UHF、L频段陆地卫星移动通信业务遮蔽环境衰落研究

ＵＨＦ、Ｌ频段路边树遮蔽和多径衰落实验分别于１９９９年８月和９月在河南安阳境内进行。利用日本ＧＭＳ１４０Ｅ气象卫星为信标,其下行频率分别为４６８．９２４ＭＨｚ和１６９１．００ＭＨｚ,有效全向辐射功率分别为３７ｄＢｍ和５６ｄＢｍ,中频带宽分别为２ｋＨｚ和２００ｋＨｚ,极化方式均为线极化。地面接收系统和数据处理设备安置于汽车上。此项实验的目的是为地面卫星移动通信系统的设计提供重要的信道参数。本文给出了     

山区UHF频段陆地移动卫星通信系统多径衰落测量

ＵＨＦ频段山区多径落衰实验于１９９９年７月在石家庄至山西阳泉高速公路及河南林州至山西上党方向公路上进行。利用日本ＧＭＳ１４０Ｅ气象卫星为信标,地面接收系统和数据处理设备安置于汽车上。测试在卫星和接上机之间不被阻挡时进行。此种情况下可保证信号衰落或增长主要早由于多径而造成的。这里讨论的一个主要问题是：山区多径和路边树蔗蔽衰落在地面移动卫星通信中衰落幅度的大小。路边树衰落在时间百分比为１％和５％时分别     

美国UHF频段卫星移动通信系统初探

美国自上世纪70年代开始即发展UHF频段卫星移动通信系统,先后建设了FLTSATCOM、UFO等UHF频段卫星移动通信系统,以及近年来正在建设的MUOS卫星移动通信系统。美国UHF频段卫星移动通信地面终端及技术体制也在不断演进,技术体制从早期的FDMA、发展到TDMA,直至近期的WCDMA技术,达到地面三代移动通信的技术水平。终端从早期仅支持大型作战平台,发展到支持小型化低功耗的多模手持终端。文章详细论述了美国UHF频段卫星移动通信系统的发展历程、典型的UFO系统概述、终端设备以及体制波形。     

码分多址数字移动通信的抗多径衰落技术

移动信道的主要特征是由于移和多径传播的多径落现象，本文首先概述了码分多址（ＣＤＭＡ）数字移动信道的数学模型，并在此基础上讨论了ＤＳ－ＦＳＨ扩频多系统在瑞利衰落信道中的多径分集接收技术的性能，推导了基于最大合并（ＭＲＣ）等增益组合（ＥＧＣ）和选择最大（ＳＭ）多径分集接收算法下，扩展系统的平均差错概率，理论分析和数值模拟表明，扩频分集技术可以明显地提高ＣＤＭＡ系统的抗衰落能力，并且指出ＭＲＣ优于ＥＧＣ     

陆地移动通信中多径传播的径数分布

本文分析了陆地移动通信中多径传播的径数的随机性,发现径数的变化服从线性生灭过程,导出了这一随机过程的分布律,所得结果用于多径时延分析和多径信道的模拟研究已取得成效。     

卫星移动通信中的抗多径衰落技术

在移动卫星系统中，多径衰落是影响通信质量的重要因素之一。本文对目前在移动卫星中应用比较广泛的抗多径衰落技术进行了归纳与总结，并分析了四种的典型的抗衰落技术，最后给出了选择抗多径衰落技术方案的一般性原则。     

陆地移动通信多径传播的实时模拟技术研究

根据移动无线信道多径传播的特点，提出一种径衰落信道实时模拟技术，利用该技术，已制成实时多径衰落信道模拟器，它可作为移动通信系统的测试仪器在室内对通信设备进行信道传输测试。     

数字移动通信中的抗多径衰落技术

移动信道的主要特征是由移动和多径传播所产生的多径衰落现象。在高速移动通信系统中，必须采用抗多径衰落技术，才能实现有效传输。本文首先概述了移动信道的数学模型及其典型形式，在此基础上，分别讨论了时分多址（ＴＤＭＡ）和码分多址（ＣＤＭＡ）系统的抗多径衰落方法──自适应信道均衡技术及多径分集接收技术，并简述了近年来较为活跃的多用户检测技术和自适应天线分集技术。     

GPS系统中的多径效应分析

本文研究了ＧＰＳ系统中多径效应的伪唬测量误差，先分析镜面多径信号的时间延迟和由此引起的频带扩展，然后研究在用相干和非相干延时锁定环跟踪ＰＮ码信号时多径信号对Ｓ曲线的影响和由此带来的伪距测量误差（多径误差）以及减小多径误差的方法。     

陆地移动通信多径传播中电波径数的分布及模拟

本文根据ＶＨＦ、ＵＨＦ陆地移动通信中电波传播的实际特点，考虑了电波径数变化为一个有限容量状态空间的生灭过程，导出了多径传播中电波径数的分布模式，其理论值与实验测量结果一致性较好。本文还对移动接收电台运动过程中电波径数的动态随机变化进行了计算机模拟，给出了具体的模拟方法和结果。     

Ku频段地面移动卫星多媒体传输系统分析

介绍了一种宽带Ku频段地面移动卫星多媒体传输系统。对地面移动卫星通信地球站特点进行了分析。针对3种天线口径进行了卫星链路计算，并对计算结果进行了分析。     

Roadside tree attenuation measurements at UHF for land mobile satellite systems

Tree attenuation results at 870 MHz are described for experiments conducted in October 1985 and March 1986 in Central Maryland. These experiments employed a helicopter as a source platform and a van with receiver and data acquisition instrumentation. Tree attenuation results were obtained for the cases in which the van was stationary and in motion. The experiments were performed for the purpose of providing the designers of planned land mobile satellite systems with important elements in the determination of link parameter requirements; namely, the expected fading statistics due to roadside trees for both mobile and stationary vehicles. Single tree attenuation results gave worst case median fades as high as 15 dB although roadside tree values were noted to produce fades in excess of 20 dB for small percentages of time. The cumulative fade distributions and their relative contributions as a function of path elevation angle, right side versus left side driving, and different road types are derived from the field measurements. Upon comparing the attenuations from bare deciduous trees (March 1986) with those due to trees in full foliage (October 1985), the increase in dB attenuations were, in general, less than 25 percent for the dynamic cases, and less than 40 percent for the worst case static configuration. This result demonstrates thai the dominant fading is caused by the wooded tree branches as opposed to the leaves on these branches. The tail end of the observed fade distributions was observed to follow lognormal distributions with respect to dB attenuation.     

Review of generative models for the narrowband land mobile satellite propagation channel

The land mobile satellite (LMS) propagation channel is frequently described using statistical models. These models usually make different assumptions regarding the behavior of the direct signal, the diffuse multipath component and the shadowing effects. This paper analyzes the theoretical formulation and implementation of time‐series synthesizers based on three typical statistical models: Loo, Corazza–Vatalaro and Suzuki, describing their similarities and differences. The discussion is not limited to the amplitude of the complex envelope but also to the phase variations and Doppler spectra. Finally, guidelines are also provided for comparing model parameters supplied by different authors. Copyright © 2008 John Wiley & Sons, Ltd.     

Efficient estimators for the land mobile satellite channel

A novel class of adpative Kalman channel estimators (AKCEs) for low-data-rate signalling via the land mobile satellite (LMS) channel is presented in this paper. The proposed technique is based on a scheme known as the ‘parallel processing algorithm’ and assumes a discrete Gauss–Markov extension of the LMS channel model. Three different approaches compared against the non-adaptive filter show an improved estimation error variance under various environmental conditions. Trading off computational complexity and performance, the derived maximum a posteriori (MAP) approach has been found to be best applicable. © 1998 John Wiley & Sons, Ltd.     

Land mobile satellite communication channel model for simultaneous transmission from A land mobile terminal via two separate satellites

There are certain data services that could use transmit-only land-mobile satellite communication terminals. Such terminals would not be able to receive acknowledged messages and transmit them onward. Thus it is of interest to study alternative means of improving the system reliability. In this paper we propose the use of transmission to two satellites separated in azimuth and elevation in order to improve the reliability of throughput. We have investigated the improvements by building upon the model proposed by Lutz for land mobile satellite communications via one satellite, and extended this using measurements of the shadowing coefficient in different areas (suburban, countryside and city) to two separated satellites. The measured data is used to produce an empirical model of the equivalent shadowing coefficient variations with the separation angle variation between two satellites. The results show good agreement with the shadowing coefficients produced by the Lutz model for a single satellite. The degree of improvement produced by using two separated satellites in the different environments, in terms of bit rate and probability of the received power is given.     

Predictive relay‐selection cooperative diversity in land mobile satellite systems

Cooperative diversity protocols promise a new dimension of diversity that provides better communication by engaging nearby relays in forming a ‘virtual’ array of antennas for combined signal transmission. The current incremental cooperative diversity algorithms incrementally select best relay(s) to cooperate based on the channel quality reported by the relays. However, the algorithms do not take into consideration the fact that the chosen best relay(s) at estimation may not always be the best at the time of communication. This is due to the time delay between the relay selection and its transmission of signal (problem of outdated channel quality information (CQI)). To solve this problem, the concept of channel prediction is introduced and employed whereby each relay determines a predicted value of its CQI based on its past measurements. The paper therefore develops a novel predictive relay‐selection (PRS) cooperative diversity model that seeks to improve land mobile satellite communication through prediction protocols. In the model, the chosen best relay is the one with the best predicted CQI value instead of the traditional outdated one. Performance analysis of outage probability and average bit error probability for the newly developed PRS cooperation shows that the PRS cooperation is better than direct and outdated CQI relay communication. Copyright © 2015 John Wiley & Sons, Ltd.     

Multipath Fading Channel Simulation for Mobile Satellite Communication System

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