【作者】 谭磊；

【导师】 陈文正； 张朝阳；

【作者基本信息】 浙江大学 ， 通信与信息系统， 2005， 硕士

【摘要】 未来通信技术和通信系统正朝着“宽带化”和“移动性”两个方向发展，以满足人们对图像、视频等高速率数据业务日益增加的业务需求，同时又在保证服务质量的前提下支持移动环境下的数据传输，如高分辨率实时图像业务、会议电视虚拟现实业务等，从而实现“任何人(Whoever)在任何地方(Wherever)任何时间(Whenever)可以同任何对方(Whomever)进行任何形式(Whatever)的通信”。OFDM(Orthogonal Frequency Division Multiplexing)技术由于具有对频率选择性和多径信道良好的抵抗能力，近年来成为了无线通信领域里的研究热点，目前业内人士普遍认为它将应用于下一代移动通信系统Beyond 3G和宽带无线接入技术中并被视为核心技术。 虽然OFDM是一种优良的宽带传输技术，但是它也存在致命的弱点，那就是它对误差比较敏感。当接收信号存在载波频偏时，如果不进行频偏补偿的话，将会直接破坏子载波间的正交性引起载波间干扰ICI(Inter-Channel Interference)；而信道传输时延、采样时钟相位和频率的偏差则会引起符号定时偏差，造成相位旋转，严重的还会引起符号间干扰ISI(Inter Symbol Interference)并进而造成ICI；另外，信号经过无线信道传输时会有衰落，如不补偿信道影响的话将会无法正确解调信号。因而，研究OFDM系统，特别是信号同步和信道估计技术具有非常重要的意义。 本文首先介绍了OFDM技术的应用背景，简要概括了OFDM技术所涉及的各种通信系统领域的发展情况。 第二章作为全文理论研究的核心内容，主要研究了接收机的信号同步。首先给出了OFDM系统理论模型，在此基础上从理论角度分析了同步误差对接收信号的影响并引出了接收机同步需要解决的问题。接着给出了物理层同步链路仿真解决方案，解析的分析了同步各环节的算法并给出了仿真曲线。 第三章阐述了OFDM系统的信道估计方法。给出了无线信道的理论模型，分析了信道对于传送信号的影响。最后介绍了OFDM信道估计方法，比较了各种方法的性能，并给出了仿真性能曲线。 第四章介绍了数字基带系统设计中数字前端设计。发送端包括整数倍零值内插、升采样滤波和升采样以及数字中频上变换，接收端包括数字下变频、整数倍抽取、降采样滤波和降采样。最后给出了数字前端仿真得到的频谱图以及用FPGA实现并用频谱分析仪测量得到的实际信号频谱图。 第五章作为全文的结束，首先介绍了OFDM基带传输系统实现的系统硬件平台，然后详细阐述了基带系统核心模块—高速定点FFT(Fast Fourier Transform)流水线处理器的FPGA(Field Programmable Gate Array)设计实现。更多还原

【Abstract】 To meet the demand of high rate datum service such as photo and video grown with days, and at the same time to support datum transmission in mobile environment such as high definition real time photo service, virtual meeting television service and so on, under prerequisite of quality of service, Two trends as "broad band" and "mobility" take on in the development of future communication techniques and systems. And the goal is to realize "Whoever, Wherever, Whenever, Whomever and Whatever communications". For the sake of good immunities to frequency selective and multi-path wireless channel, OFDM (Orthogonal Frequency Division Multiplexing) appeals to researchers in the field of wireless communication. And in this area, it’s a common sense that OFDM will be applied to next generation mobile communication system-Beyond 3G and broad band wireless access as a kernel technique.Though OFDM is an excellent broad band transmitting technique, it’s weakness is fatal, that it is sensitive to error signals. When carrier frequency offset exists in the received signal and if not compensated, the orthogonality can be broken and ICI (Inter-Channel Interference) can be introduced. And because of channel transmit delay, sample clock phase and frequency errors, symbol timing error is added, and the phases of signal are rotated. More intractably, ISI (Inter Symbol Interference) appears, which brings ICI at the same time. Also when transmitted through wireless channels, signals are attenuated, which results that signals can not be demodulated correctly. Thus research on OFDM system, especially synchronization and channel estimation techniques, is very important.At first the technique background of OFDM is introduced, and the developments of various communication systems are generalized shortly.Chapter 2 as a key part of theory research of the dissertation, mainly focuses on the synchronization of receiver. Firstly, OFDM system model is given, based on which influences of synchronization errors are analyzed in theory, then the problems are pointed out in the stage of synchronization of receiver. At last, an solution of PHY layer synchronization is proposed, and the synchronization algorithms are deduced analytically. Also the simulation figures are given.Chapter 3 studies the methods of channel estimation of OFDM system. The theory model of wireless channel is depicted, then the effect on transmit signals is illuminated. Finally, several different methods of OFDM channel estimation are introduced, performance of which are compared, and the performance compare figures are listed.Chapter 4 is about the digital front end design of base band system. In the transmitter, it includes zeros interpolation, up sample filter design, up sample and digital intermediate frequency up convert. And in the receiver, it includes digital intermediate frequency down convert, decimate, down sample filter design and down sample. At last, spectrums thatsimulated in MATLAB and measured in FPGA base band design with spectrum analyzer instrument are given.Chapter 5 as the end of the dissertation, firstly describes the hardware platform of OFDM base band system, Then fully discussed the design and implementation of the kernel system hardware module - high speed fixed-point pipeline FFT (Fast Fourier Transform) processor in FPGA (Field Programmable Gate Array) .更多还原