移动卫星通信信道研究

分析了移动卫星通信信道的传输特征，建立并计算机模拟了移动卫星信道的统计模型，并在此基础上，建立了理想的Ｋ用户直接扩频码分多址（ＤＳ－ＣＤＭＡ）收发系统，研究其下行链路的误码性能。     

移动卫星通信信道模型的研究

本文着重分析研究移动卫星通信信道的传输特性，根据传输环境的不同，提出了三种不同的信道模型，并推导出相应信号包给的概率密度函数。     

陆地移动卫星通信信道的统计特性研究

陆地移动卫星信道的主要特点是多径衰落和阴影效应,同时由于移动体的运动将产生多普勒频移,本文假设阴影效应不仅影响直视波分量,同时也影响多径分量,建立了陆地移动卫星信道的分析模型,从多普勒功率谱的角度给出了振幅和相位的概率密度函数及自相关和互相关函数,并给出了电平通过率（LCR）和平均衰落持续时间（AFD）这两个高阶统计量,得出的结论比CHUN.Loo模型[1]物理意义更加明确,并给出了计算机仿真曲线。     

多普勒频移对低轨卫星通信抗干扰的影响

低轨卫星具有多普勒频移大的特点.对存在同频段干扰情况下,卫星信号和干扰信号的多普勒频移的规律及其对抗干扰性能的影响进行了分析.结果表明,当卫星运行至地面终端和干扰源之间时,卫星有用信号和干扰信号的相对频移尤其大,这就对低轨卫星通信中干扰的跟踪和抑制提出了更高的要求.     

一种针对短波多径信道的频移估计算法

短波通信由于其经济性、灵活性、适应性及抗摧毁性在军事通信中应用广泛。在短波多径信道条件下,多普勒频移对信号成分的功率衰减及符号相位的扩散,会影响数据信息正确解调。因此,需要研究针对多径信道条件下的频移参数估计。该算法主要应用于信号精确同步后,根据多径时延的估计范围进行划分,利用延时抽头线结构对接收训练序列进行等效,并对多径信道下的频移的最大似然估计进行推导。仿真结果表明,在ITU中等信道条件下,SNR为2dB时MSE性能可逼近CRLB,适用于短波通信中信号受到多径干扰时的频率估计。     

卫星通信中多普勒频移的快速捕获

本文提出了一种适用于低轨卫星扩频通信系统的多普勒频移快捕方法.该方法基于数字匹配滤波器及自动频率控制环路,利用数字匹配滤波器的PN码快捕特性及其输出主相关峰值对频偏的敏感性,缩短多普勒频移的捕获时间.论文首先推导了多普勒频移的平均捕获时间表达式,然后根据数值分析结果得到了准最佳捕获判决策略,最后通过比较验证了该快捕方法相对于传统串行捕获方法在性能上的提高.     

激光多普勒移频特性研究

为了提高激光多普勒测速系统的性能,增强系统与应用场景适配性,文中对比电光和声光两种主要移频器件的特点,从器件移频原理出发,提出了简化频率变换关系的分析方法,从理论上研究激光多普勒测速系统中两种器件产生的移频特性,搭建铌酸锂电光调制和声光移频全光纤激光测速系统链路,将测试频率特征与理论特征进行对比研究,提出一种新型声电混合调制激光多普勒测速系统。结果表明,该新型系统兼具声光移频测速系统可测量运动目标运动方向、运动速度,完成电光调制测速系统多频率校正的特点,频率测量相对误差较小,动态范围大。通过研究两种移频方式对频率特性,为设计高性能激光多普勒测速系统提供了理论和实验支撑。     

TDMA卫星通信系统中多普勒效应的分析及解决

本文提出了多普勒速率偏移的概念，将多普勒频移的量转化为多普勒速率偏移，从而建立了研究多普勒效应对ＴＤＭＡ卫星通信系统接口影响的分析方法，另外文中还提出了解决多普勒效应的转切换方法。     

一种基于多普勒频移的信道估计算法

为满足未来人们对移动通信越来越高的要求,实现真正意义上的无所不在,通信系统为用户提供更高速率的数据业务以及更好的用户体验,已成为当今移动通信技术发展的趋势.而准确的信道估计算法正是保证无线移动通信系统良好性能的关键所在.为此,首先介绍无线移动通信系统中信道估计的基本概念,其次介绍无线移动通信系统常见的信道估计算法,最后...     

移动衰落信道的计算机仿真模型

讨论了移动衰落信道特点,研究了移动衰落信道的模型,主要分析了模型中复乘性因子的产生方法,之后给出了产生该复乘性因子的计算机仿真模型,最后对于模型中有色高斯信号的产生进行了计算机仿真。     

全球移动通信频率分配情况分析

频率承载无线通信数据,在无线网络建设与发展中扮演着重要角色.及时并快捷地获得全球范围内移动通信所用频率的分配进展状况,将为国家制订相关频谱政策以及中国移动制订频谱使用战略提供重要的基础信息条件.本文整理归纳了全球范围内频率分配方面的相关信息,希望能为有关频谱管理、研究工作提供参考.     

A comparative analysis of frequency scanning and multispot beam satellite systems for mobile communications

A comparative analysis between frequency scanning and multispot satellite systems has been performed in the context of land mobile applications. The aim of the work has been to confirm the effectiveness of the frequency scanning approach, whose technical feasibility has already been proved by the authors in a previous study, also in a comparative investigation with a more conventional satellite configuration. A proper comparative methodology has been established to compare two baseline configurations of the two systems. The analysis has also been rendered parametric, varying some system characteristics such as bandwidth, traffic distributions and linearity requirement. The achieved results are provided and widely commented on in the paper.     

高动态卫星链路多普勒频移特性分析

为满足高动态卫星接收机设计仿真及测试需求,以高机动飞行器典型运动模型为参考,通过合理近似与简化,推导出高动态卫星信道多普勒频偏变化理论模型。仿真结果表明,理论模型的多普勒频偏计算误差小于6‰,适合工程设计应用。在此基础上,进一步分析了高动态卫星通信信号载波同步关键技术,并提出了解决方案建议。     

卫星通信技术的新发展

就当前卫星通信技术的若干热点作了一些概括和综述。首先,介绍了宽带卫星通信系统的有关概念和发展现状,提出了需解决的主要技术问题,给出了典型应用;然后,在介绍卫星移动通信的国内外发展现状的基础上,研究了系统的特点及需要突破的关键技术;最后,介绍了空间通信网的基本概念,给出了网络组成及功能,分析了需要解决的若干新技术。     

COMETS experiments for advanced mobile satellite communications and advanced satellite broadcasting

The Communications and Broadcasting Engineering Test Satellite (COMETS) was developed to evaluate Ka‐band (31/21GHz) and millimetre‐wave (47/44 GHz) advanced mobile satellite communications systems, 21GHz advanced satellite broadcasting systems, and S‐band and Ka‐band inter‐orbit satellite communications systems. COMETS was launched because it was to become the new ‘bridge’ toward advanced satellite communications technologies in the next century, but the launch on 21 February 1998 regretfully failed due to premature shut down of the second stage engine of the H‐II launch rocket. After this accident, the initial low elliptic orbit of COMETS was improved by the apogee engine to a larger elliptic orbit with an apogee altitude of 17711km, a perigee altitude of 473 km, an inclination of 30.1°, and an orbital period of 319 min. Original and modified COMETS experimental plans, countermeasures in earth stations for the orbiting satellite, as well as an overview of the COMETS satellite and ground terminals are presented. Copyright © 2000 John Wiley & Sons, Ltd.     

A channel state‐driven ACM algorithm for mobile satellite communications

The last decade has been characterized by an increasing demand of higher throughput and more reliable communication links for supporting multimedia applications. To this aim, the focus has been toward both broadband and broadcast solutions providing multimedia services to mobile users. In order to exploit such advanced services, ubiquitous and efficient mobile connections are required: satellite communications (SatCom), able to cover low density populated areas and to fill terrestrial coverage gaps, are a viable solution, as long as capacity is properly optimized. Waveform adaptation can be considered as one of the reference approaches for increasing the throughput and the reliability in wireless communication links. However, the large round trip time and user mobility in SatCom scenarios represent a serious challenge that limits the effectiveness of transmission parameters adaptation. In this paper, we focus on a novel state‐driven adaptive coding and modulation approach aiming to predict the most suitable modulation and coding scheme for each communication state, based on channel state estimation and a Markov propagation model. The paper introduces the concept of state estimation decision reliability and transmission reliability. Different from other approaches, the state‐driven algorithm allows to increase the system reliability by lowering the outage probability in the selected scenarios. The effectiveness of the proposed approach has been validated by resorting to numerical results after a careful parameter optimization. Copyright © 2015 John Wiley & Sons, Ltd.     

A survey on mobile satellite systems

Satellite systems represent a significant solution to provide communication services to mobile users in under‐populated regions, in emergency areas, on planes, trains, and ships. In all these cases, satellite systems have unique capabilities in terms of robustness, wide area coverage, and broadcast/multicast capabilities. This paper surveys current mobile satellite networks and services from different standpoints, encompassing research issues, recent standardization advances (e.g. mobile extension for DVB‐S2/‐RCS, DVB‐SH) and some operational systems (e.g. Globalstar, Inmarsat BGAN, Iridium, and Thuraya). The last part of this paper is devoted to qualitative and quantitative comparisons of the different mobile satellite systems to understand their characteristics in terms of services, capacity, resource utilization efficiency, and user mobility degree.Copyright © 2009 John Wiley & Sons, Ltd.     

卫星通信的近期发展与前景展望

从分析卫星通信的特点入手,综述了卫星通信的卫星平台、可用频率资源和主要相关技术的发展状况,概述了典型的卫星通信系统的性能特点,介绍了卫星通信的应用及产业化发展情况,并展望了发展前景。     

Accurate estimation of Doppler shift in mobile communications with high vehicle speed

Representing the channel varying rate and the mobile speed of a mobile terminal directly, Doppler shift is an important parameter in vehicular mobile communications and therefore is widely used in mobile target detection and adaptive applications. Hence, this paper puts forward an accurate Doppler shift estimator in mobile communications with high vehicle speeds, which can also be treated as a vehicular speed estimator due to the well‐known relation between the Doppler shift and the mobile speed. Specifically, the proposed estimator is based on the channel level crossing rate, and an iterative process is presented to achieve signal‐to‐noise ratio (SNR) insensitive estimates in accordance with the level crossing rate estimation error analysis. Moreover, we prove the convergency of the iterative Doppler shift estimator in theory. Computer simulations conducted under a wide range of noise corruption clearly show that the proposed estimator substantially outperforms several existing estimators in terms of accuracy and achieves a good SNR‐insensitive performance in a wide range of velocities and SNRs. Copyright © 2013 John Wiley & Sons, Ltd.