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。     

一种新的综合业务多址访问方式─—多载波TDMA

一种新的综合业务多址访问方式─—多载波ＴＤＭＡ张更新（通信工程学院南京２１００１６）１引言卫星通信的多址方式可以分为ＦＤＭＡ、ＴＤＭＡ、ＳＤＭＡ和ＣＤＭＡ，而ＦＤＭＡ又可细分为ＳＣＰＣ和ＭＣＰＣ方式，ＣＤＭＡ可分为ＤＳ和ＦＨ方式，ＴＤＭＡ还包括ＡＬＯ...     

OFDM仿真软件系统研究

本文将介绍一套自行开发的适用于多种传输系统（包括ＯＦＤＭ－ＤＡＢ、ＯＦＤＭ－ＨＤＴＶ和ＯＦＤＭ－ＤＶＢ等）的ＯＦＤＭ软件仿真系统，并分析载波频偏对ＯＦＤＭ－ＤＡＢ系统和ＯＦＤＭ－ＤＶＢ－Ｔ系统的影响，以及抽样时钟误差对ＯＦＤＭ－ＤＡＢ系统的影响，最后给出相应的仿真测试结果。     

深亚微米PESD MOSFET特性研究及优化设计

本文对多晶抬高源漏（ＰＥＳＤ）ＭＯＳＦＥＴ的结构作了描述，并对深亚微米ＰＥＳＤＭＯＳ－ＦＥＴ的特性进行了模拟和研究，看到ＰＥＳＤＭＯＳＦＥＴ具有比较好的短沟道特性和亚阈值特性，其输出电流和跨导较大，且对热载流子效应的抑制能力较强，因此具有比较好的性能．给出了ＰＥＳＤＭＯＳＦＥＴ的优化设计方法．当ＭＯＳＦＥＴ尺寸缩小到深亚微米范围时，ＰＥＳＤＭＯＳ－ＦＥＴ将成为一种较为理想的器件结构     

深亚微米PESD MOSFET特性研究及优化设计

本文对多晶抬高源漏（ＰＥＳＤ）ＭＯＳＦＥＴ的结构作了描述，并对深亚微米ＰＥＳＤＭＯＳ－ＦＥＴ的特性进行了模拟和研究，看到ＰＥＳＤＭＯＳＦＥＴ具有比较好的短沟道特性和亚阈值特性，其输出电流和跨导较大，且对热载流子效应的抑制能力较强，因此具有比较好的性能．给出了ＰＥＳＤＭＯＳＦＥＴ的优化设计方法．当ＭＯＳＦＥＴ尺寸缩小到深亚微米范围时，ＰＥＳＤＭＯＳ－ＦＥＴ将成为一种较为理想的器件结构     

美国带内同频道数字音频广播（DAB）的开发状况

欧洲尤里卡１４７／ＤＡＢ方式在世界范围内推出后，很多国家正在对这种方式进行实验和开发。但是，美国广播界却另辟蹊径，他们正在开发一种不同于尤里卡１４７／ＤＡＢ的带内ＤＡＢ方式，该方式有两种：带内同频道ＤＡＢ方式（ＩＢＯＣ ＡＭ－ＤＡＢ，ＩＢＯＣ ＦＭ－ＤＡＢ）和带内邻频道ＤＡＢ方式（ＩＢＡＣ ＡＭ－ＤＡＢ，ＩＢＡＣ ＦＭ－ＤＡＢ）。本文详细介绍美国ＵＳＡ Ｄｉｇｉｔａｌ Ｒａｄｉｏ公司开发的带内同频     

有器件非线性时VSB和COFDM系统性能比较

本文对ＶＳＢ和ＣＯＦＤＭ数字传输系统的性能进行了理论分析和模拟，结果证明从线性系统角度考虑，这两种传输系统在性能上是等价的。本文还就这两种系统对器件非线性的要求进行了分析和模拟，其结果说明ＣＯＦＤＭ系统要求器件具有较小的三阶交调和三阶互调分量，并且，ＣＯＦＤＭ系统峰值－平均功率电平比较大，这将导致ＣＯＦＤＭ接收机中Ａ／Ｄ变换器和数字信号处理位数大于１２比特。     

数字声音广播的关键技术——COFDM

文章首先介绍了正交频分复用ＯＦＤＭ（ＯｒｔｈｏｇｏｎａｌＦｒｅｑｕｅｎｃｙＤｉｖｉｓｉｏｎＭｕｌｔｉｐｌｅｘｉｎｇ）的原理及其实现方法，然后介绍了数字声音广播（ＤＡＢ）的关键技术之一ＣＯＦＤＭ，最后给出了一种ＤＡＢ接收机的原理框图。     

正交频分复用码分多址技术的特点及其应用

本文分析了正交频分复用（ＯＦＤＭ）－码分多址（ＣＤＭＡ）技术的特点，介绍了几种具体的应用方案，并指出ＯＦＤＭ－ＣＤＭＡ技术是适合于高速、大容量数字移动通信系统的一种较佳技术。     

数字HDTV地面广播传输方法──第六讲 正交频分复用技术的应用

正交频分复用（ＯＦＤＭ：ＯｒｔｈｏｇｏｎａｌＦｒｅｑｕｅｎｃｙＤｉｖｉｓｉｏｎＭｕｌｔｉｐｌｅｘｉｎｇ）因其在抗多径衰落方面的优越性能，并且实现起来比较简单、频谱利用率高，得到了广泛的应用。本文介绍了ＯＦＤＭ的原理及其利用ＦＦＴ技术实现的方法，然后介绍了ＯＦＤＭ在数字化ＨＤＴＶ４面广播中的应用。     

Low‐Complexity Symbol Timing Offset Estimation Schemes for OFDM Systems

In this paper, we propose three symbol synchronization schemes for Orthogonal Frequency Division Multiplex (OFDM) systems. The cyclic extension preceding OFDM symbols is of decisive importance for these schemes. The first scheme uses the phase‐differential coding of the received OFDM signal. The second and the third schemes use the length of the received OFDM signal. All three schemes make symbol synchronization possible, even though there is a frequency offset in the system. Simulation results show that these schemes can be used to synchronize an OFDM system over AWGN and multi‐path fading channels.     

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.     

CFO estimation schemes for differential OFDM systems

This paper proposes two blind carrier frequency offset (CFO) estimation schemes for differentially modulated orthogonal frequency division multiplexing (OFDM) systems. The proposed schemes estimate the fractional part of the CFO with only two consecutive OFDM blocks, and they exploit two implicit properties associated with differentially modulated OFDM (DOFDM) systems, i.e., the channel keeps constant over two consecutive OFDM blocks, and the DOFDM systems employ an M-ary phase-shift keying constellation. One of the schemes is based on the finite alphabet (FA) constraint and the other one is based on the constant modulus (CM) constraint. They provide a trade-off between the performance and computational complexity. The constrained Cramer-Rao lower bound is also derived. Several numerical examples are presented to validate the efficacy of the proposed schemes.     

用于多媒体广播的正交频分复用模块集成系统

在０．１８μｍ工艺或更小的线宽下,可把各单个子系统有效地集成在同一块芯片上。通过讨论新工艺条件下具有语音视频图像处理功能的高速编码正效频分复用调制（ＯＦＤＭ）集成系统设计的可能方案,并剖析实例,对其离散余弦变换、快速傅里叶变换及前向纠错编码进行了分析。     

Single-block differential transmit scheme for broadband wireless MIMO-OFDM systems

In frequency-selective multiple-input multiple-output (MIMO) channel, differential space-time-frequency (DSTF) modulations are known as practical alternatives that are capable of exploiting the available spatial and frequency diversities without the requirement of multichannel estimation at the receiver. However, the encoding nature of the DSTF schemes that expand several OFDM symbol periods makes the DSTF schemes susceptible to fast-changing channel conditions. In this paper, we propose a differential scheme for MIMO-OFDM systems that is able to differentially encode signal within two OFDM symbol periods, and the proposed scheme transmits the differentially encoded signal within one OFDM block. The scheme not only reduces encoding and decoding delay but also relaxes the restriction on channel assumption. The successful differential decoding of the proposed scheme depends on the assumption that the fading channels keep constant over two OFDM symbol periods rather than multiple of them as required in the existing DSTF schemes. We also provide pairwise error probability analysis and quantify the performance criteria in terms of diversity and coding advantages. The design criteria reveal that the existing diagonal cyclic codes can be applied to achieve full diversity. Performance simulations under various channel conditions show that our proposed scheme yields superior performance to previously proposed differential schemes.     

Spectrally Precoded OFDM

By bilinearly transforming the rectangularly pulsed multicarrier basis signals, new basis sets containing full-response continuous basis signals are developed for constructing spectrally efficient orthogonal frequency-division multiplexing (OFDM) signals with or without cyclic prefix (CP) or zero padding (ZP). Both multiple-product and linear-combination formats are presented for these basis sets. In the multiple-product format, the developed full-response basis signals are shown to be zero-valued at interval edges, and thus can be used to construct continuous-phase OFDM signals. It is analytically shown that the constructed continuous-phase OFDM signals exhibit relatively small power spectral sidelobes which fall off as f^-4, and can thus provide much higher spectral efficiency than the traditional rectangularly pulsed OFDM signal. In the linear-combination format, the proposed basis signals are shown to be the linear combinations of rectangularly pulsed multicarrier basis signals, and thereby allow for the efficient realization of fast Fourier transform (FFT). Specifically, a spectrally precoded signaling structure is developed in conjunction with inverse FFT and guard insertion to construct continuous-phase OFDM signals with or without CP or ZP. The corresponding spectral decoders are also developed to enable zero-forcing (ZF) demodulation for spectrally precoded OFDM. With the zero-forcing demodulation, the spectrally precoded OFDM schemes are shown to outperform in average error-rate characteristics the conventional rectangularly pulsed and correlatively coded OFDM schemes on various delay-spread channels     

LDPC-Coded OFDM Transmission Over Graded-Index Plastic Optical Fiber Links

The possibility of 10-Gb/s transmission over graded-index plastic optical fiber (GI-POF) using the orthogonal frequency-division multiplexing (OFDM) and iteratively decodable codes is demonstrated by simulations. Several classes of low-density parity-check (LDPC) codes suitable for use in LDPC-coded OFDM transmission over GI-POF are presented as well. Several power efficient OFDM schemes are introduced     

Novel Link Adaptation Schemes for OFDM System

1　IntroductionRecently,intenseinteresthasbeenfocusedonthetransmissiontechniqueswhichcansupporthighdataratetransmissionoverwirelesschannels.OneofthemainrequirementsonthetransmissiontechniqueistheabilitytocombattheInter SymbolInterfer ence (ISI) ,amajorprobleminthehighdataratetransmissionovermultipathfadingchannels.OFDMisthemostpromisingsolutiontothisproblem[1～ 3] .ThecombinationoflinkadaptationandOFDMisaneffectivewaytoimprovethespectralefficiency[4～ 7] .TheoptimalwaytoachievetheShannon…     

Novel synchronization for TDS-OFDM-based digital television terrestrial broadcast systems

As an effective technique for combating multipath fading and for high-bit-rate transmission over wireless channels, orthogonal frequency-division multiplexing (OFDM) is extensively used in modern digital television terrestrial broadcasting (DTTB) systems to support high performance bandwidth-efficient multimedia services. In this paper, novel synchronization schemes, including timing, frequency offset estimation, and phase error tracking, are proposed for the time domain synchronous OFDM (TDS-OFDM) based DTTB systems. Simulations under different channel situations verify the efficiency of the proposed schemes.