宽带卫星通信中的ACM技术

采用自适应编码调制技术(ACM)的卫星数字视频广播新标准(DVB-S2)应用到宽带卫 星通信网中,将极大提升系统吞吐量,提供更丰富的交互式业务。从实际应用的角度,分析 了ACM的控制机制并提出其编码调制方案的简化方法。仿真结果表明,在几乎不影响系统性 能的前提下,该方案可以大幅降低ACM机制的复杂度。     

ACM技术在DVB-S2 IP单播系统中的应用

研究并阐述了DVB-S2系统交互式应用中IP单播采用的自适应编码调制(ACM)技术,介绍了ACM的基本原理及实现过程,给出采用ACM的IP单播系统流程.     

IP技术在卫星通信中的应用及发展趋势

随着通信的发展,IP技术已经泛化,将IP技术与卫星通信相结合的卫星IP网络是通信领域众多研究的热点之一。该文针对卫星通信的传输特性,分析了卫星链路在Intemet应用中的特点,介绍了对卫星链路协汉的改进,给出了当前卫星lP网络技术的发展趋势。     

NAT重载技术在卫星通信IP业务中的应用

随着IP业务在卫星通信中的应用日益普及,卫星网络与地面网络互联互通已经成为必要。为了满足这种需求,并灵活配置,可以采用NAT重载技术提供较好的解决方案。本文探讨了NAT重载技术在卫星通信IP业务中的应用。     

优化卫星通信技术研究

卫星通信相关的费用包括固定投资和运行费用,从卫星通信经济学的角度出发,优化卫星通信可以节省成本。首先介绍了VSAT卫星通信网的网络拓扑及组网方式;其次从卫星通信的调制及编码技术两个方面分别对卫星通信进行优化,重点对格状编码调制、LDPC码、Turbo码与级联码编码技术、载波迭加技术进行了研究,并分别指出了各自的优点;最后对优化卫星通信技术的应用前景进行讨论。     

链路自适应技术在LTE中的应用

参照3GPP LTE的E-UTRA物理层规范,提出了一种链路自适应方案。实时调整传输功率以补偿信道的衰落,建立SNR-BLER曲线,在给定满足一定业务的目标BLER的条件下,找到各个MCS的SNR切换门限值,从而实现链路自适应。仿真结果表明,在保证通信质量的前提下,自适应方案比固定MCS有着明显的频谱效率增益,使无线资源得到优化配置;同时删减了频谱效率没有增益的MCS,降低系统复杂度。     

自适应编码调制技术在DVB-S2中的应用

阐述DVB-S2中自适应编码调制技术(Adaptive Coding Modulation,ACM)的原理,介绍DVB-S2自适应编码调制技术在IP单播中的具体应用,并分析影响ACM性能的因素.     

DPT技术在大庆宽带IP网中的应用

随着多媒体通信业务的发展,人们对信息的需求增长迅速,同时电视、电话已普及,电脑的家庭占有率也在不断提高,传统的电视、计算机、电话采用各自的物理传输网络,传输速率低,业务内容贫乏,已不能满足用户对宽带信息的需求,同时数字技术的全面采用使电话、数据、图像业务都可统一编码交换和传输,光通信技术的发展为综合传送各种业务、信息,特别是为宽带图像和高速数据业务提供了必要的带宽和可靠的传输质量;软件技术的发展使得网络所要求的特性和功能可以不必(或很少)改动硬件即可不断的变化和升级,技术的进步为宽带业务接入提供了有力的     

VoIP技术及其在宽带IP网的应用

本系统介绍了VoIP信令，语音压缩编码，静音检测，回声消除，IP语音传输和QoS保证等VolP核心技术，阐述了宽带IP网技术及其承载载实时多媒体业务的优势，探讨了VolP在宽带IP网的多种应用模式，并介绍了VolP在南京宽带IP网的开发和应用。     

认知无线网络技术在卫星通信中的应用

随着我国经济的迅猛发展，信息通信行业也迎来了极大地改革，不断增长的用户需求使得已有的通信频谱资源面临着储备不足的情况。而随着通信技术的更新换代，认知无线网络通信技术也逐渐走入我们的视线，而将认知无线网络技术与卫星通信有机结合的卫星认知无线网络技术在我国现今的通信领域中扮演着至关重要的角色。     

一种用于卫星通信的自适应编码调制信号接收方法

针对常规接收方法接收自适应编码调制信号时存在的接收过程易中断、数据不连续等问题,提出了一种适用于卫星信道的自适应编码调制信号接收方法.该方法通过采用统一的解调结构实现对不同调制信号的连续跟踪;利用接收端保存的帧同步字调制波形副本与接收信号中的帧同步字波形的相关结果,对解调方式切换时载波相位跳变值进行估计和补偿,解决了帧同步的连续跟踪问题.与现有方法相比,该方法不需要导频信号,可节省系统开销.     

Performances of adaptive modulation and coding in satellite mobile channel

Given that satellite mobile channel is a time-varying channel,Adaptive Modulation and Coding (AMC) was proposed to provide robust and spectrally efficient transmission over satellite mobile channel.Three different kinds of channel environment were considered in this paper:the urban area,the rural area,and the open space.Four combinations of modulation and coding were designed to meet reliable communication on time-varying channel,and spectral efficiency and system throughput of these three kinds of channel environment were simulated.Based on the simulation results,this paper analysed the results and compared the performances of AMC with non-AMC system in these three kinds of channel environment.At last,we come to the conclusions:a system with AMC can achieve higher spectral efficiency and better system throughput; and the spectral efficiency and system throughput of AMC system will be higher on better satellite mobile channel.     

Channel estimation and physical layer adaptation techniques for satellite networks exploiting adaptive coding and modulation

The exploitation of adaptive coding and modulation techniques for broadband multi‐beam satellite communication networks operating at Ka‐band and above has been shown to theoretically provide large system capacity gains. In this paper, the problem of how to accurately estimate the time‐variant channel and how to adapt the physical layer taking into account the effects of estimator errors and (large) satellite propagation delays is analyzed, and practical solutions for both the forward and the reverse link are proposed. A novel pragmatic solution to the reverse link physical layer channel estimation in the presence of time‐variant bursty interference has been devised. Physical layer adaptation algorithms jointly with design rules for hysteresis thresholds have been analytically derived. The imperfect physical layer channel estimation impact on the overall system capacity has been finally derived by means of an original semi‐analytical approach. Through comprehensive system simulations for a realistic system study case, it is showed that the devised adaptation algorithms are able to successfully track critical Ka‐band fading time series with a limited impact on the system capacity while satisfying the link outage probability requirement. Copyright © 2008 John Wiley & Sons, Ltd.     

Voice over IP service and performance in satellite networks

Voice over IP services have emerged as a low-cost alternative to PSTN voice service, and an attractive solution for voice/data integration in public and private networks. Satellite systems, as an integral part of the global communications infrastructure, already have an increasing portion of their capacities used to carry data packets, and with their global coverage and reach to remote areas are well positioned to enable growth of VoIP services. For VoIP over satellite, several issues need to be addressed. These include transmission and quality of service issues, as well as service-related issues such as service creation and customization, support of IN and supplementary services, and seamless integration with the PSTN. While the service-related aspects of VoIP are common to both terrestrial and satellite networks, transport-related issues are different. This article reports performance results of laboratory experiments for evaluating VoIP over satellite under different link and traffic conditions     

Dynamic uplink frame optimization with adaptive coding and modulation in DVB‐RCS2 satellite networks

In the current generation of satellite networks, modulation and coding schemes can be dynamically changed in real‐time to face different link conditions. Therefore, the link budget is not anymore required to be computed under the worst case, with relevant advantages in terms of efficiency. The new digital video broadcasting‐return channel via satellite 2 standard extends the dynamic modulation and coding to the return link: by using different modulation and coding schemes within the uplink frame, the terminals experiencing good link conditions transmit at very high bitrates, whereas the terminals experiencing fade events transmit at lower bitrates. This paper addresses the problem of optimizing the uplink frame modulation and coding schemes based on the current link conditions experienced by the terminals and on their transmission capacity requirements. The problem is formulated as an Integer Program and an efficient Linear Program approximation is proposed. Simulation results validate the proposed approach. Copyright © 2013 John Wiley & Sons, Ltd.     

自适应码率调整技术在动中通中的应用

在Ku频段移动卫星通信系统中,系统可用性是一个很重要的问题。因为与固定卫星通信系统相比,移动卫星通信系统中的地球站(动中通)在通信过程中是运动的,因此其通信的电磁环境是极其复杂的,存在多径衰落、多普勒频移、阴影效应和降雨衰减。着重分析了动中通中的这四个主要问题以及它们对系统可用性的影响,提出了通过自适应码率调整来提高系统可用性的措施。     

Standardization on performance objectives of satellite systems using adaptive coding and modulation

The radiocommunication part of the International Telecommunication Union (ITU‐R) establishes the standards for wireless communications. Recommendation ITU‐R S.1062 specifies the performance objectives for satellite communication systems providing constant bit rate service. However, this is not applicable to most modern satellite communication systems utilizing adaptive coding and modulation (ACM) schemes to compensate for channel impairments, especially for systems operating in high frequency bands. For this reason, ITU‐R recently developed Recommendation ITU‐R S.2131 that is suitable for satellite systems with ACM. The developed Recommendation provides a method to determine performance objectives for satellite systems using ACM. Two possible objective parameters are presented, including packet error rate and spectral efficiency. This paper presents the standardization process, and the background used to establish new performance objectives. In addition, interpretations of the objectives are given by using estimation results for two different propagation characteristics.     

Comparison of advanced coding and modulation schemes for multicarrier satellite communication systems

Digital satellite communication systems use coherent quaternary PSK (QPSK) as the preferred modulation scheme. In recent years, however, the search for bandwidth and power-efficient digital modulation methods has become an active research area. In this paper the performances of combined coding and modulation schemes employing multilevel signal alphabets are considered, in the framework of a system model which reasonably approximates the INTELSAT SCPC system. The main goal of the research was to investigate whether the efficiency of coded modulation schemes and their savings in transmitted power could be maintained in a system environment dominated by interference more than by the additive white Gaussian noise. A second goal was to compare the performance of signals with constant envelope, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel PSK, with that of signals allowing variations in amplitude, such as multilevel QAM. In the paper, we propose a channel model which is reasonably close to the real system, and a method for performance evaluation leading to an estimate of the asymptotic power gain of the modulation systems. The channel model and the method are applied to the analysis of coded 16- and 32- PSK and QAM.     

分布式无线通信系统中的自适应调制空时编码技术

考虑了应用线性离散码(linear disperse coding,LDC)的分布式无线通信系统中非等同调制方式的应用策略.在分布式MIMO(Multiple Input Multiple Output)系统中,通过分析大尺度衰落对传统LDC的后验信噪比(post-SNR]分布的影响,提出了一种偏移LDC的发送策略,这...     

Traffic management for TCP/IP over satellite ATM networks

Several Ka-band satellite systems have been proposed that will use ATM technology to seamlessly transport Internet traffic. The ATM UBR, GFR, and ABR service categories have been designed for data. However, several studies have reported poor TCP performance over satellite ATM networks. We describe techniques to improve TCP performance over satellite ATM networks. We first discuss the various design options available for TCP end systems, IP-ATM edge devices, as well as ATM switches for long-latency connections. We discuss buffer management policies, guaranteed rate services, and the virtual source/virtual destination option in ATM. We present a comparison of ATM service categories for TCP transport over satellite links. The main goal of this article is to discuss design and performance issues for the transport of TCP over UBR, GFR, and ABR services for satellite ATM networks