基于IEEE 802.11a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（Orthogonal Frequency Division Multiplexing，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Quartus II8.1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Modelsim SE6.5f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Cyclone II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，IEEE 802.11a，IFFT，循环前缀AbstractWith wireless data communication and multimedia application development, the requirements of transfer rate and QOS guarantee need to improve accordingly in the wireless transmission system. OFDM as a kind of new type of the physical layer transmission technology is more and more get the attention of people, and be treated as the key technology of next generation mobile communications (4 G). OFDM inherited the characteristics of multi-carrier parallel modulation Symbols cycle growth of the traditional MCM. Compared with traditional non-overlapping multi-carrier technology, the use of overlapping multi-carrier OFDM technology can save nearly 50% of the bandwidth. using circulation prefix can realize accurate symbol synchronization, change originally frequency selective decline channel into multiple concurrent flat fading channel effectively. so it has a good resistance multipath fading and high spectral utilization efficiency, greatly improving the transmission efficiency. so this technology is the hot research topic in a new generation of communication.IEEE802.11 wireless local area network (WLAN) standard as a typical application system of OFDM physical layer access mode, is a typical technology OFDM application. the paper research and analyse the OFDM baseband processor algorithm and architecture to make the whole system FPGA design and implementation divided into a number of basic communication module, and give each module of the specific implementation basis on wireless LAN IEEE802.11 standard. Using the top-down design method of FPGA, in the Quartus II8.1 of Altera development environment, the Verilog hardware description language (Verilog HDL) has been accomplished to training sequence, scrambler, multi-rate convolution code, interweave, 16QAM mapping, pilot insertion, IFFT modulation, cyclic prefix and windowed and main control unit design of system module. ModelSim SE 6.5f and Matlab7.0 simulation tools have been used to make system design and simulation, and accomplished the designed OFDM communication transmission system to download to the FPGA hardware platform of Cyclone II of Altera and finished the system test. Besides according to the result of system software simulation and hardware test made the analysis, Which focuses on the analysis of widowed and cyclic for the system performance influence of OFDM.The simulation and test results show that: OFDM communication send system meets thestandard requirement of the wireless local area network IEEE802.11 standard. Such as raining sequence, scrambler, multi-rate convolution code, interweave, 16QAM mapping, pilot insertion, IFFT modulation, cyclic prefix and windowed and main control unit, each child module system software simulation and the overall OFDM communication send system test right, download test results are correct.Key Words: OFDM，FPGA，IEEE 802.11a，IFFT，Circulation prefix目录第1章绪论 (1)1.1移动通信系统的发展概况 (1)1.2 IEEE 802.11a标准概述 (1)1.2.1 IEEE 802.11a物理层协议的参数 (2)1.2.2 IEEE 802.11a物理层协议帧结构 (4)第2章IEEE 802.11a物理层的OFDM技术 (7)2.1 OFDM系统的发展状况及特点 (7)2.2 OFDM系统的工作原理 (9)2.2.1 OFDM系统的基本模型 (9)2.2.2 FFT在OFDM系统中的应用 (11)2.3 信道编码技术 (12)2.3.1 扰码原理 (12)2.3.2 卷积码编码 (13)2.3.3 交织编码 (16)2.4 OFDM映射与调制技术 (19)2.4.1映射调制 (19)2.4.2 IFFT实现OFDM调制 (22)2.5 循环前缀与加窗技术 (24)2.5.1 循环前缀 (24)2.5.2 加窗 (26)2.6 OFDM的同步信号 (27)2.6.1符号同步简介 (27)2.6.2 导频插入 (28)2.6.3训练序列的生成 (29)第3章基于IEEE 802.11a的OFDM基带系统的FPGA设计 (32)3.1 IEEE 802.11a基带处理器的发射端总体方案设计 (33)3.2基带处理器的工作时钟 (35)3.2.1 工作时钟分析 (35)3.2.2 工作时钟生成模块的实现 (36)3.3基带数据处理单元设计 (37)3.3.1 扰码器模块的实现 (37)3.3.2 多码速卷积码硬件结构与实现 (39)3.3.3 802.11a中的交织器的实现 (44)3.4 OFDM前导序列设计 (49)3.4.1 训练序列生成模块的实现 (49)3.5 映射与OFDM子载波调制 (55)3.5.1 16QAM映射模块的实现 (55)3.5.2 子载波（IFFT）调制模块 (57)3.5.3 导频插入模块的实现 (61)3.6循环前缀与加窗模块的实现 (65)3.7主控模块设计 (67)第4章系统测试与结果仿真 (71)4.1系统时钟单元测试 (71)4.2基带数据处理单元仿真测试 (71)4.2.1并串转换模块测试 (71)4.2.2 扰码模块的测试 (72)4.2.3 多码率卷积编码模块测试 (72)4.2.4 交织模块测试 (72)4.3前导序列单元仿真测试 (73)4.3.1短训练序列模块测试 (73)4.3.2长训练序列模块测试 (73)4.4映射与调制单元仿真测试 (74)4.4.1 16QAM映射模块测试 (74)4.4.2 导频插入模块测试 (75)4.4.3 IFFT调制模块测试 (77)4.5 循环前缀仿真测试 (77)4.6 主控模块测试 (78)4.7 OFPM发送系统整体仿真测试 (78)结论 (80)参考文献 (81)附录 (82)致谢 (83)第1章绪论1.1移动通信系统的发展概况移动通信越来越广泛地渗透到人们的日常生活和经济生活中, 并成为世界各国最主要的高新技术支柱产业之一同时人们对移动通信的各种需求与日俱增, 也推动了移动通信的飞速发展。