卫星移动通信系统集群通信竞争回退策略研究

在卫星移动通信系统基础上,实现集群通信组呼功能。当前卫星组呼通信采用固定频率方式,组呼成员在一个频率下进行通信,实用性差。针对组呼用户身份转换竞争上行信道的过程,为降低用户碰撞概率,提出一种针对媒体接入控制层(Medium Access Control,MAC)的一键通(Push To Talk,PTT)竞争回退策略,并仿真给出了各优先级的用户的概率曲线。仿真结果表明,竞争策略能够很好地保证优先级高的用户有较大的PTT竞争成功的概率。     

临时、应急通信中卫星通信应用及运行操作中的几个关注点

在临时或应急卫星通信应用中,较多地采用了车载卫星站或便携式卫星站的方式在现场建立通信传输链路。在现场,通过一辆(台)或数辆(台)卫星车或便携式卫星站,将现场各类图像、数据、话音、指挥调度或移动基站的信号传送到远端,建立卫星双向(或单向)链路,以实现现场信息传送、指挥调度建立或现场通信保障等。非固定地球站在卫星通信传输的运行操作中的必须关注站址的选择、通信系统的性能掌控、卫星资源(频率)申请、上星的许可,并做好非固定地球站在运行中的卫星通信链路质量管控,确保本站和相应卫星的通信运行质量。     

GEO卫星LTE跨层资源调度算法

地球同步轨道(GEO)卫星通信系统具有通信时延长的特点,适用于GEO卫星长期演进(LTE)通信的资源调度算法非常重要。为提升星上资源分配的高效性,基于可变最大加权时延优先(M-LWDF)算法,提出了一种综合考虑媒体接入控制(MAC)层参数和应用层参数的跨层调度算法。该算法在MAC层从数学角度推导,提出权重更大的时延判决因子及在应用层根据业务优先级不同引入Q因子。仿真结果表明,与M-LWDF算法相比,不同业务情况下,跨层资源调度算法减小了通信时延,提高了系统吞吐量,但公平性能略有下降并增加了复杂度。     

中国卫通坚定守卫特殊领域,以独特手段保障通信安全

自2002年提出转型以来,中国卫通以保障国家卫星通信广播安全、服务国民经济和社会发展为已任,确立了以卫星广播通信、指挥调度通信、应急通信、调度指挥通信和卫星导航定位通信等特殊领域的通信及农村通信、海上通信等特殊区域的通信为主导,以小容量、广覆盖、机动化的网络结构为支撑,专注发展特色业务、提供特色服务的企业发展思路,并以此发展思路为指导,加快业务创新步伐,加大结构调整力度,强化市场开拓,大力培育新经济增长点,坚定不移地走有卫星通信广播特色的发展之路,形成了卫星通信广播电视、数字集群应急通信和卫星导航定位综合信息…     

卫星集群组呼业务通知过程

集群通信在指挥调度及抢险救灾中发挥中重要作用，目前地面集群通信网络的覆盖范围有限，在处理有些紧急事件时可能会超出网络覆盖。依托通信对距离不敏感的卫星移动通信，在GMR-1标准基础上实现组呼呼叫业务功能，可以扩大集群通信的覆盖面积。对空闲模式下组呼通知过程进行了研究，对处于空闲模式下的移动台使用简化的NCH监听机制做了概述，最后提出了组呼通知信道的配置方法，计算得到NCH信道可以支持的话务量，与现有的GSM网络通信的相比具有更高的寻呼效率、可以承栽更大的用户数量。     

综合信息

数码视讯助力国家某部数码视讯为国家某部搭建的卫星视频通信系统于近日完成调试验收并顺利交付。数码视讯自主研发的"星捷"卫星视频通信系统,实现了总中心、分中心、卫星通信车的三级指挥调度,能够针对卫星通信信道进行智能视频优化处理,匹配各种卫星通信信道状态,最大化地利用现有卫星资     

天地一体化应急信息网及多址方式研究

卫星通信作为传统地面通信在空间的拓展和补充,有许多地面通信手段无法比拟的优点,文中首先介绍了卫星通信在应急通信系统中的应用,针对目前通信体制多样、互联互通较困难、一些部门的应急通信系统不支持图像、视频等宽带多媒体业务的现状,提出了实现地基通信网和天基信息网的有效联动、构建天地一体化应急信息网的设想,并分析了在卫星的频率和功率资源受限的条件下宽带多媒体卫星和移动卫星的多址接入方式的选择。     

卫星集群IP多播组呼业务协议研究

现有集群通信覆盖范围有限,为实现全方位集群通信,提出将卫星通信与集群通信相结合。以TETRA为例,分析了现有国内外集群通信系统集群业务的实现方式。针对电路域集群,提出实现分组域多媒体集群。为更利于工程实现,提出了基于MBMS技术的卫星集群IP多播组呼业务协议流程,并分析了实现中需要解决的关键问题及解决方案。该方案将为卫星移动通信集群业务的发展提供新的方向。     

FAS双中心在沈局客专通信系统的应用

MDS3400调度指挥通信系统是新一代统一指挥调度通信平台,它集语音、数据业务应用为一体。该系统有着强大调度指挥功能,通过2B+D连接各种智能调度台、指挥台,支持调度指挥所需的各种功能,如选呼、组呼、通播、强拆、强制、分群等调度功能,支持多用户多级别设置;支持IP分布式网络部署,具有开放性、兼容性、高可靠性的特点,拥有灵活的综合接入方式及先进的维护手段。     

TETRA移动台下行链路突发到逻辑信道映射的实现

集群通信系统是多个用户或部门群体共用一组无线电信道,并动态地使用这些信道的专用移动通信系统,主要用于指挥调度通信。文章首先简要介绍了TETRA系统中移动台（MS）侧MAC层基本工作原理,然后详细阐述了移动台接收下行突发到逻辑信道映射方案的实现。     

卫星集群应急通信系统

卫星通信以其独特的特点,在许多场合中具有重要的应用价值。在指挥调度、应急救灾等场合中一般使用地面集群通信,但是其信号覆盖范围有限,集群通信组网受频率资源限制比较大。将具有覆盖面积大、受地理条件限制小以及通信频带宽等特点的卫星通信系统与地面集群通信系统结合组网,形成天地一体化的通信网络。     

Radio resource management across multiple protocol layers in satellite networks: a tutorial overview

Satellite transmissions have an important role in telephone communications, television broadcasting, computer communications, maritime navigation, and military command and control. Moreover, in many situations they may be the only possible communication set‐up. Trends in telecommunications indicate that four major growth market/service areas are messaging and navigation services (wireless and satellite), mobility services (wireless and satellite), video delivery services (cable and satellite), and interactive multimedia services (fibre/cable, satellite). When using geostationary satellites (GEO), the long propagation delay may have great impact, given the end‐to‐end delay user's requirements of relevant applications; moreover, atmospheric conditions may seriously affect data transmission. Since satellite bandwidth is a relatively scarce resource compared to the terrestrial one (e.g. in optical transport networks), and the environment is harsher, resource management of the radio segment plays an important role in the system's efficiency and economy. The radio resource management (RMM) entity is responsible for the utilization of the air interface resources, and covers power control, handover, admission control, congestion control, bandwidth allocation, and packet scheduling. RRM functions are crucial for the best possible utilization of the capacity. RRM functions can be implemented in different ways, thus having an impact on the overall system efficiency. This tutorial aims to provide an overview of satellite transmission aspects at various OSI layers, with emphasis on the MAC layer; some cross‐layer solutions for bandwidth allocation are also indicated. Far from being an exhaustive survey (mainly due to the extensive nature of the subject), it offers the readers an extensive bibliography, which could be used for further research on specific aspects. Copyright © 2005 John Wiley & Sons, Ltd.     

Satellite antennas

Communication satellites have evolved from a radio relay in space to encompass other applications such as processing and meteorology. The demand for high capacity communication satellites has led in the past two decades to the development of multibeam antennas, a landmark in satellite antenna technology. Satellite antennas are classified into three categories according to function: communication; tracking, telemetry, and command (TT and C); and special satellite antennas. While the application of shaped beam antennas has been developed to its fullest extent as in INTELSAT VI and VII, an active monolithic microwave integrated circuit (MMIC) phased array will play an important role in future satellite antenna technology. Examples of each state-of-the-art satellite antenna technology and the process of space qualification are presented briefly     

Channel Capacity Statistics of an Interfered Broadband Satellite Link

Satellite communication networks play an important role in the “digital divide” problem, by offering broadband services everywhere in the world. The ever increasing demand for multimedia services has led to the use of Ku, Ka and V band in modern satellite communication networks. In these frequency bands, rain attenuation is the most dominant propagation fading mechanism. Moreover, interference due to propagation phenomena deteriorates the performance of the satellite links and should be taken into account for the reliable design of satellite communication networks. In this paper, an analytical physical mathematical propagation model is presented for the prediction of channel capacity statistics of a dual-polarized interfered broadband satellite link. Rain attenuation spatial inhomogeneity is incorporated in the analysis with the employment of correlated slant paths. The obtained numerical results show the significance of these effects to channel capacity estimation. Finally, the proposed model may be used towards the optimum utilization of the satellite channel capacity by means of adaptive fade mitigation schemes.     

Using traffic prediction and estimation of provider revenue for a joint GEO satellite MAC/CAC scheme

Satellite networks present an attractive solution in providing worldwide access to the present and future generation multimedia communication services. However, the burstiness of multimedia traffic and the long propagation delays in Geostationary (GEO) satellite systems call for an efficient Medium Access Control (MAC) protocol and an equally efficient Call Admission Control (CAC) scheme, in order to provide acceptable Quality of Service (QoS) to multimedia users. This paper proposes a fair and dynamic CAC and MAC framework, named Fair Predictive Resource Reservation Access (FPRRA), which is based on accurate videoconference traffic prediction and makes decisions after taking into account the provider revenue. The framework’s performance is evaluated in comparison to other efficient schemes from the literature.     

基于协议转换的卫星通信系统的应用

探讨解决互联网到国际移动卫星C系统的通信协议转换问题。采用的方法是通过互联网的Telnet协议来仿真PSDN网络的X.25协议,通过2种协议的转换来实现互联网和卫星C系统的信息交互,并保持了原有用户直接使用X.25连接的访问习惯和指令集。采用X.25协议的单进程模式并结合虚拟多条电路方式对应互联网的多个Socket链接,该方法使得系统支持并发用户访问,并且提高访问速度和通信的稳定性。     

新时期应急卫星通信系统能力提升的改进研究

应急卫星通信系统是远程机动通信的主用手段,有时甚至是惟一手段。近年来,在抗震救灾、处突维稳特别是重要保障任务中通过卫星链路将图像、音频、数据、短消息等业务传输到远端指挥中心,实现远程应急指挥。该系统拥有专属卫星频段保障及专用网络通道,能够确保应对重大事件中信息传递的灵活性、便捷性、安全性。基于现有应急卫星通信系统进行了概述,剖析了新时期应急通信系统能力提升的集成必要性、集成原则,指出了应急卫星通信系统进一步提升通信能力的相关技术措施。     

基于DVB-RCS和WiMAX的卫星宽带无线接入体系设计

卫星宽带通信已成为目前研究的热点.现有的DVB-RCS卫星无线接入标准以物理层规范为主,尚未构成完整的卫星宽带无线接人体系.本文基于DVB-RCS技术,针对卫星宽带无线接入的需求和特点,结合地面WiMAX宽带无线接入技术,给出了卫星宽带无线接人体系的功能架构设计,并具体分析了各主要功能的设计与实现方法.     

卫星转发器增益衰减对转发式卫星导航通信系统入站链路性能影响分析

在卫星通信系统中,卫星是一个很重要的环节,卫星转发器的参数在一定程度上决定着整个系统的性能.转发式卫星导航系统是一个导航通信一体化的系统,通信系统中的微小卫星终端由于其发射天线波束宽,从邻星干扰方面考虑,远区卫星还处在微小卫星终端的主瓣内,因此发射功率受到了限制,是一个很明显的上行功率受限的系统.为了缓解对发射终端的压力,文中对卫星转发器的增益表减档对整个通信系统的性能影响进行了分析,得到的结果显示,在转发器增益衰减档减小时,整个系统的性能可以得到提高,试验结果也表明,对于微小卫星终端系统,卫星转发器的增益档设置在2dB左右比较适宜.