A COMBINED FAST ADAPTIVE FILTER ALGORITHM WITH AN AUTOMATIC SWITCHINGMETHOD

This paper proposes a new combined fast algorithm for transversal adap tive fitters. The fast transversal filter (FTF) algorithm and the norm alized LMS (NLMS) are combined in the following way. In the initializa tion period, the FTF is used to obtain fast convergence. After converg ing, the algorithm is switched to the NLMS algorithm because the FTF c annot be used for a long time due to its numerical instability. Nonsta tionary environment, that is, time varying unknown system for instance , is classified into three categories: slow time varying, fast time va rying and sudden time varying systems. The NLMS algorithm is applied t o the first situation. In the latter two cases, however, the NLMS algo rithm cannot provide a good performance. So, the FTF algorithm is sele cted. Switching between the two algorithms is automatically controlled by using the difference of the MSE sequence. If the difference exceed s a threshold, then the FTF is selected. Other wise, the NLMS is selec ted. Compared with the RLS algorithm, the proposed combined algorithm needs less computation, while maintaining the same performance. Furthe rmore, compared with the FTF algorithm, it provides numerically stable operation.