Method and apparatus for reduced state sequence estimation with tap-selectable decision-feedback

A receiver that receives a signal from a dispersive channel, said channel having a memory length, L, and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those (L+1) channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L+1) channel coefficients whose associated index is in the range K+1 through L are referred to as (L−K) tap-selectable coefficients, said receiver comprising:

• a channel estimator for determining the (L+1) channel coefficients associated with the (L+1) taps by analyzing a received signal;
• a tap selector for selecting V of the (L−K) tap-selectable coefficients satisfying a predetermined criteria, where V is a number of coefficients selected;
• a tap-selectable decision feedback prefilter (TS-DFP) circuit for:
• receiving (L−K) tap control signals from said tap selector;
• receiving said (L−K) tap-selectable coefficients from a channel estimator;
• receiving (L−K) symbols from the TS-RSSE which correspond to said (L−K) tap-selectable coefficients;
• and
• processing the intersymbol interference associated with L−(K+V) channel coefficients from among said (L−K) tap-selectable coefficients;
• a tap selectable reduced state sequence estimator (TS-RSSE) circuit for:
• receiving said (L−K) tap control signals and L channel coefficients from among said (L+1) channel coefficients, indexed one through L;
• processing the intersymbol interference associated with the V selected channel coefficients and K non tap-selectable channel coefficients;
• and
• selecting the best survivor path for each state of a trellis by performing an add-compare-select operation.

A receiver that receives a signal from a dispersive channel, said channel having a memory length, L, and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L−K) channel coefficients whose associated index is in the range K+1 through L are referred to as (L−K) tap-selectable coefficients, said receiver including:

• a channel estimator for determining the (L+1) channel coefficients by analyzing a received signal;
• a tap selector for selecting V channel coefficients of the (L−K) tap-selectable coefficients satisfying a predetermined criteria, where V is a number of the channel coefficients selected;
• a tap-selectable decision feedback prefilter (TS-DFP) circuit for:
• receiving, from a channel estimator, (L−K) tap control signals and L channel coefficients, indexed 1 through L, from said (L+1) channel coefficients;
• and
• reducing the intersymbol interference associated with L−(K+V) coefficients from among said (L−K) tap-selectable coefficients which were not selected by the tap selector;
• a tap selectable reduced state sequence estimator (TS-RSSE) circuit for:
• receiving said (L−K) tap control signals and L channel coefficients from among said (L+1) channel coefficients, indexed one though L;
• processing the intersymbol interference associated with the V selected channel coefficients and K non tap-selectable channel coefficients and;
• selecting the best survivor path for each state of a trellis by performing an add-compare-select operation.

A method for reducing the power consumption in a receiver that receives a signal from a dispersive channel, said channel having a memory length, L, and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L−K) channel coefficients whose associated index is in the range K+1 through L are referred to as tap-selectable coefficients, said method comprising the steps of:

• measuring a channel quality metric of a received signal;
• comparing the measured channel quality metric with a predetermined threshold to determine whether said channel quality metric is above or below said predetermined threshold;
• decreasing the number of coefficients to be processed by a tap-selectable reduced state sequence estimator (TS-RSSE) when it is determined that said channel quality metric is above said predetermined threshold, indicating a high quality channel;
• increasing the number of coefficients to be processed by said tap-selectable reduced state sequence estimator (TS-RSSE) when it is determined that said channel quality metric is below said predetermined threshold, indicating a low quality channel;
• increasing the number of coefficients to be processed by a tap-selectable decision feedback prefilter (TS-DFP) when it is determined that said channel quality metric is above said predetermined threshold, indicating a high quality channel;
• decreasing the number of coefficients to be processed by a tap-selectable decision feedback prefilter (TS-DFP) when it is determined that said channel quality metric below said predetermined threshold, indicating a low quality channel.

A method for reducing the power consumption in a receiver that receives a signal from a dispersive channel, said channel having a memory length, L, and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L−K) channel coefficients whose associated index is in the range K+1 though L are referred to as tap-selectable coefficients, said method comprising the steps of:

• measuring a channel quality metric of a received signal;
• comparing the measured channel quality metric with a predetermined threshold to determine whether said channel quality metric is above or below said predetermined threshold;
• decreasing the number of coefficients to be processed by a tap-selectable reduced state sequence estimator (TS-RSSE) when it is determined that said channel quality metric is below said predetermined threshold, indicating a high quality channel;
• increasing the number of coefficients to be processed by said tap-selectable reduced state sequence estimator (TS-RSSE) when it is determined that said channel quality metric is above said predetermined threshold, indicating a low quality channel;
• increasing the number of coefficients to be processed by a tap-selectable decision feedback prefilter (TS-DFP) when it is determined that said channel quality metric is below said predetermined threshold, indicating a high quality channel;
• decreasing the number of coefficients to be processed by a tap-selectable decision feedback prefilter(TS-DFP) when it is determined that said channel quality metric is above said predetermined threshold, indicating a low quality channel.

A method for reducing the power consumption in a receiver that receives a signal from a dispersive channel, said channel having a memory length, L, and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L−K) channel coefficients whose associated index is in the range K+1 through L are referred to as (L−K) tap-selectable coefficients, said method comprising the steps of:

• measuring a channel quality metric of a received signal;
• comparing the measured channel quality metric with a predetermined threshold to determine whether said channel quality metric is above or below said predetermined threshold;
• sorting the (L−K) tap-selectable coefficients by one of a decreasing absolute signal value and a squared value order;
• selecting either i) a number V of channel coefficients of the (L−K) tap-selectable coefficients, where the number V is less than a number of the (L−K) tap-selectable coefficients selected in a previous selection interval when it is determined that said channel quality metric is below said predetermined threshold, indicating a high quality channel;
• or
• ii) the number V of channel coefficients of the (L−K) tap-selectable coefficients, where the number V is greater than a number of the (L−K) tap-selectable coefficients selected in a previous selection interval when it is determined that said channel quality metric is above said predetermined threshold, indicating a low quality channel;
• processing intersymbol interference (ISI) associated with said V selected channel coefficients and K non-selectable channel coefficients in tap-selectable reduced state sequence estimator (TS-RSSE);
• and
• processing the ISI associated with the L−(K+V) non-selected channel coefficients in tap-selectable decision feedback prefilter (TS-DFP).

A method for reducing the power consumption in a receiver that receives a signal from a dispersive channel, said channel having a memory length, L, and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L−K) channel coefficients whose associated index is in the range K+1 through L are referred to as (L−K) tap-selectable coefficients, said method comprising the steps of:

• measuring a channel quality metric of a received signal;
• determining whether the measured channel quality metric is above or below a predetermined metric threshold;
• raising a coefficient threshold when it is determined that the measured channel quality metric is below said predetermined metric threshold, indicating a high quality channel;
• lowering said coefficient threshold when it is determined that the measured channel quality metric is above said predetermined metric threshold;
• comparing one of a squared signal value and an absolute signal value associated with (L−K) channel coefficients with said coefficient threshold to determine whether the (L−K) tap-selectable coefficients are equal to or greater than said coefficient threshold;
• processing those channel coefficients which are determined to be equal to or greater than said coefficient threshold with a higher complexity cancellation algorithm;
• and
• processing those channel coefficients which are determined to be less than said coefficient threshold with a lower complexity cancellation algorithm.

A method for processing a signal received from a dispersive channel, said channel having a memory length L and being modeled as a filter having (L+1) taps, indexed zero through L, where each of said (L+1) taps has associated therewith a channel coefficient, wherein those channel coefficients whose associated index is in the range one through K are referred to as non tap-selectable coefficients and those (L−K) channel coefficients whose associated index is in the range K+1 through L are referred to as (L−K) tap-selectable coefficients, said method comprising:

• means for estimating the (L+1) channel coefficients associated with the (L+1) taps by analyzing said received signal;
• means for selecting V channel coefficients from the (L−K) tap-selectable coefficients which satisfy a predetermined criteria, where V is a number of the channel coefficients selected;
• first processing means for processing K non tap-selectable channel coefficients and the selected V channel coefficients with a higher complexity cancellation algorithm;
• and
• second processing means for processing the L−(K+V) non-selected tap-selectable channel coefficients with a lower complexity cancellation algorithm.