甚小孔径终端(VSAT)卫星网络拓扑结构及接入方式

本文主要叙述VSAT—卫星网络类型及接入方式。从网络拓扑结构出发分析星形和网状两种网络形式、特点及通信业务。由中心站和若干个VSAT站组成的星形网络有三种通信方式:单跳、双跳和单、双混合式。在中心站的控制下,VSAT站之间通信要通过中心站经卫星线路实现,不能直接进行通信,线路延时较大,且通信业务受限。网状拓扑网络没有中心站,VSAT站之间可直接进行双向通信,线路延时小,在业务范围上也有新的突破。 VSAT网络接入方式极其重要,它决定着VSAT的性能,业务量及线路延时。不同的接入方式将影响卫星的利用率,信道容量的稳定性,结构的简易性,网络造价及组网灵活性等。据以上衡量标准,分别对TDM/FDMA、SCPC/FDMA、TDMA、CDMA和DAMA方式进行了分析,可根据用户不同的业务需求,组合并用,满足各种VSAT站灵活组网需要。     

基于卫星通信传输构建灾地无线应急网方案探讨

以发生最坏灾难为假设,基于现有卫星通信网络,针对救灾应用场景,提出了快速构建灾地无线网的几种方案,以供参考。     

Selective reject ALOHA/FCFS: An advanced VSAT channel access protocol

This paper proposes and evaluates selective reject (SREJ) ALOHA/FCFS, a highly efficient, flexible and robust multiaccess protocol for very small aperture terminal (VSAT) applications. SREJ-ALOHA with locally synchronous FCFS retransmission scheduling is a ‘semi-compatible’ enhancement of asynchronous SREJ-ALOHA, which has earlier been shown to be an attractive satellite channel sharing protocol for low volume bursty terminals with variable length messages. The FCFS retransmission scheduling policy proposed here broadens the applicability of SREJ-ALOHA by providing higher maximum throughput, particularly in the important source traffic scenario with bimodal message length distributions. Improved channel-sharing efficiency and delay are achieved by exploiting time-of-arrival feedback naturally embedded in an unslotted SREJ-ALOHA channel to develop an implicit time-of-arrival based (FCFS) ordering for conflict-free, locally synchronous retransmission of most contending messages. An analytical procedure for evaluation of stability, throughput and delay for a general finite source, variable message length traffic model is described. The model is used to demonstrate that random access SREJ-ALOHA/FCFS typically achieves a maximum throughput in the region of 0·4–0·45 along with excellent stability and delay properties. In addition, a natural extension of the protocol which supports implicit reservation for long messages is described and shown to offer a high maximum throughput (>0·6), comparable to that achieved by highly co-ordinated slotted systems, for example mixed interactive/file-transfer traffic scenarios.     

基于弹性数据流卫星通信的农村电网调度自动化系统

VSAT卫星通信组网比较适合于农村电网的现状。适当改进信息传输方案,采用弹性数据流通信既可节省信息流量,又降低卫星通道的租用费用。通过卫星组建通信网络和改进自动化信息传输方案,可以建立一个既能节省初期投资又能节省运行费用的农村电网调度自动化系统。     

A probabilistic model to describe the interference produced by VSAT MF‐TDMA networks

This paper develops a mathematical model to describe the statistical behavior of the interference produced by VSAT/MF‐TDMA networks. The model is used to assess the interference produced by the uplinks of a VSAT/MF‐TDMA network into links of a network that uses a neighboring satellite. In the proposed model, analytical expressions were developed to account for the effects of variations in transmitting powers, antenna sizes, and transmitting antenna pointing errors. The earth station locations are modeled by a 2‐dimensional Poisson point process. The model is general enough to accommodate other types of point processes and can be applied to situations involving service areas containing multiple types of earth station geographical distribution. Numerical results obtained with the proposed model are compared with those based on the actual parameter values (eg, earth station locations, antenna sizes, and transmitting powers), which were provided by a Brazilian satellite operator.     

VSAT监视系统频率校正技术

分析了在通信系统中对通信危害较大的频率漂移问题的产生原因。着重阐述了在监视系统研制过程中针对频率漂移问题所提出的以外向信道为参考基准，通过周期性检测外向信道的频偏值，软件实时修正各用户信道接收频率的解决方法。     

双向卫星实时远程教学系统的研究与设计

介绍了一种基于双向卫星的多媒体远程实时教学系统AstroTrainer。通过教学现场的师生视音频数据、屏幕数据和白板数据的采集和基于双向卫星的网络传输。实现了教学现场的多媒体直播。克服了双向卫星回传带宽过窄的缺陷。提供了师生间的实时交互和课堂管理监控的功能。利用双向卫星高速接入技术，解决了传统课堂教学在时问和空间上的制约问题，大大扩展了教学规模，实现名师授课、教育资源的共享以及师生的协同交互。     

陕-京输气管道VSAT卫星通信系统

分析了陕－京输气管道的通信要求,简介了陕－京输气管道通信系统,着重介绍了ＶＳＡＴ卫星通信系统。根据作者参加投标的多种方案筛选和电测难证,到推荐选择Ｋｕ波段ＶＳＡＴ卫星通信方案,对运行的系统提出了卫星子网加盟和建立多主站ＶＳＡＴ卫星网的建议,通过多种应急通信手段发展的预测,对暂缓选用海事卫星Ａ型站给予了肯定。     

VSAT卫星通信技术在电力系统的应用

简要介绍ＶＳＡＴ卫星通信系统的特点,组网方式,在分析电力系统信息传输需求的基础上,在电力系统通信网络中,提出通过建立ＶＳＡＴ系统,可以解决一些边远地区的变电所及发供电单位在采用地面通信方式无法解决信息传输的问题,针对各种不同的信息传输需求,提出了不同的ＶＳＡＴ网络组网建设方案及建议。     

烟草卫星网VSAT数据通信系统的响应时间与优化分析

响应时间是卫星通信网络系统设计和应用的重要性能指标。在VSTA卫星通信网中,不同类型的业务应用对响应时间的要求也不同,响应时间主要由通信系统中的各个环节产生的时延构成。本文以烟草卫星通信网VSAT数据通信系统为例,从分析网络的时延入手,对系统响应时间进行了分析,提出提高烟草卫星网数据通信系统使用效率的方案。