基于IEEE80211a的OFDM基带系统的FPGA设计

摘要伴随着无线数据通信与多媒体应用的不断发展，无线传输系统对传输速率与QoS保证等方面的要求也相应地不断提高。正交频分复用（OrthogonalFrequencyDivisionMultiplexing，OFDM）作为一种新型的物理层传输技术正越来越受人们的重视，并被视为下一代移动通信（4G）中的关键技术。OFDM继承了传统MCM中多载波并行调制、符号周期相应增长的特点，在OFDM的重叠多载波技术的利用下比传统的非重叠多载波技术节省将近50%的带宽，在循环前缀的辅助下可以实现准确的符号同步，有效地将原本频率选择性衰落的信道转化为多个并行平衰落信道使用，从而OFDM技术具有频谱利用率高、抗干扰能力强等优势，大大提高了传输效率，因此该技术在新一代的通信中备受关注。IEEE802.11a无线局域网（WLAN）标准作为典型的以OFDM为物理层接入方式的应用系统，是OFDM技术的一个典型应用，本文正是以IEEE802.11a无线局域网标准为基础，对OFDM基带处理器的算法，架构进行介绍和分析的基础上，将整个系统的FPGA设计和实现分为多个基本通信模块，并给出每个模块的具体实现。采用自顶向下的FPGA设计方法，在Altera的QuartusII8.1开发环境下，采用Verilog硬件描述语言进行了长短训练序列、扰码、多速率卷积码、交织、16QAM映射、导频插入、IFFT调制、循环前缀与加窗以及主控单元等系统模块的设计;采用ModelsimSE6.5f和Matlab7.0仿真工具对设计系统进行了单元模块仿真和系统仿真,并将设计的OFDM通信发送系统下载到Altera公司的CycloneII系列EP2C8Q208C8开发板上进行了系统测试和验证，并依据系统软件仿真和硬件测试的结果进行了分析，其中重点研究分析了加窗与循环前缀对OFDM系统性能的影响。仿真和测试结果表明:基于IEEE802.11a无线局域网标准的OFDM通信发送系统符合该标准各参数要求并能够正确实现长短训练序列、扰码、多速率卷积码、交织、16QAM映射、导频插入、IFFT调制、循环前缀与加窗以及主控单元等各个模块,各个子模块系统软件仿真和整体OFDM通信发送系统测试正确,下载测试结果正确。关键词：OFDM，FPGA，IEEE802.11a，IFFT，循环前缀AbstractWithwirelessdatacommunicationandmultimediaapplicationdevelopment,therequirementsoftransferrateandQOSguaranteeneedtoimproveaccordinglyinthewirelesstransmissionsystem.OFDMasakindofnewtypeofthephysicallayertransmissiontechnologyismoreandmoregettheattentionofpeople,andbetreatedasthekeytechnologyofnextgenerationmobilecommunications(4G).OFDMinheritedthecharacteristicsofmulti-carrierparallelmodulationSymbolscyclegrowthofthetraditionalMCM.Comparedwithtraditionalnon-overlappingmulti-carriertechnology,theuseofoverlappingmulti-carrierOFDMtechnologycansavenearly50%ofthebandwidth.usingcirculationprefixcanrealizeaccuratesymbolsynchronization,changeoriginallyfrequencyselectivedeclinechannelintomultipleconcurrentflatfadingchanneleffectively.soithasagoodresistancemultipathfadingandhighspectralutilizationefficiency,greatlyimprovingthetransmissionefficiency.sothistechnologyisthehotresearchtopicinanewgenerationofcommunication.IEEE802.11wirelesslocalareanetwork(WLAN)standardasatypicalapplicationsystemofOFDMphysicallayeraccessmode,isatypicaltechnologyOFDMapplication.thepaperresearchandanalysetheOFDMbasebandprocessoralgorithmandarchitecturetomakethewholesystemFPGAdesignandimplementationdividedintoanumberofbasiccommunicationmodule,andgiveeachmoduleofthespecificimplementationbasisonwirelessLANIEEE802.11standard.Usingthetop-downdesignmethodofFPGA,intheQuartusII8.1ofAlteradevelopmentenvironment,theVeriloghardwaredescriptionlanguage(VerilogHDL)hasbeenaccomplishedtotrainingsequence,scrambler,multi-rateconvolutioncode,interweave,16QAMmapping,pilotinsertion,IFFTmodulation,cyclicprefixandwindowedandmaincontrolunitdesignofsystemmodule.ModelSimSE6.5fandMatlab7.0simulationtoolshavebeenusedtomakesystemdesignandsimulation,andaccomplishedthedesignedOFDMcommunicationtransmissionsystemtodownloadtotheFPGAhardwareplatformofCycloneIIofAlteraandfinishedthesystemtest.Besidesaccordingtotheresultofsystemsoftwaresimulationandhardwaretestmadetheanalysis,WhichfocusesontheanalysisofwidowedandcyclicforthesystemperformanceinfluenceofOFDM.Thesimulationandtestresultsshowthat:OFDMcommunicationsendsystemmeetsthestandardrequirementofthewirelesslocalareanetworkIEEE802.11standard.Suchasrainingsequence,scrambler,multi-rateconvolutioncode,interweave,16QAMmapping,pilotinsertion,IFFTmodulation,cyclicprefixandwindowedandmaincontrolunit,eachchildmodulesystemsoftwaresimulationandtheoverallOFDMcommunicationsendsystemtestright,downloadtestresultsarecorrect.KeyWords:OFDM，FPGA，IEEE802.11a，IFFT，Circulationprefix目录第1章绪论…………………………………………………………………………….11.1移动通信系统的发展概况.....................................................................................11.2IEEE802.11a标准概述…………………………………………………………..11.2.1IEEE802.11a物理层协议的参数……………………………………………...21.2.2IEEE802.11a物理层协议帧结构.......................................................................4第2章IEEE802.11a物理层的OFDM技术.................................................................72.1OFDM系统的发展状况及特点..............................................................................72.2OFDM系统的工作原理......................................................................................92.2.1OFDM系统的基本模型......................................................................................92.2.2FFT在OFDM系统中的应用...............................................................................112.3信道编码技术.......................................................................................................122.3.1扰码原理............................................................................................................122.3.2卷积码编码........................................................................................................132.3.3交织编码............................................................................................................162.4OFDM映射与调制技术.......................................................................................192.4.1映射调制.............................................................................................................192.4.2IFFT实现OFDM调制..................