单载波MPSK/MQAM调制信号的参数盲估计改进算法研究
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摘要
当对单载波多进制数字相位调制(Multiple Phase Shift Keying,MPSK)和多进制正交幅度调制(MultipleQuadrature Amplitude Modulation,MQAM)等星座类调制信号进行盲解调时,首先须进行频偏和符号速率的盲估计,传统的多次方谱频偏估计算法与二次小波符号速率估计算法具有较好的估计性能,但由于离散傅里叶变换(Discrete Fourier Transform,DFT)的栅栏效应以及噪声的影响,其估计精度和可靠性有限。针对这些问题,本文采用了新的频率估计方法从而减小栅栏效应的影响提高了频偏和符号速率的估计精度,并提出一种基于信噪比(Signal to Noise Ratio,SNR)和谱峰指数的置信度准则,增强了频偏估计的可靠性。以QPSK和16QAM为例,进行了仿真分析,仿真结果表明,改进算法复杂度略高于传统算法,但其性能优于传统算法性能,可以有效提高频偏以及符号速率的估计精度及其可靠性,16QAM和QPSK具有类似的性能趋势,但需要更高的信噪比才能达到和QPSK相同的性能。本文算法鲁棒性强,具有很好的应用价值。
Blind demodulation of constellation modulated signals such as Multiple Phase Shift Keying (MPSK) and Multiple Quadrature Amplitude Modulation (MQAM) requires blind estimation of frequency offset and symbol rate at first.The traditional estimation algorithm of frequency offset based on multiple square spectrum and estimation algorithm of the symbol rate based on quadratic wavelet have better estimation performance. However,because of the fence effect of the Discrete Fourier Transform (DFT) and the influence of noise,the accuracy and reliability of estimation are limited. To solve these problems,a new frequency offset estimation method is proposed to reduce the impact of fence effect and improve the accuracy of frequency offset estimation and symbol rate estimation. A confidence criterion based on Signal to Noise Ratio (SNR) and spectral peak index is proposed to improve the reliability of frequency offset estimation. The simulation results based on QPSK and 16QAM show that the complexity of the improved algorithm is slightly higher than that of the traditional algorithm,but its performance is better than that of the traditional algorithm. It can effectively improve the estimation accuracy and reliability of frequency offset estimation and symbol rate estimation. 16QAM and QPSK have similar performance trends,but 16QAM need higher SNR in order to achieve the same performance as QPSK. The algorithm is robust and has good application value.
Blind demodulation of constellation modulated signals such as Multiple Phase Shift Keying (MPSK) and Multiple Quadrature Amplitude Modulation (MQAM) requires blind estimation of frequency offset and symbol rate at first.The traditional estimation algorithm of frequency offset based on multiple square spectrum and estimation algorithm of the symbol rate based on quadratic wavelet have better estimation performance. However,because of the fence effect of the Discrete Fourier Transform (DFT) and the influence of noise,the accuracy and reliability of estimation are limited. To solve these problems,a new frequency offset estimation method is proposed to reduce the impact of fence effect and improve the accuracy of frequency offset estimation and symbol rate estimation. A confidence criterion based on Signal to Noise Ratio (SNR) and spectral peak index is proposed to improve the reliability of frequency offset estimation. The simulation results based on QPSK and 16QAM show that the complexity of the improved algorithm is slightly higher than that of the traditional algorithm,but its performance is better than that of the traditional algorithm. It can effectively improve the estimation accuracy and reliability of frequency offset estimation and symbol rate estimation. 16QAM and QPSK have similar performance trends,but 16QAM need higher SNR in order to achieve the same performance as QPSK. The algorithm is robust and has good application value.
引文
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[2]胡国兵,徐立中,吴珊珊,等.基于循环平稳分析的LFM信号盲处理结果可靠性评估[J].电子学报,2016,44(4):788-794.Hu Guobing,Xu Lizhong,Wu Shanshan,et al.Reliability Evaluation for Blind Processing Results of LFM Signal Based on Cyclostationarity[J].Acta Electronica Sinica,2016,44(4):788-794.(in Chinese)
[3]Proakis J G,Salehi M.Digital Communications[M].Mc Graw-Hill,2009.
[4]赵强,杨建波,刘鹏,等.一种新的联合特征调制识别算法[J].通信技术,2013,46(3):4-6,9.Zhao Qiang,Yang Jianbo,Liu Peng,et al.A New Automatic Recognition Algorithm based on Combined Feature Parameters[J].Communications Technology,2013,46(3):4-6,9.(in Chinese)
[5]孙锦华,余忠洋,段学敏.基于相位解模糊的简化对角互相关频偏估计算法[J].电子学报,2016,44(8):1974-1980.Sun Jinhua,Yu Zhongyang,Duan Xuemin.Simplified Diagonal Cross Correlation Frequency Estimation Algorithm Based on Phase Un-wrapping Method[J].Acta Electronica Sinica,2016,44(8):1974-1980.(in Chinese)
[6]金艳,田田,姬红兵.基于稀疏贝叶斯学习的码元速率估计[J].电子与信息学报,2018,40(7):79-84.Jin Yan,Tian Tian,Ji Hongbing.Symbol Rate Estimation Based on Sparse Bayesian Learning[J].Journal of Electronics and Information Technology,2018,40(7):79-84.(in Chinese)
[7]Azzouz E E,Nandi A K.Automatic Modulation Recognition of Communication Signals[J].IEEE Transactions on Communications,1997,46(4):431-436.
[8]徐毅琼.数字通信信号自动调制识别技术研究[D].解放军信息工程大学,2011.Xu Yiqiong.Research on Automatic Modulation Recognition of Digital Communication Signals[D].Information Engineering University,2011.(in Chinese)
[9]赵颖.基于改进算法的调制信号的载波频率估计[J].电子设计工程,2016,24(6):29-31.Zhao Ying.Estimation of carrier frequency of modulation signal based on improved alogorithm[J].Electronic Design Engineering,2016,24(6):29-31.(in Chinese)
[10]柏果,程郁凡,唐万斌,等.利用DFT和迭代校正的正弦信号频率估计算法[J].信号处理,2017,33(12):1536-1541.Bai Guo,Cheng Yufan,Tang Wanbin,et al.A Frequency Estimation Algorithm of Sinusoidal Signal Capable of DFTand Iterative Correction[J].Journal of Signal Processing,2017,33(12):1536-1541.(in Chinese)
[11]Yang J L,Yang W J,Xu G Q.Blind Estimation of Carrier Frequency and Symbol Rate Based on Cyclic Spectrum Density[J].Procedia Engineering,2012,29(4):514-519.
[12]Flohberger M,Kogler W,Gappmair W.Symbol Rate Estimation with Inverse Fourier Transforms[C]∥2006 International Workshop on Satellite and Space Communications,2006,110(113):14-15.
[13]纪勇,徐佩霞.基于小波变换的数字信号符号率估计[J].电路与系统学报,2003,8(1):12-15.Ji Yong,Xu Peixia.Symbol Rate Estimation of Digital Signal Based on Wavelet Transform[J].Journal of Circuits and Systems.2003,8(1):12-15.(in Chinese)
[14]张涛.基于N谱峰突出指数的典型数字调制信号盲识别研究与实现[D].成都:电子科技大学,2012.Zhang Tao.Research and Implementation of Blind Identification of Typical Digital Modulation Signals Based on NSpectral Peak Outburst Index[D].Chengdu:University of Electronic Science and Technology of China,2012.(in Chinese)
[15]Luise M,Reggiannini R.Carrier recovery in all-digital modems for burst-mode transmissions[J].IEEE Trans.Comm.,1995,43(2/3/4):1169-1178.