏移距离较小时,平台的水平移动只在蜂窝边界附近区域产生切换,且越靠近边界呼叫切换概率越大。蜂窝内平均呼叫切换概率随着平台最大偏移距离的增加而增大;呼叫持续时间内平台移动距离越大,蜂窝内平均呼叫切换概率越大。当呼叫持续时间或平台速度趋于无穷大时,切换概率达到最大值。

低仰角动态环境下高空平台站通信信道的衰落特性

在分析高空平台站通信系统覆盖特性、链路损耗特性与降雨衰减特性的基础上,针对低仰角动态环境下的信道特性,根据传播散射理论,通过引入阴影系数,建立了一个包含好状态和坏状态的混合状态衰落统计模型.针对不同状态得到了模型高阶统计特性的表达式,并将模型的一阶和高阶统计特性通过实测数据进行验证,发现两者吻合良好.证明该模型可用于高空平台站通信电波传播特性的分析、调制及编码方案的优化和通信系统性能的仿真等.

从汶川地震通信问题谈平流层应急通信的应用

汶川地震暴露了我国应急通信系统不能满足突发事件通信需求,必须研究新型应急通信技术以克服当前应急通信存在的问题。提出了一种应用平流层通信技术实现应急通信系统的方法:在由飞艇组成的高空航空平台上装载基于微波技术的应急指挥通信系统和蜂窝移动基站,应急指挥通信系统用于突发事件的指挥通信,蜂窝移动通信用于公众通信。分析表明,平流层应急通信系统符合应急通信需求,具有部署快、成本低、容量大等特点。