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     

DS－SFH扩频多址系统在瑞利衰落信道中多径分集的性能研究

本文讨论了混合ＤＳ－ＳＦＨ扩频多址ＳＳＭＡ通信系统在瑞利衰落信道中多径分集接收的性能。基于多径干扰、多址干扰和信道噪声之和为一个高斯随机变量的分析，推导了在等增益组合（ＥＧＣ）和选择最大（ＳＭ）多径分集接收算法下，扩频系统的平均差错概率。理论分析和数值模拟指出：扩频多径分集接收可以明显地改善ＤＳ－ＳＦＨＳＳＭＡ系统的性能，在提高系统性能方面，等增益组合算法优于选择最大分集算法。     

多径衰落信道下多功波CDMA信号的频率分集接收

本文研究了多载波码分多址（Ｍｕｌｔｉ－ＣａｒｒｉｅｒＣＤＭＡ）扩展频谱在系统在多径衰落信道下的频率分集接收技术，文中首先研究了理想载波恢复，频率选择性瑞利衰落信道条件下多功波码分址系统的性能，然后提出了用时间频率窗有来改善载波相位估计的算法，并对该算法在衰落信道下的性能进行了仿真，理论推导和计算机仿真结果表明，多载波码分多址系统的频率分集接收方案与理论上最佳的ＲＡＫＥ分集接收相比，性能略有下降，但     

在多径衰落信道下FD/SSMA系统的性能分析

多载波频率分集扩展频谱码分多址系统（ＦＤ／ＳＳＭＡ）是一种基于多载波传输,与直接序列扩展频谱码分多址系统（ＤＳ／ＳＳＭＡ）存在时间－频率对偶关系的扩频多址通信方案。在多径传输信道下,基于ＦＤ／ＳＳＭＡ信号的锐自相关和低互相关特性,本文提出ＦＤ／ＳＳＭＡ系统可以采用路径分集接收的方案。分析和模拟计算表明,在多径衰落信道下,采用路径分集方案时ＦＤ／ＳＳＭＡ系统的性能将得到明显的改善。     

降低码分多址移动通信系统中的衰落

降低码分多址移动通信系统中的衰落（金健青译，张洪达、王忆校）未来的移动通信系统将采用复杂的压缩技术，以在有限的带宽中传送更多的数据。近来，扩展频谱码分多址（ＣＤＭＡ）技术已引起人们的广泛重视。日本ＫＤＤ公司已采用分集技术来抑制多径衰落─－ＣＤＭＡ移动...     

DS—SFH扩频多址系统在瑞利衰落信道中多径分集的性能研究

本文讨论了混合ＤＳ－ＳＦＨ扩频多址ＳＳＭＡ通信系统在瑞利衰落信道中多径分集接收的性能，基于多径干扰、多址干扰和信道噪声之和为一个高斯随机变量的分析，推导了在等增益组合和选择最大多径分集接收算法下，扩频系统的平均差错概率，理论分析和数值模拟指出：扩频多径分集接收可以明显地改善ＤＳ－ＳＦＨ ＳＳＭＡ系统的性能，在提高系统性能方面，等增益组合算法优于选择最大分集算法。     

全数字线性调频信号产生及失真自适应接收机技术研究

对流层散射信道是一种随机多径信道,在该信道上传输数字信息时,首先要克服多径时散引起的码间干扰和快衰落导致的通信性能恶化。本文阐述了分离多径技术方案抗码间干扰、抗快衰落以及失真自适应接收的机理,研究了线性调频信号多径分集调制解调器的数字化实现,给出了系统性能测试的结果,积极有效地解决了散射信道存在的主要问题。     

在多径衰落信道上FD／SSMA系统的性能分析

多载波频率分集扩展频谱码分多址系统是一种基于多载波传播,与直接序列扩展频谱码分多址系统存在时间－频率对偶关系的扩频多址通信方案。在多径传输信道下,基于ＦＤ／ＳＳＭＡ信号的锐自相关和低互相关特性,本文提出了ＦＤ／ＳＳＭＡ系统可以采用路径分集接收的方案。分析和模拟计算表明,在多径衰落信道下,采用路径分集方案时ＦＤ／ＳＳＭＡ系统的性能将得到明显的改善。     

异步CDMA移动通信系统采用分集接收的多用户检测器

在ＣＤＭＡ移动通信系统中，多址接入干扰可以通过多用户检测技术来消除，而分集接收可以减小信道衰落的影响，本文给出了一类应用解相关检测，天线分集，ＲＡＫＥ多径分集技术的接收机，并对这一类接收机的性能做了分析，结果表明，在上行链路中，应用多用户检测和分集接收能够极大提高接收机的性能。     

大容量散射调制解调技术研究

简要介绍了时域自适应判决均衡器的原理,并根据对流层散射传播特点,利用自适应均衡技术以提高散射系统的抗码间干扰能力。采用四重显分集加自适应均衡的接收技术不仅可以减小码间干扰,收集隐分集能量,而且与显分集结合能够平滑信道选择性深衰落以及空间平坦衰落,大大提高设备通信能力。详细论述了自适应均衡器的技术特点和检测技术原理,并给出了对流层散射自适应均衡解调器的实现方案和抗多径测试结果。     

移动通信中基于智能天线的抗多径干扰技术

本文首先概述了多径信道传输特性,在此基础上,重点讨论了基于智能天线抗多径干扰技术的理论,并对基于ＣＭＡ算法的智能天线抑制多径干扰进行了计算机仿真。     

短波移动信道的仿真模型分析

在通信系统的研制和开发过程中,常常要考虑信道的传输特性,文中针对短波移动信道的特点,建立了小尺度衰落的短波移动信道的数学模型和计算机仿真模型,并对计算机仿真结果进行分析后,验证了该信道模型的可行性.该计算机仿真模型为比较各种抗多径衰落技术提供了一种有效的实验室仿真工具.     

WCDMA系统中基于多普勒频移估计的信道估计方法

Rake接收机是CDMA系统抗多径的有效手段，信道估计对其性能有很大的影响。传统方法是利用连续多个时隙的导频段估计出的信道参数，再对估计值进行平均。这种固定平均的方法不适合3G系统信道变化范围大的环境。本文提出了直接利用每个导频段的信道参数的包络来估计最大多普勒频移，再运用指数平滑法来调整各被估计时隙的权值的信道估计方法。仿真结果表明，该方法能准确有效地估计出信道参数，改善系统性能。     

OFDM系统信道估计和自适应分配算法的研究

在多径衰落的信道中,用固定调制方式的分配技术可能会造成OFDM系统资源浪费,考虑如何将自适应分配技术与OFDM相结合成为提高移动通信性能的关键技术。本文中提出一种基于动态信噪比SNR切换门限的自适应算法,该算法在保证通信质量所需BER的前提下,结合OFDM和PSK/QAM调制方式的优势,按照各个子信道的状态分配比特信息量和功率大小,使所需要的发射功率达到最优化。本算法能提高OFDM的频谱利用率,也能使系统获得更优的性能。     

The capacity for a discrete-state code division multiple-accesschannel

One of the proposed techniques for the third generation of mobile communications is code division multiple access (CDMA). Some attributes of CDMA which are important to indoor systems include desirable anti-multipath properties, the lack of a need for frequency management or assignment, coexistence with other systems and suitability for micro-cell and in-building systems. The anti-multipath feature turns out to be a key issue for indoor systems and derives from the property that a signal with path delay greater than one chip interval is treated much like an interfering user. The number of users that share the same spectrum, and still maintain an acceptable performance, is determined by the interference generated by the set of remaining users and leads to soft degradation as the number of users increases. This work describes and analyzes a model for the discrete-input continuous-output Gaussian multiple-access channel, that uses spread spectrum techniques. The notion of sum capacity is used to characterize the system performance. Bounds on the sum capacity of this essentially binary input, continuous output channel, where the variance of the output noise is dependent on the number of users present, are obtained. The users are noncooperative in that no common codebook or synchronization is assumed. A novel feature of the work is the use of the modeling of the activity of the user community as a birth-death process. An information theoretic approach is used and the sum capacity is then considered in light of the various regimes to determine the effect of this modeling     

Fading Channel Prediction for Mobile Radio Adaptive Transmission Systems

Adaptive transmission methods can potentially aid the achievement of high data rates required for mobile radio multimedia services. To realize this potential, the transmitter needs accurate channel state information (CSI) for the upcoming transmission frame. In most mobile radio systems, the CSI is estimated at the receiver and fed back to the transmitter. However, unless the mobile speed is very low, the estimated CSI cannot be used directly to select the parameters of adaptive transmission systems, since it quickly becomes outdated due to the rapid channel variation caused by multipath fading. To enable adaptive transmission for mobile radio systems, prediction of future fading channel samples is required. Several fundamental issues arise in the design and testing of fading prediction algorithms for adaptive transmission systems. These include complexity, robustness, choice of an appropriate channel model for algorithm validation, channel estimation and noise reduction required for reliable prediction, and design and analysis of adaptive transmission methods aided by fading prediction algorithms. We use these criteria in the review of recent advances in the area of fading channel prediction. We also demonstrate that reliable fading prediction makes adaptive transmission feasible in diverse wireless communication systems.     

Channel estimation and interference suppression for uplink CDMA mobile communication systems

Wireless communications for mobile telephone and data transmission is currently undergoing very rapid development. Code division multiple‐access (CDMA) implemented with direct sequence spread spectrum signaling is among the most promising multiplexing technologies for cellular telecommunications services. In this paper, jointly period inserted pilot symbols assisted recursive (PIPSAR) channel estimation and interference suppression techniques are proposed for uplink CDMA mobile communication systems. The uplink CDMA mobile communication system model is described in the form of space‐time domain through antenna array and multipath expression. Interference suppression is achieved by using adaptive minimum mean squared error (MMSE) digital filters that span several successive received chip oversampling vectors of a symbol interval. PIPSAR techniques are used to estimate channel parameters. The correlation between the successive periods is considered to further improve the performance of the proposed scheme. Analysis and simulations are used to evaluate the performance of the proposed scheme. Copyright © 2004 John Wiley & Sons, Ltd.     

Simulation issues for future wireless modems

Mobile communication systems present several design challenges that stem from the mobility of users throughout the system and the time-varying multipath channel and interference. To address these challenges, future wireless modems will rely on performance enhancing techniques such as adaptive antennas, DSP-based interference rejection techniques, and real-time signal processing for capacity improvement. The authors present an overview of key simulation issues for wireless communications systems. First, the burst error characteristics of the mobile channel require the selection of appropriate performance measures. Second, accurate simulations require realistic channel models that include the effects of attenuation, multipath propagation, noise, and interference. Third, link-level simulation of wireless systems requires attention to details of system implementation including the effects of nonlinearities. Finally, efficient simulation of CDMA systems may require a combination of analytic and simulation techniques     

自适应OFDM调制解调

OFDM以其频谱利用率高、抗多径干扰能力强等特点在高速数据通信领域获得了广泛应用,但是固定调制解调技术没有实现带宽资源的有效利用。自适应OFDM调制解调根据信道估计的结果对比特与功率进行动态分配以达到充分利用频带资源、提高系统整体性能的目的。对OFDM自适应调制解调的基本原理及其关键技术进行了较为全面的分析。     

基于子空间盲多用户检测算法的设计和仿真

随着数字移动通信技术的飞速发展,以码分多址(CDMA)为核心的第三代移动通信(3G)技术已经走入人们的日常生活。CDMA系统具有容量大、软容量、抗多径衰落强等优点,但多址干扰(MAI)的存在却严重的影响了系统的性能和容量,因此如何消除和抑制这种干扰就成了CDMA技术研究的热门话题之一,第三代移动通信系统已经将多用户检测技术(MUD)作为克服多址干扰的有效方法之一。文中主要研究了直接序列扩频码分多址(DS-CDMA)系统中的盲多用户检测算法,深入的研究了基于卡尔曼滤波的盲多用户检测算法,通过在卡尔曼滤波算法上引入子空间提高了原有卡尔曼滤波算法的效率。