Equalising a channel using a dithered linear search algorithm adapted to change filter taps in accordance with a heuristic tap modification scheme

摘要

This invention is particularly useful for equalising communications data transmitted by optical means at a data rate of 10Gbps. A blind adaptation equaliser is disclosed. It is based on a heuristic tap modification scheme represented by the centre and right hand blocks of Figure 7. According to this scheme changes are made to initial seed values of filter taps, the changes being selected at random. The eye diagram is then measured. If the eye opening improves then the taps are changed in a similar way to the first change, if not they are changed randomly. This heuristic scheme thus employs a trial and error approach. According to the present invention the "dithered linear search" (DLS) algorithm is overlaid on top of the heuristic scheme. The DLS algorithm is represented by the left hand boxes in the figure. The DLS algorithm makes perturbations to filter taps and correlates the perturbations with a shape of an output signal from the filter. The correlations are integrated over time to produce a gradient vector which is used to calculate a magnitude and direction in which to move the filter taps. The eye opening may be measured using a mean square estimation (MSE) function.