Blind channel-shortening for multipath channels using a recursive prediction-error filter with additional prediction delay

The prediction-error filter is a well-known tool for blind communication channel equalisation. For multipath channels, it has two disadvantages considered here. First, in transversal form, it must be substantially longer than the impulse response of the channel, with a consequent high computation cost; second, it cannot fully equalise mixed-phase channels. Here, the authors examine a recursive version of the linear predictor, used with additional prediction delay for blind channel-shortening of multipath channels with multi-carrier modulation signals using a cyclic prefix. The recursive mode of operation allows the filter length to be significantly shorter than in the transversal, non-recursive form. In tests using modelled channels, they observe two significant results. First, for channels that include maximum-phase terms, the additional prediction delay ameliorates the filter response to maximum-phase terms. Thus, channel-shortening may be achieved, at least partially, unless the maximum-phase terms are severe. Second, the recursive prediction-error filter impulse response adapts to a stable minimum-phase form. This low-cost technique, then, may be used to augment the use of a cyclic prefix in reducing inter-symbol interference in multipath channels.