Implementation of a blind Adaptive Decision Feedback Equalizer

This paper proposes an efficient implementation of the blind Self-Adaptive Decision Feedback Equalizer (SA-DFE) presented in [1]. This innovative low-complexity equalizer has the particularity of adjusting its structure with the difficulty of the channel. The equalizer switches to a linear recursive equalizer when the channel is very dispersive and to a decision-directed DFE when the output of the equalizer presents reliable decisions. This paper gives details about the two structures of the SA-DFE and justifies why these structures are relevant. However, this paper focuses more particularly on the transition between the two different modes of the SA-DFE. Indeed, simulations show that if the transition from one mode to another is not well-implemented, the equalizer can oscillate between the two structures involving a major loss of convergence rate. Several means to obtain smooth transitions are proposed and simulation results are presented and analyzed. This unsupervised self-adaptive equalizer has been widely tested in the case of underwater communications and shows good ability in practice to deal with severe frequency-selective and quickly time-varying channel.