"星链"卫星系统及国内卫星互联网星座发展思考

近年来国内外低轨互联网卫星星座得到了飞速发展,并取得了一定进展.针对我国卫星互联网发展中面临的问题,结合"星链"卫星系统的最新发展进行了仿真分析,并据此指出发展互联网卫星系统的重大意义,最后,提出一种适合我国发展的多轨道混合的卫星互联网方案.仿真结果表明,该方案可作为我国卫星互联网研发建设的一种思路.     

极轨卫星遥感图像数据传输系统的在轨测试和计算方法

阐述极轨卫星在轨运行期间，遥感图像数据传输系统的在轨测试和计算方法，给出测试数据，并对数据效果进行比较分析。     

面向低轨巨型星座的多目标卫星接入优化

低轨巨型星座可以提供全球无缝覆盖的卫星通信服务,但也会导致用户被卫星多重覆盖,如何选择最优的卫星进行接入,成为低轨巨型星座接入技术的关键问题。对此,提出一种基于粒子群的多目标卫星接入优化算法。综合考虑星地距离、卫星剩余可服务时间和卫星剩余负载等目标函数,根据不同业务类型的QoS需求,对参数赋予相应的权值;针对可视卫星数量多且动态变化的特点,通过粒子群算法进行低复杂度求解。仿真表明,相较于对比算法,所提算法对星地距离和卫星剩余可服务时间进行了优化折中,保障了服务时间和通信质量,提高了接入成功率,能够灵活满足用户的不同业务类型需求,适应用户业务不同时空分布以及业务离散化的场景。     

一种间隔重访的低轨星座设计方法

在低轨电子侦察、遥感卫星领域,针对非连续覆盖条件下的星座优化设计问题,提出了一种间隔重访的低轨星座设计方法。通过改进极轨覆盖带设计方法,将对地覆盖区域等效为矩形;以对地目标的平均重访间隔时间为输入,从同轨卫星间和相邻轨道面间两方面分析,得到近似最优的星座参数。通过STK仿真验证,设计的星座可满足重访间隔时间要求。     

一种面向低轨遥感星座的路由任务规划算法研究

为了解决遥感星座数据传输时效性差的问题,利用星间链组网,提出了一种适应于断续猝发特征星间网络的路由任务规划算法。该算法以遥感卫星成像任务规划结果为驱动,结合卫星网络拓扑结构的时变性特点,改进基于快照序列的拓扑划分方法,降低路由切换频率,减少链路切换代价损失。并将卫星与地面站之间的路由看作低轨遥感星座路由的一部分,在选择星地最短路由路径的同时实现星地建链总时长最大化。仿真结果表明,该算法能够显著提升低轨遥感卫星星座的数据传输能力。     

面向低轨卫星互联网的随机接入前导码传输技术

围绕低轨卫星随机接入过程中前导码传输性能开展研究,在对现有基于Zadoff-Chu(ZC)序列的两种前导码设计方案基础上,提出一个三级ZC根序列级联的前导码设计方法,并给出了复杂度分析结果。此外,在考虑离散傅里叶变换扩展正交频分复用(Discrete Fourier Transform spread OFDM,DFT-s-OFDM)波形传输的情况下,对低轨卫星随机接入过程前导码检测性能开展了系统级仿真。通过仿真首先探明了不同类型前导码进行峰值检测时所具有的最优检测阈值,其次探究了不同多普勒频移和多用户干扰对前导码检测性能的作用机理,最后分析了不同天气条件对多用户前导码检测性能的影响。上述研究显示采用多个ZC根序列级联的方法可显著提高低轨卫星随机接入用户的数量,但复杂度较高,且受多用户干扰和多普勒频移的影响,该方法的检测性能受限。     

卫星互联网星间激光通信链路传输与路由交换技术研究（特邀）

随着低轨卫星互联网的迅猛发展,星间激光通信链路成为低轨大型星座互联互通的关键,也是用户接入卫星互联网实现全球范围内端到端交互的基础。与地球同步轨道的星间环网不同,由于低轨卫星的高动态性,造成星间链路需要不断动态重构,由此带来空间节点的编址方式、交换路由方法等诸多技术难题,是目前该领域关注的热点。此外,用户终端通过微波链路接入卫星互联网,需要微波链路与激光链路之间的汇集和分发,也是迫切需要研究解决的重点难点问题。     

我国首颗低轨移动通信卫星完成在轨试验主要指标优于国际现有同类卫星

近日,由“清华大学-信威通信空天信息网络技术联合研究中心”研制的灵巧通信试验卫星已完成全部在轨测试试验,工程任务取得圆满成功,实现了我国首颗低轨移动通信卫星的重要突破。灵巧通信试验卫星于2014年9月4日在我国酒泉卫星发射中心成功搭载发射后,清华大学与信威通信联合团队开展了大量的卫星在轨测试试验,现已成功实现手持卫星终端通话、手持卫星终端与手机通话、互联网数据传输、电磁频谱监测定位及移动互联网业务,完成了灵巧通信试验卫星的工程任务,主要指标优于国际上现有的低轨移动通信在轨卫星的最好水平。     

我国首颗低轨移动通信卫星完成在轨试验主要指标优于国际现有同类卫星主要指标优于国际现有同类卫星

正近日,由"清华大学-信威通信空天信息网络技术联合研究中心"研制的灵巧通信试验卫星已完成全部在轨测试试验,工程任务取得圆满成功,实现了我国首颗低轨移动通信卫星的重要突破。灵巧通信试验卫星于2014年9月4日在我国酒泉卫星发射中心成功搭载发射后,清华大学与信威通信联合团队开展了大量     

Design and implementation of a wireless internet remote access platform

Recently, mobile networks and internet technologies have been widely developed for the voice communication and information retrieval services all over the world. Compared with the wire‐line internet environment, mobile networks have lower bandwidth, longer transmission latency and unreliable connection, and the capability of mobile terminals is restricted by the limited memory size, lower CPU computation capability and inconvenient I/O interface. These limitations restrict the development of the wireless internet applications. In this paper, we design and implement a ‘wireless internet remote access platform’ (WIRAP). The WIRAP platform interconnects the wireless network and internet to provide mobile users a remote centralized storage and computation environment. A mobile user can store large volume of data and execute complex computations on WIRAP instead of on the mobile terminals. WIRAP supports different network interfaces (e.g. short message service (SMS), wireless markup language (WML) and hyper text markup language (HTML) and users may use terminals (with different network capabilities) to access WIRAP. Copyright © 2006 John Wiley & Sons, Ltd.     

Interference from 24-GHz automotive radars to passive microwave earth remote sensing satellites

The automotive industry is currently considering the introduction of short-range radars (SRR) operating near 24 GHz for improving road traffic safety. SSRs are intended to observe the full azimuthal space cover around a vehicle using up to eight sensors. The sensors would operate in an ultrawideband (UWB) mode, occupying 3-5 GHz of bandwidth. Interference from SRR transmitters with passive microwave remote sensing satellites used for weather and climate monitoring could occur as the result of several coupling mechanisms, including direct coupling via the transmit antenna beam and scattering and diffraction of the transmitted signals from leading vehicles, buildings, and other nearby objects. In this study, we estimate the amount of coupling anticipated to occur from SRRs, including the direct and scattered contributions. The calculations are based on bistatic scattering measurements of a typical automobile and ray optical simulations of reflection and propagation in an urban environment. Using these calculations, the maximum allowable SRR transmitted power for interference levels acceptable for meteorological and climatological remote sensing applications are quantified. The study provides criteria for SRR operation with the Earth Exploration Satellite Service on a noninterference basis.     

低轨卫星通信遥感融合:架构、技术与试验

低轨卫星系统是获取空间信息和破解宽带数字鸿沟的重要基础设施之一,通信与遥感融合是解决现有遥感和通信分治、卫星重置、应急业务响应不及时等问题的有效途径。概述了低轨通信和遥感卫星系统的现状,针对通信和遥感融合需求,提出了通信遥感融合方案及体系架构,阐述了基于该体系架构的硬件组成及融合试验方案,最后探讨了相关挑战和未来发展。     

基于随机森林和纹理特征的苹果园遥感提取

为准确、快速地从高分影像中获取苹果种植分布信息,以QuickBird遥感影像为数据源,首先采用分形理论和灰度共生矩阵(GLCM)提取纹理特征,然后将提取的分形纹理和GLCM纹理特征分别与光谱特征组合,最后开展随机森林分类实验,对不同分类特征和不同分类方法的实验结果进行比较。结果表明:光谱+GLCM纹理识别苹果园的效果明显优于光谱特征和光谱+分形纹理,其苹果园提取精度为95.99%,比光谱分类显著提高11.83%,比光谱+分形纹理提高1.34%;在相同分类特征下随机森林分类结果最高,其中,随机森林结合光谱+GLCM纹理分类精度最高,总体精度和Kappa系数分别为95.30%和0.94,较最小距离和支持向量机分类有明显提高。     

基于集群和GPU的高光谱遥感影像并行处理

以高光谱遥感影像数据处理中的主成分分析（PCA）和最小噪声分离（MNF）以及光谱相关系数填图（SCM）算法的并行化为目标,分别在集群环境下基于MPI设计并实现了协方差矩阵并行算法,以及基于GPU设计并实现了SCM并行算法,并在高光谱遥感影像数据处理中得到应用和验证。实验结果表明,高光谱遥感影像数据处理高性能计算对于提高和改善其时间性能具有显著效果,是高光谱遥感工程化应用快速处理重要的技术手段。     

Multipacket reception in random access wireless networks: fromsignal processing to optimal medium access control

There has been considerable interest in the idea of cross-layer design of wireless networks. This is motivated by the need to provide a greater level of adaptivity to variations of wireless channels. This article examines one aspect of the interaction between the physical and medium access control layers. In particular, we consider the impact of signal processing techniques that enable multipacket reception on the throughput and design of random access protocols     

Reply to comments on "Interference from 24-GHz automotive radars to passive microwave Earth remote sensing satellites"

We appreciate that authors Kerr et al. concur that our paper [ibid., vol.42, no.7, p.1387-98 (2004)] provides the right approach to the analysis of potential interference from anthropogenic sources to remote sensing satellites. The potential for such interference is likely to grow as new active systems are developed, necessitating acceptable procedures for interference analysis based on accepted scientific knowledge and engineering principles. While some simple clarifications are in order to improve the acceptability of our procedure, we suggest, however, that Kerr et al. have not studied our paper in detail and misinterpret several points.     

Research on high-speed TDICCD remote sensing camera video signal processing

Video signal processing needs high signal-to-noise ratio (SNR) in high-speed time delay and integration charge coupled devices (TDICCD). To solve this problem, this article first analyzes the characteristics of the output video signal of a new type of high-speed TDICCD and its operation principle. Then it studies the correlation double sample (CDS) method of reducing noise. Following that a synthesized processing method is proposed, including correlation double sample, programmable gain control, line calibration and digital offset control, etc. Among the methods, XRD98L59 is a video signal processor for the charge coupled device (CCD). Application of this processor to one kind of high-speed TDICCD with eight output ports achieves perfect video images. The experiment result indicates that the SNR of the images reaches about 50 riB. The video signal processing for high-speed multi-channel TDICCD is implemented, which meets the required project index.     

基于遥感数据挖掘的智能地理信息系统设计

为了有效实现地理信息一体化管理,设计并实现一种基于遥感数据挖掘的智能地理信息系统。通过数据管理模块对空间数据库中的不同类型的地理数据进行管理和调度,在需要时可对地理信息数据进行可视化处理,同时融入真实场景中;利用三维处理模块对简单的三维图形进行描绘,代替实际地理环境中的地物,将其与真实场景融合;通过场景控制模块对虚拟物体和真实场景进行配准,基于当前现场场景判断所需从数据库提取的信息和显示的内容;依据网络传输模块链接系统的服务端和客户端,实现通信。软件设计过程中,对基于遥感数据挖掘的智能地理信息系统进行了详细地分析,并给出遥感数据挖掘的实现过程以及系统部分程序代码。实验结果表明,所设计的系统具有很高的实用性和可靠性。