Sequence detectors

A method for detecting symbol values corresponding to a sequence of input samples received from an ISI channel, the method comprising:

• a branch metric calculation step for calculating for each input sample, in an initial set of pipeline stages, branch metrics for respective possible transitions between states of a trellis by selecting hypothesized input values, each dependent on a possible symbol value for the input sample and L>0 previous symbol values corresponding to the respective possible transitions between states of the trellis, calculating differences between the input sample and each hypothesized input value, and comparing said differences and selecting, as the branch metric for each possible transition, an optimum difference in dependence on a predetermined state in a survivor path through the trellis;
• and
• a path metric calculation step for calculating, in a subsequent set of pipeline stages using the branch metrics from the branch metric calculation step, path metrics for respective survivor paths through the trellis by selecting said predetermined state in each survivor path in dependence on the branch metrics, said predetermined state being fed back to the branch metric calculation step,
• wherein, during the branch metric calculation step, the branch metrics are calculated in a first one or more clock periods that are different from a second one or more clock periods in which the path metrics are calculated in the path metric calculation step so as to separate a first addition operation involved in calculating the branch metrics from a second addition operation involved in calculating the path metrics and reduce a total number of addition operations on a longest path of the sequence detector.

A computer program product for detecting symbol values corresponding to a sequence of input samples received from an ISI channel, said computer program product comprising a non-transitory computer readable storage medium having program instructions embodied therein, the program instructions being executable by a processing device to cause the processing device to perform:

• a branch metric calculation step for calculating for each input sample, in an initial set of pipeline stages, branch metrics for respective possible transitions between states of a trellis by selecting hypothesized input values, each dependent on a possible symbol value for the input sample and L>0 previous symbol values corresponding to the respective possible transitions between states of the trellis, calculating differences between the input sample and each hypothesized input value, and comparing said differences and selecting, as the branch metric for each possible transition, an optimum difference in dependence on a predetermined state in a survivor path through the trellis;
• and a path metric calculation step for calculating, in a subsequent set of pipeline stages using the branch metrics from the branch metric calculation step, path metrics for respective survivor paths through the trellis by selecting said predetermined state in each survivor path in dependence on the branch metrics, said predetermined state being fed back to the branch metric calculation step,
• wherein, during the branch metric calculation step, the branch metrics are calculated in a first one or more clock periods that are different from a second one or more clock periods in which the path metrics are calculated in the path metrics calculation step so as to separate a first addition operation involved in calculating the branch metrics from a second addition operation involved in calculating the path metrics and reduce a total number of addition operations on a longest path of the sequence detector.