基于IEEE 802.11a的OFDM传输系统的算法研究与部分硬件实现

【作者】 老元威；

【导师】 仇佩亮；

【作者基本信息】 浙江大学 ， 通信与信息系统， 2003， 硕士

【摘要】 目前，以互联网业务为代表的网络应用，正快速地向包括数据、语音、图像的综合宽带多媒体方向发展，构建宽带化、大容量、全业务、智能化的现代通信网络已成为大势所趋。宽带无线接入凭借其组网快速灵活、运营维护方便及成本较低等竞争优势，迅速成为市场热点。宽带无线接入技术的发展极为迅速：各种微波、无线通信领域的先进手段和方法不断引入，各种宽带固定无线接入技术迅速涌现，包括3.5GHz频段中宽带无线接入系统、26GHz频段LMDS系统和无线局域网WLAN等。 无线局域网常常被看作为有线网络和用户端计算机之间的“最后一公里”链路，从IEEE在1997年批准第一个无线局域网标准IEEE 802.11规范开始，这项技术正在不断发展。而IEEE802.11a物理层协议规范中采用的OFDM传输技术，由于其先天的对抗多径信道衰落的特性，越来越多受到重视，而成为当今宽带无线通信领域发展的热点。本文既是在此背景下，在IEEE 802.11a协议规范内，对基于分组的OFDM突发传输系统的进行了研究，重点对于OFDM传输中关键问题之一的信号同步进行了较为详细的分析和比较，提出了可行性算法和部分模块的硬件实现。 第一章介绍了宽带无线接入技术的发展，比较了当要的主要实现方式。在考察了无线信道特性之后，提出了OFDM技术应用的特点，并对OFDM技术的基本原理给出了说明。 第二章给出了IEEE 802.11协议的概述，着重介绍了IEEE 802.11a的物理层技术规范，即基于分组的突发传输模式的OFDM帧的组成。 第三章是全文的主体部分，在建立适合无线局域网传输信道的系统模型的基础上，定量的分析了各种参数对于接收信号的影响，并由此对于OFDM传输中的帧同步、定时同步、载波同步等关键问题进行了重点研究，提出了适合硬件实现的同步算法，包括捕获和跟踪环路的设计；同时对于信道估计和非线性补偿等问题也进行了一定的分析。最后对于相关理论做了补充说明，为后续的工作做好了铺垫。 第四章在第三章对各个算法模块研究的基础上，提出了适合IEEE 802.11a的OFDM数字接收机的系统方案，并建立了系统仿真平台，得到了一些初步的系统仿真结果。同时，介绍了OFDM基带传输平台的硬件实现，对于OFDM数字接收机中一些关键模块也给出了硬件实现说明。更多还原

【Abstract】 Nowadays, the wide application of networks, for instance, Internet, is developing fast in the direction of integrated broadband multimedia, which consists of data, voice, image and so on. Broadband Wireless Access (BWA) technology has become a hot spot of the market because of its many advantages. All kinds of advanced technology in microwave and wireless communications are introduced to BWA. During recent years many kinds of BWA technology are coming out, which mainly consists of 3.5 GHz BWA systems, 26GHz LMDS systems and Wireless Local Area Networks (WLAN).WLAN is generally considered as the ’last mile’ in the connection of computers and wired networks. In 1997, IEEE started to frame and to approve WLAN standards, IEEE 802.11. And Orthogonal Frequency Division Multiplexing (OFDM) in IEEE 802.1 la is given more and more attention because of its various advantages in lessening the severe effects of frequency selective fading. This thesis presents the studies of the physical layer of IEEE 802.11 a, which is a packet-based OFDM transmission system. It gives feasible algorithms, and primary implementation of some key modules are discussed as well.Chapter I gives a brief survey of the development of Broadband Wireless Access. After an introduction of the characteristics of wireless access channels, we give out the application traits of OFDM and its basic principles.Chapter II studies the general content of IEEE 802.11 protocol, focusing on the Physical Layer Specifications of IEEE 802.11 a, which tells how the packet-based OFDM frame is composed and formed in burst transmission mode.Chapter III, as the kernel part of the thesis, constructs a system model taking consideration of WLAN fading channels at the very beginning. The quantitative analysis of channel parameter errors to received signals is derived then, and we pay special attention to key modules in OFDM transmission and advance hardware-realizable algorithms, such as Frame Synchronization, Timing Synchronization and Carrier Synchronization. Channel estimation and nonlinear compensation are also discussed. Relative theories of DPLL and Interpolation Filters are added in the end.Chapter IV advances two kinds of proposed systematic schemes of OFDM digital receivers in accordance with IEEE 802.1 la on the basis of the algorithms analysis in Chapter III. The system simulation model is constructed here, and some primary results are achieved. At the same time, it introduces the hardware implementation of an OFDM baseband transmission platform. Implementation of some key modules in OFDM digital receiver is studied as well.更多还原