Efficient reduced state maximum likelihood sequence estimator

A modem comprising:

• a partial response class V (PRV) equalizer coupled in a receive path of the modem;
• a reduced state maximum likelihood sequence estimator (MLSE) coupled to the PRV equalizer;
• and
• wherein the MLSE further comprises:
• a plurality kn of retained states, each of the retained states having an associated state metric, kn being less than a total number of possible states;
• a set of (J)(kn) new states, determined according to J transitions, J being a less than a size of a symbol alphabet, and an associated set of new state metrics;
• and
• a threshold for comparison to the new state metrics.

A modem comprising a reduced state maximum likelihood sequence estimator (MLSE) in a receive path of the modem wherein the reduced state maximum likelihood sequence estimator further maintains storage encoding:

• a plurality kn of retained states, each of the retained states having an associated state metric, kn being less than a total number of possible states;
• a set of (J)(kn) new states, determined according to J transitions, J being a less than a size of a symbol alphabet, and an associated set of new state metrics;
• and
• a threshold for comparison to the new state metrics.

A method of operating a modem comprising:

• generating a partial response using an equalizer on a received signal, the equalizer having a partial response class V (PRV);
• providing the output of the PRV equalizer to a reduced state maximum likelihood sequence estimator;
• and
• generating an estimate of the transmitted symbol using a variable number of reduced states and the received signal, wherein the variable number of the reduced states is determined as a function of a metric of one of the reduced states and an associated transition metric.

A method of operating a modem comprising:

• generating a partial response using an equalizer on a received signal, the equalizer having a partial response class V (PRV);
• providing the output of the PRV equalizer to a reduced state maximum likelihood sequence estimator;
• and
• generating an estimate of the transmitted symbol using a variable number of reduced states and the received signal, wherein the variable number of reduced states is determined according to an adaptively determined threshold.

A method of operating a modem comprising:

• providing a most likely estimate of a transmitted symbol using a reduced state maximum likelihood sequence estimator;
• generating an estimate of the transmitted symbol using a variable number of reduced states in the maximum likelihood sequence estimator;
• and
• determining the variable number of reduced states according to an empirically determined metric threshold, wherein the empirically determined metric threshold is empirically determined according to a previous number of previously retained states.

A method of implementing a reduced state maximum likelihood sequence detector comprising:

• retaining a varying number of states, the number of retained states being determined according to an adaptive threshold;
• and
• determining the number of retained states by comparing the metrics of potential retained states to the adaptive threshold,
• wherein the adaptive threshold is adaptive according to the previous number of previously retained states.

A method of decoding a received signal, comprising:

• retaining a first plurality of retained states, the first plurality being less than a number of possible states;
• dynamically determining a threshold for comparison with state metrics;
• determining a second plurality of new states and associated state metrics;
• and
• keeping as new retained states those new states having a metric less than the dynamically determined threshold.

A computer program product implementing a reduced state maximum likelihood sequence estimator for a received signal encoded in a machine readable medium and executable on a computer to:

• retain kn states of a total number of K states, kn<K, each retained state having an associated state metric;
• determine (J)(kn) new states based on kn previous states and a most recently received sample, using J transitions, J being a less than L, where L is a size of a symbol alphabet;
• determine (J)(kn) new state metrics associated respectively with each new state;
• perform a comparison of the new state metrics to a threshold;
• and
• keep as new retained states those states whose metric does not exceed the threshold.

A communication device comprising:

• a reduced state maximum likelihood sequence estimator coupled into a received path of the communication device;
• retained state storage;
• and
• means for selecting new states to be retained in the retained state storage based on a dynamically calculated state metric threshold, wherein the dynamically calculated state metric threshold is dynamically calculated according to a previous number of previously retained states.