脉冲噪声下基于分数低阶矩的MQAM信号载频与符号率联合估计

针对传统MQAM信号载频与符号率估计算法在脉冲噪声下性能不佳甚至失效的问题，该文结合分数低阶矩与共变理论，推导了MQAM的分数低阶循环谱密度函数，并分析了升余弦脉冲成型条件下的MQAM信号循环谱特征。将分数低阶矩引入离散频域平滑谱(DFSM)估计。提出了一种基于分数低阶矩的MQAM载波频率与符号率联合参数估计算法，采用相邻谱切面求平均的方法，有效的避免了由于分辨率不足造成估计误差。仿真实验结果表明，与二阶DFSM循环谱估计算法相比，本文算法不仅能够抑制脉冲噪声的影响，而且在较为恶劣的噪声条件下均能有效的估计MQAM信号的载频与符号率，具有更好的抗干扰能力与适用性，适用于不同调制阶数的MQAM信号。 

Joint Estimation of Carrier Frequency and Symbol Rate of MQAM signal Based on Fractional Lower Order Moments under Impulsive Noise

In view of the poor performance and even failure of the traditional MQAM signal carrier frequency and symbol rate estimation algorithm under impulse noise. By combining the fractional lower order moment(FLOM) and covariant theory, he fractional lower order cyclic spectral density function of the MQAM is derived in this paper, and the characteristics of signal cyclic spectrum under raised cosine pulse shaping are analyzed. Then, a joint carrier frequency and symbol rate estimation algorithm of MQAM based on FLOM is proposed by introducing the FLOM into discrete frequency domain smoothing method(DFSM). And the method of averaging by adjacent spectral section is used here to avoid the estimation error caused by the lack of resolution. The simulation results show that compared with the second-order DFSM cyclic spectrum estimation algorithm, the proposed algorithm can not only suppress the impulse noise, but also can effectively estimate the carrier frequency and symbol rate of the MQAM signal in the harsh noise conditions, and have better anti-interference ability and application. It is suitable for MQAM signals with different modulation orders.