共查询到18条相似文献,搜索用时 109 毫秒
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利用宽带卫星链路接入互联网是今后卫星通信的重要发展方向。首先介绍了基于宽带地球同步轨道(GEO,Geostationary Earth Orbit)网络移动的概念并以IPSTAR卫星为例建立模型,重点分析了基于宽带卫星移动通信的网络移动中的传输控制协议(TCP,Transfer Control Protocol)的特点,对TCP协议性能进行仿真模拟,最后分析了TCP协议在网络移动通信中的性能。结果证明,在宽带多媒体卫星移动通信中,由于系统允许信息传输具有较大带宽(IPSTAR中可以达到2 Mb/s),TCP传输的吞吐量和时延表现的较为稳定,因此,在基于宽带多媒体卫星的网络移动通信中实现TCP数据的传输具有一定的可行性。 相似文献
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由于卫星通信传输时延大,因此误码造成丢帧后,增加的传输时间严重影响卫星通信。针对卫星通信普遍采用的卫星数字视频传输协议(DVB_S),通过比较分析自动重传(ARQ)、选择性重传(SR_ARQ)和主动性重传(CA_ARQ)3种重传机制的误码率与丢帧率的关系,给出了3种情况的理论延时性能,理论推导和仿真结果都表明CA_ARQ重传机制性能最为稳定,延时最小,更加适合卫星信道应用。 相似文献
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分析了高速运动对TDMA卫星通信系统造成的影响,提出一种适用于高速运动环境的TDMA卫星通信同步控制技术。利用装载平台的导航信息辅助实现多普勒频偏的快速捕获,结合TDMA卫星通信特点完成多普勒频偏的跟踪补偿,同时使用多普勒频偏估计并修正运动引起的定时误差,可以在不改变TDMA卫星通信网现有其他设备技术状态的情况下,消除高速运动产生的影响,实现高速运动环境下TDMA卫星通信终端的快速入网和同步保持。 相似文献
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卫星TDMA通信是一种时分多址的通信联接方式,即划分不同的时隙以区别不同 的站址,因此TDMA对通信网络系统突发定时有严格的要求。TDMA卫星信道模拟器主要模 拟网络各节点(模块)、转发器之间的信号传输时序关系,以辅助系统设计及调试。描述TDMA 信道模拟器框图,模拟器FPGA数字电路设计,以及模拟器输入输出波形仿真等。 相似文献
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卫星ATM是近年来卫星通信领域的一个研究热点,TCP业务在卫星ATM中的传输是其中一个重要的研究课题.由于在TCP协议中主要是通过对窗口的控制来实现拥塞控制,而卫星信道传输的长延时特性大大降低了TCP层拥塞控制的效率.本文提出一种基于UBR传输的明确窗口指示拥塞控制策略,仿真结果表明在效率、公平性、VBR背景传输下的性能等各方面,取得了比目前广泛使用的Reno TCP更好的结果.并且该算法实现简单,交换机实现零信元丢失的缓冲区很小并且与TCP源连接的数目无关. 相似文献
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为解决地面通信网络与卫星通信的无缝连接问题,设计了一款基于IP的卫星通信终端.该终端由调制解调单元和IP接入单元组成,可以实现卫星通信的全IP传输.终端采用了TCP加速、中频调制解调和LDPC纠错编码等技术,具有路由选择、接入控制、频率可变及速率可变等功能,提高了IP数据在卫星信道传输的效率,有效地解决了地震、水灾等应急情况下卫星通信与地面通信网络互通问题. 相似文献
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介绍了一种卫星会议电视系统,它利用IBS/IDR技术进行业务信息传输,利用TDM/TDMA技术进行网控信息传输。重点介绍了卫星会议电视系统中的关键技术之一--网控技术,包括会议网管系统、卫星会议电视多点控制器和远端控制器、网控信道TDM/TDMA调制解调器、TDM/TDMA帧结构等,并对网控信道性能进行了分析。 相似文献
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《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1984,72(11):1637-1644
Nippon Telegraph and Telephone Public Corporation (NTT) initiated the world's first 30/20-GHz domestic satellite communication system for commercial use, using CS-2s launched from Japan in 1983. This system utilizes TDMA digital communication in the trunk transmission route of the public communication network, which includes interregional-center routes and main-island-to-remoteisland routes. Small transportable earth stations enable easy access to the public communication network from any place in Japan. The adoption of the 30/20-GHz band enables use of a compact on-board antenna that has a shaped beam that effectively covers the main islands of Japan. It also enables the use of high-performance, compact antennas at the earth stations. These antennas can easily be installed on the roof of telephone offices or set on motor vehicles. One apparent disadvantage of using the 30/20-GHz band is rain attenuation. However, NTT has realized a commercial system that is affected very little by rain attenuation. This was accomplished by utilizing high-performance radio equipment and by concentrating on appropriate system design. Adoption of the 30/20-GHz band is quite significant because the wide bandwidth available enables construction of high-capacity economical transmission systems. It also enables use of small antennas, which allow construction of high-speed digital direct-to-user transmission systems using small earth stations. These expand the application of the domestic satellite communication system to even small service areas. Therefore, NTT considers satellite communication to be of primary importance for its proposed digital communication network, and has begun research on a high-capacity, economical, multibeam communication satellite system using the 30/20-GHz band. This paper describes the 30/20-GHz band radio technology, digital communication technology utilizing high-speed TDMA, and operational technology in the public communication network. 相似文献
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Ohnuki M. Umehira M. Nakashima H. Kato S. 《Selected Areas in Communications, IEEE Journal on》1992,10(2):447-455
A system concept of a common alternative routing system is proposed for reducing total network costs by integrating satellite communications into public-switched networks, where satellite systems carry overflow traffic from terrestrial systems through common satellite channels. This concept has been realized by a satellite communication system called DYANET (dynamic channel assigning and routing satellite aided digital networks), which provides trunk circuits in combination with terrestrial systems. The key technologies developed for DYANET are a centralized network control system and a transponder hopping demand assignment TDMA (time-division multiple-access) system, to assure single-hop connection and to use satellite channel efficiently. The authors describe the system concept and configuration, the network control system, and the results of its commercial use 相似文献
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简要介绍了卫星移动通信系统的发展及分类,对影响静止轨道(GEO)卫星通信系统用户共享有限通信资源和有效利用卫星链路资源的多址接入方式进行了分析。主要从有效容量、实际应用和具体实现角度考虑分析比较,得到在GEO卫星通信系统中采用TDMA多址方式优于CDMA多址方式的结论。最后探讨了我国GEO卫星移动通信系统的现状和发展方向。 相似文献
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VSAT communications networks-an overview 总被引:1,自引:0,他引:1
The very-small-aperture-terminal (VSAT) fixed satellite communication network is a star network in which many dispersed micro terminals attempt to send data in a packet form through a random access/time-division multiple-access (RA/TDMA) satellite channel with transmission delay. The basic concept of the VSAT and its service potential are discussed. Two classes of traffic are addressed, namely business-oriented low-rate-data traffic and bulk data traffic of corporate networks. Satellite access, throughput, and delay are considered. The size of the network population that can be served in an RA/TDMA environment is calculated. User protocols are examined. A typical VSAT business scenario is described 相似文献
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Mosquera C. Scalise S. Taricco G. Garofalo G. Giunta D. 《Selected Areas in Communications, IEEE Journal on》2001,19(12):2310-2319
This paper studies the performance of the clock transfer scheme for burst-mode communication systems for which data are received during short, equally spaced intervals. Its main focus is on satellite-based time-division multiple-access (TDMA) communication systems with data regeneration and switching onboard the satellite, although the results apply to other TDMA systems as well. The system reference clock is generated onboard from an incoming, very stable ground source, based on a burst-mode demodulator that extracts the clock from a discontinuous modulated carrier due to the bursty nature of TDMA signals. If good enough, this onboard regenerated clock avoids the use of bulky and expensive clocks in the satellite payload and can act as the master clock of the TDMA system 相似文献