基于滑窗滤波和多项式拟合的时变信道估计方法

基于长期演进（LTE）的车辆到一切（LTE-V2X）标准沿用LTE标准的帧格式，并采用块状导频辅助的单载波频分多址（SC-FDMA）系统完成信道估计。然而，由于V2X信道的时变特性，接收机信道估计面对巨大的技术挑战。因此，设计了一种基于滑窗滤波和多项式拟合的时变信道估计方法。针对导频符号处的噪声问题，在最小二乘（LS）方法基础上，采用了自适应长度的滑动窗口滤波进行降噪处理，从而保证导频符号处的信道估计精度。另外，根据多普勒频移大小，设计了自适应阶次的多项式拟合方法来跟踪数据符号处的信道变化。仿真结果表明，所提方法在LS方法的基础上有良好的去噪效果，在低速移动情况下的估计精度介于LS方法和线性最小均方误差（LMMSE）方法之间，而该方法在高速移动条件下能更好地拟合信道的时变特性，且性能上超过了LMMSE方法结合线性插值的信道估计方法。以上结果说明，所提方法相对于对比方法具有更好的自适应性，适用于不同的信道噪声和终端移动速度下的LTE-V2X通信场景。

Time-varying channel estimation method based on sliding window filtering and polynomial fitting

The Long Term Evolution based Vehicle to Everything (LTE-V2X) standard follows the LTE standard's frame format and uses a block-type pilot assisted Single-Carrier Frequency-Division Multiple Access (SC-FDMA) system for channel estimation. However, due to the time-varying characteristics of the V2X channel, large technical challenges are brought to the channel estimation at the receiver. Therefore, a time-varying channel estimation method based on sliding window filtering and polynomial fitting was designed. Aiming at the noise problem at pilot symbols, based on Least Squares (LS) method, an adaptive-length sliding window filtering was adopted for noise reduction, so as to ensure the channel estimation accuracy of pilot symbols. Furthermore, according to the size of the Doppler frequency shift of data symbols, an adaptive-order polynomial fitting method was designed to track the channel changes at data symbols. The simulation results show that the proposed method has a good denoising effect based on LS method. In the case of low-speed movement, the estimation accuracy of the proposed method is between those of LS method and Linear Minimum Mean Square Error (LMMSE) method. In the case of high-speed movement, the proposed method can fit the time-varying channel characteristics better, and its performance exceeds that of the channel estimation method of LMMSE method combined with linear interpolation. The above results show that the proposed method has better adaptability than the comparison methods and is suitable for LTE-V2X communication scenarios with different channel noises and terminal moving speeds.