文档介绍：基于FPGA的CDMA数字基带收发系统
——调制部分
内容提要:
CDMA( Code Division Multiple Access )即码分多址接入技术,具有很强的抗干扰能力(信号隐蔽,抑制窄带干扰等)和保密性,地址改变也比较灵活。我们在了解现代通信技术的发展、CDMA基本原理以及CDMA系统的工作过程的基础上,运用MAX+plusⅡ软件,通过编程在FPGA中实现了CDMA数字基带收发系统中的4路信息信号的扩频、编码调制。系统首先将模数(A/D)转换器转换的4路数字信号通过Walsh码调制、PN码扩频、基带求和以及并串转换后得到基带信号,接收端通过相反的过程,解调出原数据信号,再通过数模(D/A)转换器,还原出原模拟信号。
本文给出了CDMA数字基带收发系统的软硬件设计方案。并以Altera MAX+plusⅡ为硬件开发平台,利用FPGA实现了4路信息信号的扩频、编码调制。
关键词:FPGA Walsh码调制 PN码扩频基带求和并串转换
Digital Base-band System of CDMA Based on FPGA
—Modulation Part
Abstract:CDMA (Code Division Multiple Access) has very strong ability of anti-jamming (signal covert, suppresses selective interference and so on) and keeping secrecy. It’s address changing is quite easy. Based on understanding the development of munication, the basic principle of CDMA and the work process of system, we utilize the MAX+plusⅡsoftware, realize 4 groups information signal’s widening frequency, the coding modulation and the demodulation by programming. In the CDMA numeral base band receiving and dispatching system, the dispatching system transforms 4 digital signals which have been switched by analog-digital (A/D) switch-box through the Walsh code modulation, the PN code spectrum-spread, the base band summation and the serial transformation at first, then the receiving part adopts the opposite process, demodulates 4 digital signals, gains the prime digital signals. The prime digital signals passes the digital-analog (D/A) switch-box, returns to the original simulated signals in the end.
This article has produced the design proposal of the CDMA numeral base band receiving and dispatching system. And take Altera MAX+plusⅡ as the platform of the hardware development. The system realizes the widening frequency, the coding modulation and the demodulation of 4 groups information signal by FPGA.
Key words: FPGA the Walsh code modulation PN code spectrum-spread the base band summation the serial transformation.
目录
一、概述 1
二、CDMA基本原理 1
(一)引理 1
(二)码分多址基本概念 2
(三)沃尔什码