卫星通信技术的发展

本文综述了卫星通信技术的若干进展及其发展趋势。主要涉及工作频段,通信卫星及地球站技术,调制与编码技术,多址技术,VSAT网,综合数字业务的卫星传输,卫星移动通信网,以及光纤通信的发展对卫星通信发展的影响等。     

专题：新型调制编码技术

现代通信系统的发展总是伴随着信道编码技术的突破与变革,例如在地面移动通信中,从2G使用卷积码、3G与4G使用Turbo码和多天线MIMO编码,发展到5G使用LDPC码和Polar码。面向下一代移动通信系统,包括高效抗干扰数据链、无人机通信、与6G融合的卫星通信等,研究新型编码调制方法是当前国际信息编码领域关注的重点,也是我国实现无线通信技术从跟跑、并跑到领跑的重大需求。我国已经正式启动6G技术研发,IMT-2020新技术工作组也已组织开展了新一代移动通信技术研究,新型编码调制仍然是其中一项关键技术。     

Ka频段卫星通信自适应传输技术

随着经济的日益发展,传统的C频段、Ku频段已经无法满足生活和社会活动的通信需求,因此带宽更大的Ka频段成为近年来的发展方向.由于通信信道条件对Ka频段卫星通信的影响很大,所以克服通信质量的干扰成为Ka频段通信的主要工作.本文在Ka频段卫星通信中给予LDPC码的自适应编码调制(ACM)技术及功率控制技术进行了研究.     

卫星信道编码技术及新发展

文中首先对卫星通信的信道特性进行分析,然后对广泛采用的卫星信道编码技术进行了描述和评价,重点讨论并分析了Turbo码、LDPC码、编码调制技术,串行级联编码和喷泉编码等新型信道编码技术的实现原理及性能,列举了各种新型信道编码技术在卫星系统中的应用情况及主要优点、不足.最后,展望了卫星信道编码技术的新发展方向.     

不同调制方式下高斯信道容量的计算

计算不同调制方式下的信道容量对实际通信系统的信道编译码设计具有重要的理论意义。首先从Shannon信息论出发,介绍了平稳无记忆连续信道与加性白高斯噪声信道容量的定义。接着利用互信息与微分熵的相互关系,推导了几种常用的不同调制方式下高斯信道的容量,并给出了相应的信道容量闭合计算表达式。通过将电力卫星通信信道模拟为高斯信道,对采用无速率信道编码联合不同调制方式的卫星通信进行了数值仿真。仿真结果显示,通过推导得到的闭合表达式计算信道容量,能对实际卫星通信的编码速率、译码启动条件的确定起到很好的理论指导作用。     

差错控制编码在卫星通信中的应用

本文回顾了差错控制编码在航天卫星通信中30多年来的发展概况,重点介绍和分析了CCSDS级联码标准及其改进译码方法。文中还对近来出现的Turbo码的原理与特性进行总结,分析了Turbo码在卫星通信中应用的主要问题     

宽带卫星通信信号调制识别及信道均衡技术研究

宽带卫星通信是现代通信系统中不可或缺的一部分。文中介绍了宽带卫星通信中的信号调制识别和信道均衡技术,这些技术可以提高系统的性能和稳定性,从而更好地应对卫星通信中的多路径干扰和时变失真等问题。在实际应用中,需选择合适的技术和算法对不同的信号调制类型进行优化和调整,进一步提高系统的性能和稳定性。文中为宽带卫星通信中的信号调制识别和信道均衡技术提供了参考,并为未来卫星通信系统的发展提供了支持。     

ACM技术在卫星通信IP网互联中的应用

自适应编码调制(ACM)技术根据信噪比自适应改变编码和调制方式,可将链路余量自动转换为链路传输能力,从而提高无线信道的频谱利用率。为解决卫星通信中IP化传输对电路带宽需求增加的问题,提出了应用自适应编码调制技术进行IP网互联的方案,通过对DVB-S2_ACM与VersaFEC_ACM两种不同技术的性能比较,分析了VersaFEC_ACM技术在岸船卫星通信IP网互联中应用的可行性及工作过程。链路计算与性能比较结果表明,该技术的应用可使岸船间原有的1 024 kb/s电路带宽利用率提高95%,同时抗信道衰落的余量提高6 dB,能够提高卫星通信资源利用率和系统可用度。研究结果可为后续工程应用提供参考。     

无线网络技术在卫星通信中的应用研究

无线网络技术是一种新型网络通信技术,从网络节点出发,实现信息存储转发和编码处理,实现对网络无线传输的优化。首先,文章介绍了无线网络技术的优势;其次,分析了无线网络技术对于卫星通信的作用;最后,重点探究了无线网络技术在卫星通信技术领域中的应用。     

级连码在卫星通信中的应用与RS码的译码

讨论卫星通信中的编码技术。根据卫星通信的特点与编码技术的主要作用,选用卷积码与RS码级连的方法来提高数据传输的质量与降低通信设备的成本。着重讨论RS码的编译码技术,在分析非系统RS码的过程中采用Blahut定理,获得一些新的结果。对有限域上的乘法,采用对偶基的概念使乘法器硬件实现非常容易,文中给出了求对偶基的算法。提出对著名的Berlekamp—Massey算法的改进。最后比较了系统RS码与非系统RS码译码的复杂性及其各自适用的场合。     

卫星通信中的信道编码与调制技术

本文首先研究了卫星通信中的信道编码与调制技术,并对广泛应用于卫星通信的DV B-S系列标准中的信道编码与调制技术进行了对比分析,最后提出了卫星通信采用更高级信道编码和调制技术的必然性。     

FDMA/DAMA卫星通信网资源分配策略研究

FDMA/DAMA卫星通信网的资源分配过程是为满足卫星链路高效、可靠使用卫星资源的综合决策过程。地球站参数、卫星参数、载波调制编码方式和雨衰等都是影响高效、可靠分配卫星资源的重要因素。在综合分析多种影响链路可用性因素基础上,提出了适用于FDMA/DAMA卫星通信网的资源动态分配策略,并设计了具体的分配流程和软件实现方案。通过比较某系统优化前后的运行数据,测试验证了优化分配策略的有效性和科学性。     

Adaptive coding and modulation scheme for satellite‐UMTS TDD systems based on a photogrammetric channel estimation method

The conventional wireless communication systems are designed to overcome the worst‐case channel, using the huge amount of redundant bits to assure communications performance and quality of services. Those systems cannot achieve the optimum spectrum and power efficiency. This paper presents an adaptive coding and modulation scheme used in the user terminals of the third‐generation satellite communication system. A three‐state photogrammetric channel estimation method is introduced for tracing the variations of large‐scale environments. The mobile user terminal dynamically switches the suitable coding and modulation schemes according to the result of photogrammetric channel estimator in order to maximize the power efficiency and data throughput. The real measurement data were used to validate our proposed method. The results show that the proposed method not only reduces the system complexity, but also mitigates the power control requirements and increases the data throughput for the land mobile satellite personal communication systems. Copyright © 2006 John Wiley & Sons, Ltd.     

The role of the Italian Space Agency in investigating high frequencies for satellite communications: The Alphasat experiment

Since the 1970s, satellite communications have been continuously evolving and improving to provide services characterized by increasing complexity and quality. This evolution has been supported by the constant increase in the operating frequency for achieving the necessary high data rates. This contribution focuses on the long‐term key role of the Italian Space Agency in supporting research activities on (and the developments of) high‐frequency satellite communication systems. The Alphasat experiment is the most recent effort of the Italian Space Agency, in collaboration with the European Space Agency, to thoroughly investigate the severe detrimental atmospheric effects impairing radio waves at high frequency (specifically, Ka and Q bands) and the associated fade mitigation techniques (eg, uplink power control, site diversity, and adaptive coding and modulation) required to achieve the typical target quality and availability of modern satellite communication systems.     

Adaptive coding and modulation for satellite broadband networks: From theory to practice

This paper presents the detailed design and the key system performance results of a comprehensive laboratory demonstrator for a broadband Ka‐band multi‐beam satellite system exploiting the new DVB‐S2 standard with adaptive coding and modulation (ACM). This complete demonstrator allows in‐depth verification and optimization of the ACM techniques applied to large satellite broadband networks, as well as complementing and confirming the more theoretical or simulation‐based findings published so far. It is demonstrated that few ACM configurations (in terms of modulation and coding) are able to efficiently cope with a typical Ka‐band multi‐beam satellite system with negligible capacity loss. It is also demonstrated that the exploitation of ACM thresholds with hysteresis represents the most reliable way to adapt the physical layer configuration to the spatial and time variability of the channel conditions while avoiding too many physical layer configuration changes. Simple ACM adaptation techniques, readily implementable over large‐scale networks, are shown to perform very well, fulfilling the target packet‐error rate requirements even in the presence of deep fading conditions. The impact of carrier phase noise and satellite nonlinearity has also been measured. Copyright © 2009 John Wiley & Sons, Ltd.     

卫星通信中的OQPSK调制技术分析

卫星通信系统的通信质量很大程度上依赖于所采用的调制方式。偏移正交相移键控(OQPSK:Offset Quadrature Phase Shift Keying)是在QPSK的基础上提出的一种恒包络调制技术。本文在详细介绍OQPSK调制技术原理和特点的基础上,分析了OQPSK调制技术的频谱特性及其在卫星通信中的优势,结果表明:OQPSK调制技术有良好的频谱效率、功率效率和抗非线性特性,非常适合卫星通信信道。     

网络编码技术及其在卫星通信中的应用

网络编码是网络通信的一种新技术,可以优化网络的传输性能,其基本思想是网络节点不仅可以进行存储转发,还可以进行编码处理,有别于传统路由的传输方式.文章介绍了网络编码的基本概念,分析了其在卫星通信中的研究和应用,并对其发展进行了展望.     

Transmission control protocol performance enhancement for mobile broadband interactive satellite communication system: a cross‐layer approach

Mobile broadband interactive satellite communication system is of great interest in both academic and industrial communities. However, the conventional strict‐layered protocol stack architecture and the standard TCP version perform poorly over satellite link. In this paper, we propose a comprehensive cross‐layer Transmission Control Protocol (TCP) optimization architecture while considering the main factors that affect the TCP performance. In our proposed architecture, we adopt two TCP split connection performance enhancing proxies to isolate the satellite link from the terrestrial part of the broadband satellite communication system. Then, based on the proposed cross‐layer architecture, we present an analytical model for the TCP throughput by taking the modulation and coding (ModCod) mode and the allocated bandwidth into account. In addition, we put forward a TCP‐driven bandwidth sharing and ModCod mode optimization algorithm to maximize the TCP throughput in satellite link. Extensive simulation results illustrate that our proposed comprehensive cross‐layer TCP optimization approach is able to improve the TCP throughput significantly. Copyright © 2014 John Wiley & Sons, Ltd.