导频比和多普勒频移对OFDM系统影响的研究

参考无线多径信道中的COST-207信道模型,选取COST-207模型中的典型城市环境针对不同导频比与不同多普勒频移频率对基带OFDM通信系统性能的影响进行了仿真分析.从仿真结果得出使用块状导频形式的OFDM系统容易受多普勒频移与时间选择性信道变化的影响.同时当信噪比达到一定程度后,子载波间干扰是构成系统噪声的主要部分.而梳状导频虽然在性能上不如块状导频,但在对抗多普勒频移与时间选择性衰落信道方面相比块状导频具有一定的优势.     

TDD相位预均衡OFDM系统中的定时误差分析

研究了在多径瑞利衰落环境中，抽样定时误差对相位调制的时分双工(TDD)预均衡正交频分多路复用系统(OFDM)的误码率性能影响．给出了理想和非理想相位预均衡处理的误码率解析表达式，并进行了计算机仿真，仿真和理论分析相符．对于TDD相位预均衡OFDM系统，定时误差导致了解调数据的相位旋转，且系统性能随定时误差的增加呈加速恶化的趋势．与无定时误差的瑞利衰落性能上界相比，当归一化定时误差为1／8时，理想和非理想相位预均衡的性能分别损失了约1dB和3dB；归一化定时误差为1／4时，二者的性能均严重恶化且差距减小，这时候定时误差成为影响系统性能的主要因素．     

OFDM移动通信系统中的最大多普勒估计

提出了一种基于信道估计自相关函数的多普勒频移估计算法.在OFDM符号数据段前插入正交可变扩频因子(OVSF)序列,求出时域的信道冲激响应,利用信道冲激响应的自相关实现多普勒频移估计.仿真结果表明,该算法可以在较大多普勒频移范围内有效地估计出多普勒频移.     

移动通信中一种精确的多普勒频移估计方法

该文利用有效到达径上信道参数的估计值,统计其包络的电平通过率(Level Crossing Rate,LCR),据此估计出时变多径信道的多普勒频移。同时还在理论上分析了噪声环境下LCR方法的估计偏差,进而提出了精确的改进方法,使得通信系统在各种移动速度和信噪比下都具有较高的估计精度。     

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。     

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...     

基于特定导频OFDM信道估计的研究

在OFDM系统中,准确的信道估计是对抗瑞利衰落信道中信道干扰的关键。提出了一种对OFDM信道估计的新方法,利用CR Spline函数的插值方法,设计一个特定的导频结构,从而导出信道估计的CR Spline函数形式,用该函数近似信道衰落包络。实验结果表明,仅用少量导频就可以近似出信道特性,并具有良好的平滑性。计算机仿真证明了提出算法的有效性。     

多普勒频移对CDMA系统信道容量影响的分析

文章介绍了CDMA系统中信道容量的分析方法。结合某CDMA系统设计,分析和仿真了多普勒频移对CDMA系统信道容量的影响。     

WLAN OFDM系统信道估计技术

介绍了802．11a系统的信道估计技术，包括LS(最小平方)信道估计技术，维纳滤波器方法，以及它们的基本原理和主要算法．在802．11a系统的仿真平台上用LS和维纳滤波器方法分别对信道进行估计．仿真结果表明，对瑞利衰落信道，在相同的传输速率下，Wiener-Filter的信道估计比LS信道估计都有一定的性能提高。     

复杂环境下基于噪声匹配的最大多普勒频移估计

本文针对城市复杂信道环境下的最大多普勒频移估计需求,根据莱斯衰落信道中电平通过率(LCR)算法的理论推导,提出了一种基于噪声匹配的最大多普勒频移估计算法.所提算法通过对接收信号进行低通滤波处理,实现干扰噪声与多普勒检测器之间的匹配,从而有效提高最大多普勒频移的估计性能.而且基于莱斯衰落信道下最佳滤波比值的分析和推导,得...     

单载波频域均衡与多载波OFDM误码性能的理论比较

单载波频域均衡(SC-FDE)和多载波正交频分复用(OFDM)是数字通信中用于克服多径衰落的两种技术。本文通过理论推导对这两种技术在高斯白噪声通信信道巾的误码性能进行了比较。利用高斯分布尾部概率的数值变化特性,本文推导出如下结论:在低信噪比条件下,OFDM的误码性能略优于SC-FDE,而在高信噪比条件下,SC-FDE则能取得显著优于OFDM的误码性能。这一结论对于通信系统的设计具有重要的参考价值。     

Pre-equalization Techniques for Downlink and Uplink TDD MC-CDMA Systems

Time division duplex (TDD) multi carrier-code division multiple access (MC-CDMA) systems have recently been proposed as potential candidates for next generation (4G) technology. In order to mitigate multiple access interference, in this paper we investigate pre-equalization schemes for both downlink and uplink transmissions, the former also in a multiple transmit antenna scenario. In particular, new pre-equalizer techniques are introduced and complexity issues addressed. Numerical results are given to highlight the effectiveness of the proposed schemes with respect to other existing pre-equalizer solutions. Paola Bisaglia was born in Padova, Italy, on August 8, 1971. She received the Laurea (cum laude) and Ph.D. degrees in electronic engineering from the University of Padova, Padova, Italy in 1996 and 2000 respectively. In 2000 she joined Hewlett-Packard Research Laboratories, Bristol, England, working on Home Phoneline Networking and wireless LANs. From 2002 she is a research fellow at the Department of Information Engineering of the University of Padova, Italy. Her research interests include wireless local area networks; modulation, coding techniques and detection strategies for next generation (4G) broadband cellular systems, based on the combination of multi-carrier and spread-spectrum modulations. Luca Sanguinetti is a Ph.D. Student of the University of Pisa. He was born in Empoli, Italy, on February 19, 1977, and he received the Doctor Engineer degree (cum laude) in information engineering from the University of Pisa, Italy, in 2002. Since 2002 he was with the Department of Information Engineering of the University of Pisa, where he is working toward the Ph.D. degree in information engineering under the supervision of Prof. Umberto Mengali and Prof. Michele Morelli. In 2004, he was a visiting Ph.D. student at the German Aerospace Center (DLR), Oberpfaffenhofen, Germany. Currently he is involved in a research project dealing with the design and the development of base stations and user terminals for wideband wireless communications systems able to cope with those reconfigurability and interoperability characteristics required by the next generation mobile communication systems. His research interests are in wireless communication theory, with emphasis on synchronization and detection algorithms and channel estimation in multiple-access communication systems. Michele Morelli received the Laurea (cum laude) in electrical engineering and the “Premio di Laurea SIP” from the University of Pisa, Italy, in 1991 and 1992 respectively. From 1992 to 1995 he was with the Department of Information Engineering of the University of Pisa, where he received the Ph.D. degree in electrical engineering. In September 1996 he joined the Centro Studi Metodi e Dispositivi per Radiotrasmissioni (CSMDR) of the Italian National Research Council (CNR) in Pisa where he held the position of Research Assistant. Since 2001 he has been with the Department of Information Engineering of the University of Pisa where he is currently an Associate Professor of Telecommunications. His research interests are in wireless communication theory, with emphasis on synchronization algorithms and channel estimation in multiple-access communication systems. Nevio Benvenuto received the Laurea degree from the University of Padova, Padova, Italy, and the Ph.D. degree from the University of Massachusetts, Amherst, in 1976 and 1983, respectively, both in electrical engineering. From 1983 to 1985 he was with AT&T Bell Laboratories, Holmdel, NJ, working on signal analysis problems. He spent the next three years alternating between the University of Padova, where he worked on communication systems research, and Bell Laboratories, as a Visiting Professor. From 1987 to 1990, he was a member of the faculty at the University of Ancona. He was a member of the faculty at the University of L'Aquila from 1994 to 1995. Currently, he is a Professor in the Electrical Engineering Department, University of Padova. His research interests include voice and data communications, digital radio, and signal processing. Silvano Pupolin received the Laurea degree in Electronic Engineering from the University of Padova, Italy, in 1970. Since then he joined the Department of Information Engineering, University of Padova, where currently is Full Professor of Electrical Communications. He was Chairman of the Faculty of Electronic Engineering from 1990 to 1994, Chairman of the PhD Course in Electronics and Telecommunications Engineering from 1991 to 1997 and Director of the PhD School in Information Engineering from 2004. Also, he was member of the programming and development committee from 1997 to 2002 and member of Scientific Committee from 1996 to 2001 of the University of Padova; member of the budget Committee of the Faculty of Engineering from 2003. He has been actively engaged in research on: Digital communication systems over copper wires and fiber optics; Spread spectrum communication systems; Design of large reliable communications networks; Effects of phase noise and HPA nonlinearities in OFDM systems; 3G mobile radio communications systems (UTRA-FDD and TDD) and beyond 3G (OFDM modulation and MC CDMA); Packet radio, Ad-hoc networks with the use of Bluetooth and WLAN. He was Chairman of the 9-th and 10-th Tyrrhenian International Workshop on Digital Communications devoted to “Broadband Wireless Communications” and to “Multimedia Communications”, respectively, and he was General Chair of the 7th International Symposium on Wireless Personal Multimedia Communications (WPMC'04). He spent the summer 1985 at AT&T Bell Laboratories on leave from Padova, doing research on digital radio systems. He was Principal investigator for research projects entitled “Variable bit rate mobile radio communication systems for multimedia applications”, “OFDM Systems with Applications to WLAN Networks”, and “MC-CDMA: an air interface for the 4th generation of wireless systems”.     

基于LDPC码的OFDM系统性能分析

正交频分复用(OFDM)是一种多载波调制技术,已成为实现高速数据传输的主流技术,在无线局域网、HDTV中得到广泛应用;低密度奇偶校验(LDPC)码是一种译码复杂度低的纠错码,可获得接近香农限的优异性能。本文提出了结合LDPC码的COFDM系统方案,阐述了相关原理,对其性能进行了仿真分析,比较了在不同调制方法下系统的性能差异,并将基于LDPC码和Turbo码的COFDM系统在不同信道中的误码性能进行了对比。仿真结果表明,基于LDPC码的COFDM系统在提供较高比特传输速率的同时也具有良好的纠错性能。     

Performance of Hybrid ARQ Schemes for OFDM Systems

In this paper,four schemes of Hybrid Automatic-Repeat-Request(HARQ)for Orthogonal Frequency DivisionMultiplexing(OFDM)systems are evaluated when they are used in different channel environments.The AccumulativeCorrect Packet Reception Rate(ACPRR)performance of four HARQ schemes is compared in order to verify which ARQschemes are more suitable for different mobility OFDM systems.Computer simulation results show that the maximal ratiocombining frequency diversity ARQ scheme and type Ⅲ HARQ with frequency diversity is more suitable for low mobilityOFDM system.However the type Ⅲ HARQ without frequency diversity is more suitable for high mobility OFDM systembecause of the remarkable time diversity which reduces the required retransmission number to about 2 at the ACPRR of0.96.     

Effects of Time-Variant WSSUS Channel on the Performance of OFDM Systems

The long symbol duration makes Orthogonal Frequency Division Multiplexing (OFDM) robust against frequency-selective fading, and also makes OFDM sensitive to time-selective fading. First, this paper deduces the Inter-subCarrier Interference (ICI) caused by time-selective fading, and then analyzes in detail how time-selective fading affects the performance of OFDM system, e.g. Bit-Error Rate (BER) and the channel capacity of each subcarrier. At last, some simulation figures are given.     

基于失配序列的OFDM信道估计

本文提出了一种利用失配序列进行OFDM信道估计的新方法。在发端将失配序列加入到OFDM信号中作为训练序列,接收端将收到的去掉循环前缀的失配序列与失配滤波器系数的循环移位序列做相关运算,利用失配序列的优良自相关特性,估计出信道的冲击响应,进而得到子载波处信道的频率响应。理论分析和仿真结果表明,该方法计算复杂度低,估计速度快、精度高,系统的BER性能好。      

一种基于用户需求的OFDM系统资源分配算法

提出了一种新的基于OFDM多用户通信系统的资源分配算法。该算法在总功率限制和用户数据率要求下,通过以下两步实现子载波、比特和功率的动态分配：第一步,基于用户的平均信道增益和数据率要求进行资源初分配（每个用户分配多少个子载波、功率）;第二步,对步骤1中的结果进行调整,最终决定每个用户分配到的子载波、功率以及比特载入方式。相比于Hujun Yjn等人提出的另一种基于用户需求的算法,新算法的基站发射功率略有增加,但复杂度大为降低,在实际运用中更有利用价值。     

基于SPW的流星余迹通信系统中的OFDM性能分析

文章介绍了OFDM关键技术，并利用SPW软件对OFDM基于FFT算法进行了仿真，同时对仿真结果进行分析。最后在不同的信道条件下，运用保护间隔和信道估计的方法对OFDM系统的误码率进行分析，并得出性能曲线。     

符号定时偏差对OFDM系统性能的影响

针对符号定时偏差对OFDM系统的影响进行了分析,推导了AWGN信道下定时偏差与信噪比损失的近似关系式,并通过仿真对分析结果进行了验证.研究表明,由于采用循环前缀,符号定时适度超前不会对系统性能造成大的影响,而定时滞后则会引入符号间干扰,使系统性能恶化.因此符号定时不一定要很精确,但一定要特别准确.