基于迭代变步长LMS的数字域自干扰对消

Digital Self-Interference Cancellation Based on Iterative Variable Step-Size LMS

针对同时同频全双工(Co-frequency and Co-time Full Duplex,CCFD)系统已有的数字域干扰对消方法收敛速度慢和对消比低的问题,本文提出了迭代变步长最小均方(Least Mean Square,LMS)算法,利用该算法实现了快速收敛的高对消比数字域干扰对消.首先,改进Logistic函数,缩短其函数值由大至小的变化区间,再利用该非线性函数计算随迭代次数变化的步长因子值,从而加快干扰对消的收敛速度,高精度递推估计自干扰信道参数,即获得高的对消比.最后,理论分析了该对消方法收敛性和计算复杂度,得到了稳态条件下对消比的闭合表达式.仿真表明,该方法与已有变步长LMS对消方法相比,对消比可增加6d B以上,收敛速度可提高1倍,与最小二乘信道估计干扰对消方法相比,对消比提高了至少10d B.

Recently,the co-frequency co-time full duplex （CCFD）has been widely studied for its higher spectral ef-ficiency.However,it must avoid the strong co-channel self-interference to put this technology into practice,and the existing digital interference cancellation methods usually have slow convergence and small cancellation-ratio.Considering this obsta-cle,the digital cancellation method based on iterative variable step-size least mean square algorithm （IVSSLMS）is proposed in this paper.Firstly,the function of Logistic is modified to accelerate its tendency for value changing lower.Then,the itera-tive variable step-size is obtained through the modified nonlinear function.Consequently,convergence of interference cancel-lation is speeded up,and accurate parameters of self-interference channel are estimated to achieve high cancellation-ratio is derited.Finally,the convergence and complexity of this digital interference cancellation method are analyzed and the closed expression of steady-state cancellation-ratio is derived.Simulations verify that the cancellation-ratio of this method could a-chieve more than 6dB and 10dB in comparison with the existing variable step-size LMS methods and cancellation method based on least square channel estimation respectively,and the convergence speed could be enhanced doubled.