单载波MPSK/MQAM调制信号的参数盲估计改进算法研究

Blind Parameter Estimation Algorithm for Single-carrier MPSK/MQAM Modulation Signal

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.