OFDM技术标准化展望

本文主要介绍了OFDM的原理和技术优势,分析了现存的几种类型的OFDM技术特点,最后展望了OFDM标准化和在第四代移动通信系统的应用.     

Odd clipping optical orthogonal frequency division multiplexing for VLC system

The Orthogonal Frequency Division Multiplexing (OFDM) has emerged as one of the promising techniques because of its robustness to multipath fading with high‐speed data transmission. Classical bipolar OFDM cannot be used in intensity modulated with direct detection (IM/DD) optical communication systems, as visible light communication (VLC), so many optical modulation techniques as asymmetrical clipped optical OFDM (ACO‐OFDM) and DC‐Clipped OFDM (DCO‐OFDM) have been investigated. In this paper, we introduce a novel optical modulation scheme that meets the optical communications requirements. The proposed odd clipping optical OFDM technique (OCO‐OFDM) is based on the Fourier transform symmetry properties in which the imaginary and odd signal is converted to odd and real valued signal. As a result of this work, the proposed OCO‐OFDM and its modified version have several benefits over ACO‐OFDM and DCO‐OFDM. By introducing a better bit error rate, with the same spectral efficiency as DCO‐OFDM and the same power efficiency as ACO‐OFDM for real valued modulation technique as Binary Phase‐Shift Keying (BPSK), and with the same spectral efficiency and power efficiency as ACO‐OFDM for complex valued modulation technique as Quadrature Phase‐Shift Keying (QPSK) and Eight Phase‐Shift Keying (8PSK).     

小波提升变换OFDM系统抗脉冲性能分析

利用小波提升理论构造一种新的多载波(OFDM)系统,在原傅里叶变换的OFDM(FFT-OFDM)系统的优越性的基础上,扩大系统容量及有效地利用系统的带宽,并使整个系统简单化.进一步对小波提升变换OFDM及傅里叶变换OFDM的抗脉冲干扰性能进行了深入研究,仿真与实验结果表明:基于小波提升的OFDM系统抗脉冲干扰特性远远优于传统OFDM系统.     

Performance analysis of broadband satellite communication system based on OFDM/TDM

Orthogonal frequency division multiplexing （OFDM） is attracting more attention for its capability of high speed transmission. However, the OFDM possesses an obvious shortage in its high ratio of the peak power to the average power （PAPR）, which has become the main issue holding it back to be applied to the broadband satellite communication system. OFDM combined with time division multiplexing （TDM）, dividing the subcarriers of OFDM into some blocks in time tune, can decrease the high PAPR of OFDM. Meanwhile, the advantages of OFDM can be preserved. In this paper, OFDM/TDM is applied to the broadband satellite communication system. This paper theoretically analyses OFDM/TDM system model as well as its restraining effect on PAPR, and proposes frequency domain multiplexing-pilot （FDM-Pilot） channel estimation algorithm. Simulation results show OFDM/TDM in broadband satellite communication system has approving performance and decreased the PAPR.     

PAPR Reduction in OFDM Systems with Large Number of Sub-Carriers by Carrier Interferometry Approaches

High Peak-to-Average Power Ratio(PAPR)is one of the major drawbacks of Orthogonal Frequency DivisionMultiplexing(OFDM)systems.This paper presents the structures of the particular bit sequences leading to the maximumPAPR(PAPR_(max))in Carrier-Interferometry OFDM(CI/OFDM)and Pseudo Orthogonal Carrier-Interferometry OFDM(PO-CI/OFDM)systems for Binary Phase Shift Keying(BPSK)modulation.Furthermore,the simulation and analysisof PAPR_(max) and PAPR cumulative distribution in CI/OFDM and PO-CI/OFDM systems with 2048 sub-carriers are pre-sented in this paper.The results show that the PAPR of OFDM system with large number of sub-carriers reduced evidentlyvia CI approaches.     

OFDM SAR成像方法综述

近年来,正交频分复用(OFDM)信号由于具有正交性以及大带宽特性被广泛应用于合成孔径成像(SAR)研究中。相比传统SAR成像,由于其信号的独特性,OFDM SAR在成像上具有一定优势,但也面临着很多挑战。该文根据天线配置的不同,分别对单天线OFDM SAR成像和多天线MIMO OFDM SAR成像所面临的问题进行了梳理与总结,重点讨论了基于OFDM信号和基于循环前缀(CP)OFDM信号的SAR/MIMO SAR成像方法,并分析了OFDM SAR未来的可能发展方向。      

ZP-CI/OFDM: A Power Efficient Wireless Transmission Technology

Low power efficiency is a deficiency in traditional Orthogonal Frequency Division Multiplexing (OFDM) systems. To counter this problem, a new wireless transmission technology based on Zero-Padding Carrier Interferometry OFDM (ZP-CI/OFDM) is proposed. In a ZP-CI/OFDM system, transmission symbols are spread to all OFDM subcarriers via carrier interferometry codes. This reduces the Peak-to-Average Power Ratio (PAPR) that traditional OFDM suffers and also exploits frequency diversity gain. By zero-padding at the transmitter, advanced receiver technologies can be adopted for ZP-CI/OFDM so that frequency diversity gain can be further utilized and the power efficiency of the system is improved.     

自适应OFDM系统的仿真研究

OFDM（正交频分复用）是一种无线环境下的高速传输技术,适合在多径传播和多普勒频移的无线移动信道中传输高速数据.他能有效对抗多径效应,消除符号间干扰,对抗频率选择性衰落,而且信道利用率高.本文介绍了OFDM技术特点,讨论了自适应OFDM系统,并运用Matlab/Simulnk软件,对自适应OFDM系统进行了仿真.通过仿真结果的对比得出结论,在相同的信道信噪比（SNR）下,自适应的OFDM系统比传统的OFDM系统有更低的误比特率（BER）.     

无线OFDM系统同步技术综述

近年来,正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）技术得到了非常广泛的应用,而同步性能的好坏对于采用OFDM技术的系统能否正常工作有很大的影响。文章介绍了OFDM系统的一般同步流程,对几种经典的OFDM系统同步算法进行了综述,并分析了OFDM系统同步技术的发展方向。     

基于复小波包的OFDM调制方法(CWP-OFDM)的研究

目前,基于DFT变换的OFDM高效调制方法(DFT-OFDM)已经成为无线传输领域中的重要研究热点.但是,为达到较高的业务质量,DFT-OFDM采用了插入循环前缀(CP)的办法以减少ISI,从而降低了频谱利用率.为进一步改善频谱的利用效率,本文提出一种基于复小波包(Complex Wavelet Packet)正/反变换的OFDM调制方法(CWP-OFDM),并且将其与DFT-OFDM进行比较.仿真结果表明,在GSM TU50 信道环境中,当具有更高频谱效率的情况下,CWP-OFDM可以具有与DFT-OFDM同样或更好的误码性能.     

OFDM技术在4G中的应用

首先给出了正交频分复用(OFDM)技术的概念,详细叙述OFDM技术的基本原理和研究现状,阐述OFDM的关键技术及在4G中的应用,给出了4G的技术规范、技术要求和国内外对4G中关键技术的研究现状。分析表明OFDM技术在不增加带宽的情况下能提高系统容量,是4G移动通信技术中的核心技术。最后给出OFDM在今后的4G移动通信系统中的研究方向。     

基于循环自相关的OFDM时间参数盲估计改进算法研究

在非协作通信领域，传统的基于循环自相关的OFDM（Orthogonal Frequency Division Multiplexing，正交频分复用）时间参数盲估计算法常分析的是无导频OFDM信号，不适用于实际应用场景中含导频OFDM信号的参数盲估计。本文分析了不同导频图案的OFDM信号循环自相关谱特性，针对谱特征变化改进了OFDM信号参数估计算法。改进算法既适用于无导频OFDM信号，也适用于不同导频图案的OFDM信号。仿真结果表明，对于无导频OFDM信号，改进算法比传统算法的时间参数估计误差可降低一个数量级；同时改进算法有效避免了导频引入的二阶周期性谱峰对OFDM时间参数估计的影响，可精确估计含导频OFDM信号的时间参数，具有很好的鲁棒性和应用价值。      

无线OFDM技术

本文首先介绍了正交频分复用技术（OFDM）的原理，技术优点，它在无线局域网中的应用特点，然后分析了在宽带无线接入技术中，三种基于OFDM的高速无线传输技术；VOFDM、WOFDM和flash-OFDM的性能特点，最后展望了OFDM在未来移动通信系统中的应用。     

Parallel Channel Estimator and Equalizer for Mobile OFDM Systems

Mobile OFDM refers to OFDM systems with fast moving transceivers, in contrast to traditional OFDM systems whose transceivers are stationary or have a low velocity. In this paper, we use the basis expansion model (BEM) to model time-varying OFDM channels. Using different BEM’s, we investigate various architectures to implement the least-squares (LS) channel estimation and its corresponding zero-forcing (ZF) channel equalization. The experimental results show that our implementation for mobile OFDM systems is capable of combatting the time variation of mobile OFDM channels, and more hardware resource utilization is necessary compared with a traditional OFDM design which fails in a time-varying scenario. For mobile OFDM systems, different BEM’s are available for the channel modeling. We observe that the so-called Critically sampled Complex-Exponential BEM (CCE-BEM) leads to the most efficient hardware architecture while still maintaining high modeling accuracy.     

Improvement and Analysis of Carrier-Interferometry Orthogonal Frequency Division Multiplexing System

1IntroductionOrthogonal Frequency Division Multiplexing(OFDM) isknown to be with high spectrumefficiency and effectivein coping with such wireless channel i mpairments asmultipath fading and Inter-Symbol Interference(ISI)[1]. Moreover ,OFDMsystems have become prac-tical toi mplement using Fast Fourier Transform(FFT)techniques[2]thanks to advances in digital signal pro-cessing. Up to the present , OFDMhas been employedin several digital transmission systems , such as AD-SL[3], HIP…     

光频分复用（OFDM）技术及应用

本文叙述了光频分复用（ＯＦＤＭ）技术的特点，ＯＦＤＭ传输系统的组成及工作原理，扼要地分析了几个关键部件对ＯＦＤＭ传输系统的影响，介绍了ＯＦＤＭ系统中的光器件的主要类型及特性。最后介绍了光频分复用技术在各种通信网中的几种应用。     

OFDM系统的扩频性能分析

提出传统OFDM系统中隐藏着类似扩频系统的性质。通过减少系统使用的子载波数,揭示了OFDM系统的扩频特性。使用扩频系统的理论分析方法,分析了OFDM系统的扩频性能。OFDM系统具有与传统扩频系统类似的扩频性能,因此可以采用OFDM系统构建扩频系统。     

High-throughput, high-performance OFDM via pseudo-orthogonal carrier interferometry spreading codes

The paper introduces to orthogonal frequency-division multiplexing (OFDM) systems a novel pseudo-orthogonal carrier interferometry spreading code which spreads each parallel data stream over all the OFDM carriers. Pseudo-orthogonal carrier interferometry (PO-CI) spreading codes are carefully selected to introduce the following benefits to OFDM: up to 2N parallel data streams can be coded onto N carriers, with little degradation in performance; when rate 1/2 channel coding is applied in addition to PO-CI spreading codes, the resulting binary phase-shift keying OFDM systems demonstrate the performance of coded OFDM and the throughput of uncoded OFDM; PO-CI codes are carefully selected to spread in a manner which eliminates the peak-to-average power ratio problems characteristic of traditional OFDM.     

一种OFDM系统中PAPR的抑制算法

为降低正交频分复用(OFDM)系统中发射信号的峰值功率,提出了在一个OFDM符号内使用两种信号星座图对二进制数据进行编码,通过在各个子载波处选用合理的信号星座图来实现对峰值均值功率比(PAPR)的抑制。由于算法不改变现有OFDM系统的实现结构,在不影响OFDM中其它信号处理性能的条件下,仿真表明算法能有效地降低系统的峰值均值功率比。     

多载波CDMA系统仿真与性能分析

多载波CDMA是OFDM和CDMA结合的综合技术,兼有OFDM和CDMA的优点,可以在无线信道中传送高速数据流,在频谱效率、频率分集、抗多径干扰等方面都能获得较大好处。首先介绍了OFDM的基本原理,给出MC-CDMA的系统模型,然后通过仿真,比较了OFDM系统和MC-CDMA系统的误码性能。结果表明,MC-CDMA系统性能优于OFDM系统,说明了OFDM和CDMA技术结合的必要性。