空空高速移动通信信号的频偏估计和跟踪算法

Doppler frequency shift estimation and the tracking algorithm for air-to-air high-speed mobile communications

空空高速移动场景下飞行平台通信信号的多普勒频率范围大且变化快。针对现有频偏估计和跟踪算法难以兼顾估计精度和工程可实现性的难题,提出了低复杂度的新型高精度频偏估计和跟踪算法。首先根据空空高速移动场景下多普勒频率快速变化且具有时空相关性特征,在传统频偏模型的基础上构建适用于空空高速移动场景的时变频偏模型;然后基于此模型将相邻短前导的频偏估计值进行相互关联并处理,将频偏精度优化问题转化为经典的超定线性方程组的优化求解问题,最大限度地抑制了估计噪声,提高了频偏估计精度。仿真结果表明,该算法估计的残余频偏相对于经典算法大幅降低,当信噪比大于5 dB时,残余频偏的均方根误差控制在100 Hz范围内。针对该算法求解过程中存在的数值稳定性问题,给出了相应的工程可实现方法。该算法采用前馈补偿频偏跟踪方法,与传统的锁相环反馈跟踪方法相比,提高了系统的稳定性和时效性。

Under air-to-air high-speed mobile communications,the Doppler frequency shift of the Aerial platform has characteristics of a large range and rapid change.It is difficult for existing frequency estimation algorithms to tackle both high estimation accuracy and engineering realization feasibility.In this paper,the time-varying Doppler frequency shift model is first constructed according to the traditional frequency offset model and the spatiotemporal correlation of Doppler frequency shift versus time.Based on this model,the coarse frequency offset estimation values of adjacent short preambles are associated.The optimization problem of frequency offset estimation is transformed into a classic optimization problem of overdetermined linear equations,which reduces the estimation variance to the maximum extent and improves the estimation accuracy.Simulation results show that the residual frequency offset of the proposed algorithm is reduced significantly compared with the traditional algorithm.Simulation results show that the root mean square error(RMSE)of the proposed algorithm is less than 100 Hz when the SNR is greater than 5 dB.Aiming at the numerical stability problem existing in the proposed algorithm,the corresponding engineering realizable method is given in the paper.Unlike the traditional phase-locked loop feedback tracking scheme,the proposed algorithm adopts a feedforward compensation scheme,thereby improving the system stability and timeliness.