厘米级扩频测距系统自校准链路分析

针对未来遥感、导航等卫星对地面测控设备的距离测量精度由米级提高到厘米级这一问题,简要介绍了航天测控常用的距离零值标校方案,并量化分析了天线和模拟信道设备引入的距离零值变化,认为必须引入与工作链路同时工作的距离零值自校准链路。针对扩频测距系统对自校准链路的信号形式进行了讨论,并对工作信号电平与自校准链路信号电平之间的相互影响进行了理论分析及仿真,认为自校准链路信号电平低于工作信号电平10 d B是一个较优的选择。     

卫星移动通信系统的监测效果仿真分析

文章以ITU-R报告M.2398中的静止轨道卫星移动通信系统的参数为例,研究卫星移动通信系统的监测效果。对于下行链路,仿真计算表明监测效果良好;对于上行链路,仿真计算表明,地基监测系统对上行链路进行监测的覆盖范围约为2.5～5 km,基于21 km高度的高空平台（HAPS）的监测系统对上行链路进行监测的覆盖范围在最小通信仰角取5°时约为203 km。     

无线传感器网络链路通信质量测量研究

首先分析了传统链路测量方法所存在的问题,提出了均值RSSI(接收信号强度显示)、均值LQI(链路质量显示)测量法,通过测量及计算RSSI、LQI的均值,可以较为准确地获得链路通信质量信息;其次构建了发送功率改变、硬件校准改变、周围环境改变和并发干扰等实验案例,分析了均值RSSI、均值LQI在上述案例下的测量性能,定义了链路测量灵敏度,计算了均值RSSI、均值LQI的灵敏度值,对RSSI及LQI用于链路通信质量测量和性能评估做出了全面的权衡。     

一种非对称链路带宽测量算法

准确的网络带宽测量对许多互联网应用和协议至关重要.现有带宽测量工具如Pathchar,Bing和Bprobe都假定链路对称.但ADSL、cable modem和卫星链路等的广泛存在,使测量必须考虑非对称链路.本文提出了一种新的非对称链路测量算法(ALBMA,Asymmetric Link Bandwidth Measurement Algorithm),来测量一条路径上各链路的双向带宽,并采用核密度评估算法过滤测量噪声.仿真验证了测量和滤波算法的有效性.与先前算法相比,ALBMA具有相近的测量精度,但测量速度更快,并且耗费网络资源少.     

卫星监测系统中链路的设计及使用效能的评估分析

卫星监测系统在接收信号的同时不可避免地会接收到噪声,噪声决定了系统的监测灵敏度。本文从噪声的角度研究了卫星监测系统中链路的设计对噪声系数的影响,分析了影响监测系统中监测灵敏度的因素,通过实际测量的数据对结果进行了评估验证。     

一种基于高聚集链路测量的网络级别OD流异常检测框架

绝大多数网络异常事件会对网络中的一定空间范围造成影响,形成分布式流量异常,其异常流量模式通常体现在网络级别源到端(OD)流的某些特征参数上.OD流很难直接测量得到,需通过高聚集链路测量反演技术推测,然而反演误差将直接影响下一步基于特征参数的异常诊断.本文提出了一种直接由链路测量进行OD流异常检测的框架,该框架采用RMLP神经网络,并加入部分OD流估计值作为约束输入,实现了由链路测量对OD流级别特征参数的估计.该方法的优点是检测过程不再完全依赖链路到OD流的估计,解决了反演误差影响检测的问题,并且该框架允许链路流量到多种OD流特征参数的估计.     

无线电设备射频参数测量中链路校准的不确定度评估

文章对无线电射频参数测量中链路校准因素的不确定度评估进行了研究,以WCDMA手机功率测量为例,对ETSITR100028-1标准给出的链路校准因素的不确定度评估方法做了分析和实验,指出了其缺陷,并提出了新的合理的评估方法。     

载噪比直接法测量卫星转发器G/T值的精度研究

阐述利用载噪比直接法测量卫星转发器天线品质因数G/T值的原理,对测试链路进行建模分析,研究大气损耗、天线方向跟踪误差给测量精度带来的影响。最后给出利用载噪比直接法测量卫星转发器G/T值的实例,与卫星转发器的出厂测试值进行对比,结果表明二者吻合度较高。     

卫星光通信光束对准误差分析

卫星间光通信链路中对准误差对接收功率和误码率都有严重的影响.对高斯型光束的传输与接收损耗的关系进行了研究,得出了接收光功率和误码率公式,并用数值分析方法进行了定量分析.     

某型舰载雷达方位数据传递链路误差分析

介绍了某型舰载雷达采用的同轴方位数据传递链路，对该方位数据传递链路进行了误差分析，并通过静态测试给出了链路的误差曲线，同时介绍了一种动态下可用来监测链路工作情况的方法，为分机调试、整机调试提供了方便。     

基于自适应丢包区分的卫星信道TCP改进

通过卫星扩展TCP/IP网络无论在商业还是军事上具有十分重要的意义。但由于链路的高时延、高误码率和严重的信道衰落,使得TCP/IP应用于卫星链路时,相对于有线链路性能较差,因此将TCP/IP应用于卫星链路时,必须对TCP/IP进行改进。提出了自适应特定队列管理的方法,其基本思想是根据网络事件动态调整模式匹配参数,使得在拥塞和卫星链路误码率增加的情况下,都具有较高的丢包区分准确率。     

Dynamic link analysis and its in‐orbit verification on a spin‐stabilized satellite mission Eu:CROPIS

In this paper, we present the in‐orbit verification of a dynamic link budget approach for the communication link of the Eu:CROPIS (Euglena and Combined Regenerative Organic‐Food Production in Space) satellite. Because of the high satellite spin rates of up to 30 rpm, the satellite antennas radio frequency beam becomes strongly dynamic, consisting of fast amplitude variations and phase rotations. Both effects degrade the link quality and might lead to an abort of the communication. The paper presents an accurate method of how to simulate these dynamic effects and examines the simulation outputs with real in‐orbit measurements. Both results are compared with each other, and deviations are discussed.     

车载非静止轨道卫星监测系统链路计算

非静止轨道(NGSO)卫星通信发展迅猛,但由于相关设备的缺乏,对其下行信号频率轨道资源占用情况监测较少,因此,设计NGSO监测系统为当前急需解决的问题。设计车载监测系统要求具有低的余量,而当前卫星监测系统通信链路计算过程考虑不够精确,文章通过研究ITU相关建议书,考虑NGSO通信链路中存在的大气、雨水、云层和电离层闪烁等相关因素,计算在特定接收余量下的车载监测系统地空链路损耗,为该系统设计提供更精确的依据,同时对GSO链路设计也具有参考意义。     

微小卫星通信关键技术浅析及其发展思路初探

微小卫星通信以数据存储转发为基础、以微小卫星组网为核心、以软件无线电技术为桥梁得以发展和应用。文中首先简要介绍了微小卫星通信中的数据存储转发、微小卫星组网、星上处理、星际链路以及软件无线电等几项关键技术,然后对微小卫星通信发展思路进行了初步探索,并提出了具体发展模式。     

Effects of solar transit on Ku-band VSAT systems

A satellite earth-station is affected by added radio noise from the Sun when the Sun passes behind the satellite as seen from the earth-station. In the following, an exact analysis of this solar transit is derived, and an approximate method is presented for practical cases. Moreover, networks of very small aperture satellite terminals (VSATs) operating at K_u-band microwave frequencies of 12–14 GHz behave differently during the solar transit period than the more traditional C- or K_u-band satellite networks; therefore analytical and experimental results for VSATs have been presented. An explanation is given, based on these analyses, of why solar transit outages are rarer in VSATs than in conventional satellite communications systems.     

ROBUST DATA LINK PROTOCOLS FOR CONNECTION-LESS SERVICE OVER SATELLITE LINKS

The performance of the connection-less network service (CLNS) over a satellite link with features such as high propagation delay and a varying (often high) level of errors, can be improved using the connection oriented data link (CODL) service. However, although existing CODL protocols satisfy the requirements of a connection oriented network protocol (e.g. X.25), they are not optimal for the CLNS over satellite links. The interaction of link error recovery procedures with the error recovery procedures implemented by CLNS users, the unnecessary delay due to link protocol sequencing and recovery procedures, and the interaction between applications with different quality of service (QoS) requirements cause most CODL protocols to have a detrimental impact on the performance of the CLNS. This study presents a new link protocol, which improves the quality of the CLNS (e.g. IP), especially considering the enhancement of the performance of connection-oriented transport protocols (e.g. TCP). The performance improvement using the new link protocols is demonstrated by implementation in a satellite interworking unit.     

地空数据链链路负载百分比及轮询方式下算法

地空数据链指挥控制系统要向飞机发送大量的指令和态势数据,而无线信道的传输速率有限,这就会有积攒未发出去的指令和态势由于超时而失效的问题.因此有必要引入一个表示数据链路负载状况和繁忙状况的量,使指控系统实时地了解链路的负载情况,采取相应措施.引入链路负载百分比来表示链路的负载和繁忙状况,以所发送的指令和态势不超时为标准,给出了链路负载的算法.     

Ku频段卫星通信链路设计

本文举例说明在一个Ku频段卫星通信链路中 ,卫星增益、EIRP、载波 /噪声比等之间的关系 ,并对Ku频段卫星通信链路的参数选择进行分析。     

Optimizing the End-to-End Performance of Reliable Flows over Wireless Links

Pure end-to-end error recovery fails as a general solution to optimize throughput when wireless links form parts of the end-to-end path. It can lead to decreased end-to-end throughput, an unfair load on best-effort networks, and a waste of valuable radio resources. Link layer error recovery over wireless links is essential for reliable flows to avoid these problems. We demonstrate this through an analysis of a large set of block erasure traces measured in different real-world radio environments, with both stationary and mobile hosts. Our analysis is based on a case study of the circuit-switched data service implemented in GSM. We show that the throughput on this wireless channel can be increased by using a larger (fixed) frame size for the reliable link layer protocol. This yields an improvement of up to 25% when the channel quality is good and 18% even under poor radio conditions. Our results suggest that adaptive frame length control could further increase the channel throughput. Finally, we discuss link and transport layer error control mechanisms and their interactions with end-to-end congestion control schemes. For reliable flows, we argue in favor of highly persistent error recovery and lossless handover schemes implemented at the link layer.     

Link adaptation and SINR errors in practical multicast multibeam satellite systems with linear precoding

The application of linear precoding at the gateway side enables broadband multibeam satellite systems to use more aggressive frequency reuse patterns increasing the overall capacity of future high-throughput satellites (HTS). In any practical precoded system, receivers can estimate only a few coefficients of the channel state information (CSI), while the others, in what is known as nullification, are set to zero. In this paper, the impact of the CSI nullification to the SINR estimation is analyzed statistically and geographically for a multicast multibeam satellite system. The errors in the SINR calculated by the gateway affect to the modulation and coding schemes (MCSs) selection, increasing the rate of erroneous frames or leading to an underutilization of the available resources. Therefore, as countermeasure, a link adaptation algorithm based on an adaptive margin per user is proposed, helping to achieve the error rate constraints of DVB-S2X systems without compromising the throughput, even under severe CSI degradation due to nullification and Rician fading.