# US 8,976,904 B2 · Automated erasure slicer threshold control and modification of symbol estimates to be erased > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,976,904 B2 - Document ID: US8976904B2 - Status: Granted - Kind: B2 - Application number: 13/631,229 - Filed: 2012-09-28 - Published: 2014-04-03 - Granted: 2015-03-10 - Earliest claimed: 2012-09-28 - Assignees: Intel Corporation - Applicants: Intel Corporation - Inventors: Noam Tal - Web page: https://patentgrep.com/patent/US8976904B2 ## CPC - H04L 25/0307: {using blind adaptation} - H04L 25/063: {Setting decision thresholds using feedback techniques only} - H04L 2025/0342: {QAM} - H04L 2025/03694: {Stop and go} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Methods and systems to vary an erasure slicer threshold based on a measure computed from prior soft and/or hard symbol decisions, identify reliable symbol estimates based on the threshold, identify unreliable symbol estimates for erasure based on the threshold, modify the identified symbol estimates, output the reliable symbol estimates and the modified symbol estimates as erasure slicer decisions, and filter the decisions in a feedback filter of a decision feedback equalizer (DFE). The erasure slicer threshold may be based on signal-to-noise ratio (SNR) or mean-squared-error (MSE). A symbol estimate may be identified for erasure when a coordinate of the corresponding soft decision is within an erasure area defined by the threshold. Symbol modification may include replacing a corresponding coordinate of the symbol estimate with a coordinate of a decision boundary associated with the erasure area. ## Claims ### Claim 1 An apparatus, comprising: a soft decision system to determine soft decisions for symbols of a signal as coordinates within a quadrature amplitude modulated (QAM) constellation; a hard decision system to determine hard decisions for the symbols as points within the QAM constellation based on the soft decisions; an erasure slicer to evaluate the soft decisions based on a threshold distance, including to determine if a coordinate of a soft decision falls within the threshold distance of a boundary between points of the QAM constellation; and a threshold module to vary the threshold distance based on variations in a difference between the soft decisions and the hard decisions; wherein the soft decision system is configured to determine the soft decisions based on samples of the QAM signal and an output of the erasure slicer. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the threshold module is configured to maintain an average of the difference between the soft decisions and the hard decisions over a sliding window of symbols of the signal, and vary the threshold distance based on variations in the average. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the threshold module is configured to determine the difference between the soft decisions and the hard decisions as a signal-to-noise ratio between the soft decisions and the hard decisions, and vary the threshold distance based on variations in the signal-to-noise ratio. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the threshold module is configured to vary the threshold distance based on a mean squared error between the soft decisions and the hard decisions, and vary the threshold distance based on variations in the mean squared error. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein the threshold module is configured to: weight the difference between the soft decisions and the hard decisions for each symbol within a sliding window of symbols of the signal based on a weighting factor; maintain an average of the weighted differences over the sliding window of symbols; and vary the threshold distance based on variations in the average; wherein the threshold module is configurable with respect to the weight factor to vary a sensitivity of the threshold distance relative to a frequency of variations in the difference between the soft decisions and the hard decisions. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the threshold module is configured to: maintain an average of the difference between the soft decisions and the hard decisions over a sliding window of symbols of the signal; and compute the threshold distance as 1 minus the average. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the erasure slicer is configured to modify the coordinate of the soft decision if the soft decision falls within the variable threshold distance of the boundary. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein the erasure slicer is further configured to change the coordinate of the soft decision to the boundary between the points of the QAM constellation if the soft decision falls within the variable threshold distance of the boundary. ### Claim 9 A non-transitory computer readable medium encoded with a computer program, including instructions to cause a processor to: determine soft decisions for symbols of a signal as coordinates within a quadrature amplitude modulated (QAM) constellation; determine hard decisions for the symbols as points within the QAM constellation based on the soft decisions; evaluate the soft decisions based on a threshold distance, including to determine if a coordinate of a soft decision falls within the threshold distance of a boundary between points of a QAM constellation; vary the threshold distance based on variations in a difference between the soft decisions and the hard decisions; and determine the soft decisions based on samples of the QAM signal and results of the evaluation of the soft decisions. ### Claim 10 (depends on 9) The computer readable medium of claim 9, further including instructions to cause the processor to maintain an average of the difference between the soft decisions and the hard decisions over a sliding window of the symbols of signal, and vary the threshold distance based on variations in the average. ### Claim 11 (depends on 9) The computer readable medium of claim 9, further including instructions to cause the processor to determine the difference between the soft decisions and the hard decisions as a signal-to-noise ratio between the soft decisions and the hard decisions of the symbols, and vary the threshold distance based on variations in the signal-to-noise ratio. ### Claim 12 (depends on 9) The computer readable medium of claim 9, further including instructions to cause the processor to vary the threshold distance based on a mean squared error between the soft decisions and the hard decisions, and vary the threshold distance based on variations in the mean squared error. ### Claim 13 (depends on 9) The computer readable medium of claim 9, further including instructions to cause the processor to; weight the difference between the soft decisions and the hard decisions for each symbol within a sliding window of symbols of the signal based on a weighting factor; maintain an average of the weighted differences over the sliding window of symbols; vary the threshold distance based on variations in the average; and adjust the weight factor to vary a sensitivity of the threshold distance relative to a frequency of variations in the difference between the soft decisions and the hard decisions. ### Claim 14 (depends on 9) The computer readable medium of claim 9, further including instructions to cause the processor to; maintain an average of the difference between the soft decisions and the hard decisions over a sliding window of symbols of the signal; and compute the threshold distance as 1 minus the average. ### Claim 15 (depends on 9) The computer readable medium of claim 9, further including instructions to cause the processor to modify the coordinate of the soft decision if the soft decision falls within the variable threshold distance of the boundary. ### Claim 16 (depends on 15) The computer readable medium of claim 15, further including instructions to cause the processor to change the coordinate of the soft decision to the boundary between the points of the QAM constellation if the soft decision falls within the variable threshold distance of the boundary. ### Claim 17 A method, comprising: determining soft decisions for symbols of a signal as coordinates within a quadrature amplitude modulated (QAM) constellation; determining hard decisions for the symbols as points within the QAM constellation based on the soft decisions; evaluating the soft decisions based on a threshold distance, including determining if a coordinate of a soft decision falls within the threshold distance of a boundary between points of a QAM constellation; and varying the threshold distance based on variations in a difference between the soft decisions and the hard decisions wherein the determining soft decisions includes determining the soft decisions based on samples of the QAM signal and results of the evaluation of the soft decisions. ### Claim 18 (depends on 17) The method of claim 17, wherein the varying the threshold distance includes maintaining an average of the difference between the soft decisions and the hard decisions, and varying the threshold distance based on variations in the average. ### Claim 19 (depends on 17) The method of claim 17, wherein the varying the threshold distance includes determining the difference between the soft decisions and the hard decisions as a signal-to-noise ratio of the symbols, and varying the threshold distance based on variations in the signal-to-noise ratio. ### Claim 20 (depends on 17) The method of claim 17, wherein the varying the threshold distance includes varying the threshold distance based on a mean squared error between the soft decisions and corresponding hard decisions, and varying the threshold distance based on variations in the mean squared error. ### Claim 21 (depends on 17) The method of claim 17, wherein the varying the threshold distance includes: weighting the difference between the soft decisions and the hard decisions for each symbol within a sliding window of symbols of the signal based on a weighting factor; maintaining an average of the weighted differences over the sliding window of symbols; varying the threshold distance based on variations in the average; and adjusting the weight factor to vary a sensitivity of the threshold distance relative to a frequency of variations in the difference between the soft decisions and the hard decisions. ### Claim 22 (depends on 17) The method of claim 17, wherein the varying the threshold distance includes: maintaining an average of the difference between the soft decisions and the hard decisions over a sliding window of symbols of the signal; and computing the threshold distance as 1 minus the average. ### Claim 23 (depends on 17) The method of claim 17, further including modifying the coordinate of the soft decision if the soft decision falls within the variable threshold distance of the boundary. ### Claim 24 (depends on 23) The method of claim 23, wherein the modifying includes changing the coordinate of the soft decision to the boundary between the points of the QAM constellation if the soft decision falls within the variable threshold distance of the boundary. ### Claim 25 A system, comprising a processor and memory, a user interface system, and a communication system to interface between a communication network and one or more of the processor and the user interface system, wherein the communication system includes: a soft decision system to determine soft decisions for symbols of a received signal as coordinates within a quadrature amplitude modulated (QAM) constellation; a hard decision system to determine hard decisions for the symbols as points within the QAM constellation based on the soft decisions; an erasure slicer to evaluate the soft decisions based on a threshold distance, including to determine if a coordinate of a soft decision falls within the threshold distance of a boundary between points of the QAM constellation and a threshold module to vary the threshold distance based on variations in a difference between the soft decisions and the hard decisions; wherein the soft decision system is configured to determine the soft decisions based on samples of the QAM signal and an output of the erasure slicer. ### Claim 26 (depends on 25) The system of claim 25, wherein the threshold module is configured to vary the threshold distance based on a mean squared error (MSE) between the soft decisions and corresponding hard decisions, and vary the threshold distance based on variations in the mean squared error. ### Claim 27 (depends on 25) The system of claim 25, wherein the erasure slicer is configured to modify the coordinate of the soft decision if the soft decision falls within the variable threshold distance of the boundary. ### Claim 28 (depends on 27) The system of claim 27, wherein the erasure slicer is further configured to change the coordinate of the soft decision to the boundary between the points of the QAM constellation if the soft decision falls within the variable threshold distance of the boundary.