一种低信噪比条件下QPSK信号盲处理方法

摘要

提出了一种用于盲估计四相编码(Quaternary phase shift key,QPSK)载波频率的改进MAT (M-MAT)算法,并给出了一种新型QPSK信号码元估计方法.在没有接收信号先验知识的情况下,首先对QPSK信号粗估计出其载频重心和3 dB带宽,并适度滤除带外噪声,之后利用MAT方法估计载频.在此基础上,利用每个码元带宽内相位幅度不变的特性,通过相邻码元的相位差值来估计码元变化.仿真结果表明,该载频估计方法估计精度高于传统的MAT方法,解码方法可以在低信噪比条件下,达到较高的解码精度.%A modified MAT (M-MAT) method for estimating the blind carrier frequency of the quaternary phase shift key (QPSK) signal is presented and a novel code estimation algorithm of the QPSK signal is proposed. Firstly, carrier frequency center and 3 dB-bandwidth of the QPSK signal are estimated coarsely without the prior knowledge of received signals, and the noise out of the bandwidth is filtered appropriately. Then, the carrier frequency can be estimated accurately by using the MAT method. Furthermore, considering the phase is constant in every code period, the code change can be estimated by analyzing the phase difference of adjacent codes. Finally, simulating results indicate that the proposed method for carrier frequency estimation is more accurate than the traditional MAT method and validate the high decoding accuracy under low signal-to-noise radio (SNR).