CDMA在卫星移动通信系统中的应用

首先简单介绍了移动通信系统和卫星移动通信的发展,重点说明了CDMA适合于卫星移动通信的系统特性,最后对应用于卫星移动通信系统的几种多址技术进行了比较,并简单介绍了CDMA在卫星移动通信系统中的应用情况。     

DS-CDMA卫星通信系统线性多用户检测算法性能比较

CDMA是新一代移动通信系统的关键技术,现代卫星移动通信也采用CDMA技术。多址干扰(MAI)的存在严重影响了CDMA系统的性能,需要采用多用户检测技术进行抑制。本文分析了卫星移动通信系统的模型,将线性多用户检测算法用于卫星移动通信系统,并对传统检测器、解相关检测器、MMSE检测器等线性检测器进行了性能比较。计算机仿真结果表明采用线性多用户检测技术使卫星移动通信系统的性能得到了明显的改善。     

中兴通讯CDMA实现A接口卫星传输

近日,由中兴通讯提供全套设备和解决方案的海南联通西沙CDMA网络覆盖工程完工,并通过卫星链路实现了岛上CDMA移动基站系统与大陆交换系统的信号传输。从技术角度讲,中兴通讯CDMA设备实现了对A接口卫星传输方式的支持。这是继“南海覆盖工程”完成沿海岸线近海覆盖之后,中兴通讯实现的又一具有重大现实意义的CDMA工程和技术突破,意味着远离大陆的岛屿内的CDMA移动通信将不再是困扰运营商的难题。将于近期开通的海南联通西沙CDMA网络,通过卫星传输解决了距离大陆近300海里的岛屿与大陆地面通信线路连接的困难。实际测试表明,采用A…     

CDMA联接卫星通信系统的容量分析

目前，采用多址技术的有卫星通信、移动通信、扩频通信、卫星移动通信等。本文就战术轻型同步卫星通信系统中采用码分多址（CDMA）联接技术的性能和优越性作了说明，并对采用CDMA联接的卫星通信系统的容量进行了综合分析。     

卫星导航定位系统在数字移动通信中的应用

通过对CDMA数字蜂窝移动通信系统中时间同步的研究，分析阐述了卫星导航定位系统在该领域的应用，并介绍了一种实现移动通信系统网络自同步的方案。     

卫星移动通信系统体系设计及应用模型

为发展我国的卫星移动通信业务,建设我国自己的卫星移动通信系统,针对卫星移动通信的特点,提出了一种卫星移动通信体系架构,从传输模型、通信体制和信令结构几方面时体系进行设计,通信体制使用COPSK调制方式,对功率放大器利用率高,减少用户对星上功率的要求从而增加系统的容量.信令结构使用3层传输模型,划分不同的逻辑信道,对不同的逻辑信道的信号速率,编码方式,编码率,使用频率等进行配置.并针对此系统提出了卫星移动通信的呼叫模型,作为卫星移动通信系统的应用模型,为卫星移动通信系统的实际应用提供参考.     

GEO多波束卫星移动通信系统多址方式选择的研究

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。     

地面功率流通量密度受限时卫星移动通信系统的容量

简述了卫星移动通信系统的特点,给出了相应的信道模型和功率控制的策略;从卫星辐射到地球表面的功率通量流密度的角度出发,用Monte-Carlo方法模拟和计算了CDMA和TDMA系统的效率,分析了多个CD-MA系统的相互兼容。     

中兴通讯CDMA实现A接口卫星传输

<正> 近日,由中兴通讯提供全套设备和解决方案的海南联通西沙CDMA网络覆盖工程完工,并通过卫星链路实现了岛上CDMA移动基站系统与大陆交换系统的信号传输。从技术角度讲,中兴通讯CDMA设备实现了对A接口卫星传输方式的支持。     

TDMA和CDMA第三代移动卫星通信系统主要技术比较

讨论了TDMA和CDMA第三代移动卫星通信系统(即第三代移动通信系统中的卫星移动通信网)一些主要技术,并考虑了其面临的一些主要问题及可能的解决方案。     

CDMA versus FDMA channel capacity in mobile satellite communication

At present a major effort is under way to define the most efficient modulation/multiple access system in mobile satellite communication. Where the emphasis is on digital voice modulation, the proposed multiple access methods almost always imply frequency division multiple access (FDMA). This analysis presents a comparison between FDMA and code division multiple access (CDMA), for the operation of both multiple access methods in the mobile satellite communication environment. The mobile satellites under consideration use multiple-beam or scan-beam antennas and employ frequency reuse of the allocated L-band frequency spectrum. As CDMA is better at absorbing Doppler and multipath effects, and permits higher rate coding, in general (practical considerations aside) it appears to be the more capable system.     

Adaptive antennas for MIMO OFDM‐CDMA communication systems

In this paper, we propose symbol‐based receivers for orthogonal frequency division multiplexing (OFDM) code‐division multiple‐access (CDMA) multiple‐input‐multiple‐output (MIMO) communications in multipath fading channels. For multiuser and multipath fading environments, both intersymbol interference and multiple‐access interference must be considered. We propose narrowband and wideband antennas and Wiener code filter for MIMO OFDM‐CDMA systems. The proposed receivers are updated symbol‐by‐symbol to achieve low computational complexity. Simulation results show that the proposed Wiener code filter can improve the system performance for the proposed adaptive antennas. The wideband antenna can achieve better error‐rate performance than that of the narrowband antenna when multipath effect exists. The convergence rate of the recursive least squares antennas is faster than that of the least mean square antennas. Copyright © 2013 John Wiley & Sons, Ltd.     

基于宽带CDMA的数据传输技术

随着移动的快速发展,基于宽带CDMA的数据传输应用变得越来越广泛。为深入掌握CDMA数据传输技术,介绍了宽带CDMA的总体结构及组成。对电路数据传输、短信传输方式以及分组数据传输的工作原理、工作流程及技术特点进行了详细分析,通过比较阐述了三者在数据传输方面的优缺点,并对不同数据传输方式的应用进行了探讨。为不同行业利用宽带CDMA传输数据提供了理论依据和技术参考。     

非静止轨道移动卫星通信中CDMA误码性能分析

分析了非静止移动卫星通信中ＣＤＭＡ的误码性能。考虑移动卫星的信道模型为有遮蔽的菜斯衰落模型，并将卫星覆盖的最小仰角对误码的影响引入到该模型中，推出了在高斯近似多址干扰下和最大似然二阶分集下，用户数、仰角和码长与误码的关系式，计算了数值曲线并讨论了结果。     

CDMA通信卫星系统容量分析

对基于码分多址(CDMA)体制的通信卫星系统及其容量进行了分析,从系统的角度,提出了CDMA体制的通信卫星系统容量的数学模型。定量分析了用户数量与系统的扩频增益、抗干扰能力指标、卫星转发器饱和功率等的关系,容量分析的结果可供人们在选择和设计通信卫星系统时参考。     

Teletraffic Analysis of an Overlaid System Using CDMA and TDMA With Cell Coverage Area Restriction

Wireless communication has emerged as the most promising and one of the leading sectors of the telecommunications industry in the 21st century. To appreciate the expansion of the wireless sector, in 1990, there were only ten million cellular phone subscribers worldwide that frequently use first-generation technology. Today, there are more than one billion subscribers, and it is expected to increase to more than three billion subscribers during 2007-2010. Attempting to more efficiently use the limited frequency bands available for mobile communications, the idea of overlaying a code-division multiple-access (CDMA) system on an existing narrowband system has been proposed and explored. The basic idea of a CDMA overlay is to allow wideband CDMA waveforms to share a common spectrum with narrowband conventional waveforms to take advantage of the unexploited bandwidth available in the narrowband systems. Theoretically, the separation of CDMA and narrowband waveforms can be accomplished through notch filters. However, the filtering techniques are not sufficient for eliminating the multicross interference problem. In this paper, as a means of reducing the interference that cannot be eliminated by the use of filters, we have introduced a new proposal of an overlaid system in which we reduce the coverage area of the time-division multiple-access (TDMA) interference slots (slots inside the CDMA bandwidth are henceforth cited as cochannel slots). With this new strategy, we significantly reduce the effect of TDMA interference over the CDMA system.     

Space-Time Optimum Combining for CDMA Overlay for Personal Communications Systems

The requirement to suppress narrowband interferences in CDMA communication stems from the overlay concept, i.e., coexistence of different types of signals in the same frequency band. This paper describes the performance analysis of a direct-sequence (DS) CDMA personal communication system sharing a common spectrum with narrowband microwave radio links in the 1.85 to 1.99 GHz band. The coexistence of these two systems within the same frequency band will improve the overall spectrum efficiency, but will also cause interference to both systems. In this paper it is shown that joint spatial and temporal optimum combining provides an efficient means of improving the performance of the DS-CDMA system through cancellation of the narrowband signal and the co-channel interferences. The proposed space-time architecture provides degrees of freedom for both diversity and interference cancellation. It is shown that the joint space-time receiver is robust with respect to the narrowband interference signal bandwidth and its carrier frequency offset from the DS-CDMA carrier frequency.     

码分多址系统的抗干扰分析

对于800MHz频段码分多址(CDMA)系统基站和直放站的杂散辐射对全球移动通信系统(GSM)900的干扰限制,信产部无(2002)65号文已作了明确规定。至于GSM900对CDMA的干扰,以及GSM1800和个人接入系统(PAS)等时分多址系统对第三代移动通信系统中宽带码分多址(WCDMA)系统的干扰影响有多大,文中以CDMA系统的抗干扰机理为基础,分析多系统共(站)址时这些干扰对CDMA系统容量的影响。工程实践中,通常采用滤波器来减少干扰对系统容量的影响,文中推导的公式可用来计算滤波器的衰减指标。     

低轨卫星自跟踪技术分析

针对低轨(LEO)卫星无信标信号时,传统自跟踪方式无法对其进行有效跟踪的问题,提出了全数字跟踪体制。对采用频分时分复合多址(FDMA/TDMA)体制的低轨卫星,采用宽带检测结合窄带跟踪的方法,快速准确地提取方位俯仰误差,实现了对目标卫星的高精度跟踪。对采用码分多址(CDMA)体制的低轨卫星,采用频域跟踪的方法,实现了低信噪比条件下对目标卫星的高精度跟踪。