Qpsk If Digital Receiver Synchronization Algorithm

Along with the rapid development of digital signal processing technology and Large Scale Integrated circuit (LSI),the theory, method and technology of digital receiver receive more and more recognition. In the process of signal digital intermediate-frequency received, digital down convertion, frequency tracking of carrier and phase locked loop are the keys.This paper investigated several key problems of synchronization method of QPSK intermediate frequency digital received. First of all, modulation and digital intermediate frequency reception of QPSK signal were introduced, in particular of how to change the intermediate frequency signal down to baseband. In seccession, the algorithm of carrier frequency and phase tracking were detailed researched. In the part of frequency tracking, algorithm and performance of maximum likelihood estimation and cross-product automatic frequency control were mostly analysed. By comparing some performance of two methods, cross-product automatic frequency control was choosed to tracking the carrier frequency. In part of tracking carrier phase, algorithm and loop performance of traditional costas loop, maximum likelihood estimation of phase and clock, and Hilbert transform method were introduced. After comparing their advantages and disadvantages, costas loop was choosed at last to track carrier phase. At last, clock estimation as an absolutely necessarily part was introduced.In this paper, every algorithm was analysed, and the performance was emulated in Matlab. After comparing on the base of emulational result, the process of digital intermediate frequency receiver for QPSK signal was finally determined.