Blind decision feedback equalisers, how to avoid degenerative solutions (Q1853340)

Decision feedback equalisers offer a good compromise between complexity and performance for channels with strong intersymbol interference. However, their blind or decision-directed adaptation may converge to degenerative solutions for which the signal at the equaliser's output is independent of its input. The known algorithms proposed to solve this problem are evaluated in this paper. It is shown that their main defect is a lack of well-defined criteria allowing the detection of degenerative solutions, so this paper introduces a criterion proved to be sufficient for reliable detection of such solutions. Using the new criterion, an algorithm of blind decision feedback equalisation, based on constrained optimisation, is proposed. The new algorithm does not admit degenerative solutions therefore should be preferred among the analysed algorithms. Also, the problem of false phase lock, characteristic of some modulations, is addressed and a solution to it is proposed. The results of the study are presented using the experimental data and simulation.