A new normalized block LMS based adaptive decision feedback equalizer for wireless communications

The objective of the paper is, a new normalized block LMS algorithm is developed for adaptive decision feedback equalizer (ADFE), which is suitable for high data rate wireless and mobile communication systems. Physical channels used in transmission of digital signals can be rarely represented by a nondistorting channel model with additive noise as the only impairment. In practice, the vast majority of channels are characterized by a limited bandwidth in which particular frequency components of transmitted signals are nonequally attenuated (causing amplitude distortion) and nonequally delayed (causing delay distortion). These effects are the result of the physical properties of the transmission medium and of the imperfect design of transmit and receive filters. The proposed approach exhibits better convergence characteristics to eliminate Inter symbol Interference (ISI), as compared with the conventional DFE. In this scheme the incoming data is partitioned into non overlapping blocks and the filtering operation has been performed in frequency domain with FFT(overlap and save method). In this the correction applied to the tap weight vector and it is normalized with respect to the squared euclidean norm of the tap input vector at time n. The frequency domain representation facilitates, easier to choose step size with which the proposed algorithm convergent in the mean squared sense, whereas in the time domain it requires the information on the largest eigen value of the correlation matrix of the input sequence.