大学生本科毕业设计
（论文）
题目：PI/4-QPSK信号的调制与解调
专业 电子与通信工程 类别 计算机模拟 日期 05年5月
摘 要
在以前的数字蜂窝系统中，往往采用FSK、ASK、PSK等调制方式。随着数字蜂窝系统的发展，对调制和数字蜂窝系统的技术要求越来越高, 许多优秀的调制技术应运而生，其中PI/4-QPSK技术是无线通信中比较突出的一种二进制调制方法。
本文首先介绍了数字相位调制的一般原理；然后对PI/4-QPSK的调制原理进行了阐述，并对影响调制性能的滤波器进行了分析与研究；最后重点研究了PI/4-QPSK的三种解调方法并通过用Matlab对这一过程进行编程，得出信号在不同信噪比下模拟传输的时域图、频域图及功率谱密度曲线等，并在相同信道条件下通过眼图和误码率曲线图对PI/4-QPSK的三种解调方法进行了性能比较，得出了基带差分解调性能最差、中频差分解调性能次之、鉴频器解调性能最优的结论。
关键词 PI/4-QPSK；同相信道；正交信道；调制；差分解调
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Abstract
Previous digital honeycomb system often adopt modulation way of FSK, ASK, PSK etc. Along with development of digital honeycomb system the tec- hnical criterion of modulation and demodulation will be adjusted to meet hig- her requirement. A lot of excellent modulation technology has emerged as the times require, the PI/4-QPSK is one of the most outstanding technology in radio communication.
This paper introduces the modem theory and process of the digital phase modulation first.Then studied the detection method of PI/4-QPSK and analyzed the filter which can influence the system’s performance. Finally, the process of three demodulate methods of the PI/4-QPSK was emulated .It also addresses a method for programming with Matlab to analyze the PI/4-QPSK system and descry bees how to emulate the system separately via ideal signal channel and interfered channels with different signal to noise ratio. The article analyses the dynamic and static behaviors of the PI/4-QPSK system as well as the performance against noise under the condition of Gauss noise channe1.The comparison is made on the eye pattern and curve of bit error rate between PI/4-DQPSK’s three demodulate methods under the same channel. The result of simulation shows that the performance of the baseband differential detector is less than the IF-band differential detector’s, the performance of the FM-discriminator detector is the best.
Keywords PI/4-QPSK, In-phase channel, Quadrature channel, Modulation, Differential demodulation
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目 录
摘 要 ............................................................................................................. I Abstract .......................................................................................................II 第1章 绪论 ...............................................................................................1 1.1 课题背景...........................................................................................1 1.2 PI/4-QPSK研究现状 .......................................................................1 1.3 PI/4-QPSK信号的产生和定义 .......................................................2 1.4 PI/4-QPSK的优点 ...........................................................................3 1.5 本文主要研究内容和具体工作.......................................................3 第2章 数字相位调制概述及性能比较...................................................5 2.1 数字相位调制概述...........................................................................5 2.1.1 四相QPSK的一般原理.............................................................5 2.1.2 偏移QPSK的一般原理.............................................................6 2.1.3 PI/4-QPSK的一般原理...............................................................8 2.2 PI/4-QPSK与QPSK、OQPSK的性能比较 ..................................8 2.3 PI/4-QPSK与GMSK的性能比较 ..................................................9 2.4 本章小结.........................................................................................10 第3章 PI/4-QPSK的调制 .................................................................... 11 3.1 PI/4-QPSK调制原理 ..................................................................... 11 3.1.1 PI/4-QPSK信号的产生............................................................. 11 3.1.2 PI/4-QPSK的调制原理............................................................. 11 3.2 PI/4-QPSK调制过程中滤波器的选取与研究 .............................15 3.2.1 PI/4-QPSK调制方式下噪声与干扰的分析.............................15 3.2.2 滤波器的设计与选择 ...............................................................16 3.3 本章小结.........................................................................................17 第四章 PI/4-QPSK的解调 ....................................................................18
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