Methods and apparatus for improved threshold adaptation for a euclidean detector

Abstract

Improved threshold adaptation is provided for a predefined pattern in data. A detection threshold employed by a Euclidean detector to detect a pattern (such as a Servo Address Mark) in data is adapted by determining a minimum Euclidean distance metric D p before the pattern is declared in a given portion of the data; determining a Euclidean distance metric D s at a time when the pattern is found in the given portion, wherein at least one of the patterns is found using a Hamming detector; determining, for a plurality of the portions, a minimum D p value, D pmin , that is a substantial minimum D p value for the plurality of portions and a maximum D s value, D smax , that is a substantial maximum D s value for the plurality of portions; and determining the detection threshold based on the minimum D p value, D pmin , and the maximum D s value, D smax . The detection threshold is optionally based on a configurable margin gain value.

We claim: 
     
         1 . A method for adapting a detection threshold employed by a Euclidean detector to detect a pattern in data, comprising:
 determining a substantially minimum Euclidean distance metric D p  before said pattern is declared in a given portion of said data;   determining a Euclidean distance metric D s  at a time when said pattern is found in said given portion, wherein at least one of said patterns is found using a Hamming detector;   determining, for a plurality of said portions, a minimum D p  value, D pmin , that is a substantial minimum D p  value for said plurality of portions and a maximum D s  value, D smax , that is a substantial maximum D s  value for said plurality of portions; and   determining said detection threshold based on said minimum D p  value, D pmin , and said maximum D s  value, D smax .   
     
     
         2 . The method of  claim 1 , wherein said pattern comprises one or more of a Servo Address Mark (SAM), a Repeatable Run Out data (RRO) Address Mark (RROAM), an image pattern and an antenna signal pattern. 
     
     
         3 . The method of  claim 1 , wherein said pattern comprises one or more of a Servo Address Mark (SAM) and wherein said portion comprises a given servo sector of a disk and said plurality of said portions comprises said disk. 
     
     
         4 . The method of  claim 1 , wherein said detection threshold D thr  is computed as follows:
     D   thr   =D   smax   +g   m ×( D   pmin   −D   smax )
   
       where g m  is a margin gain value. 
     
     
         5 . The method of  claim 4 , wherein said margin gain value, g m , may be selected from the values consisting essentially of ⅛, ¼, ½ and ¾. 
     
     
         6 . The method of  claim 4 , wherein said margin gain value, gm, is a configurable value. 
     
     
         7 . The method of  claim 1 , wherein said Euclidean distance metric is computed as follows: 
       
         
           
             
               
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         8 . The method of  claim 1 , further comprising the step of detecting said pattern if said Euclidean distance metric between soft metrics of a received code word and ideal soft metrics of said pattern is less than or equal to said detection threshold. 
     
     
         9 . A tangible machine-readable recordable storage medium for adapting a detection threshold employed by a Euclidean detector to detect a pattern in data, wherein one or more software programs when executed by one or more processing devices implement the steps of the method of  claim 1 . 
     
     
         10 . An apparatus for adapting a detection threshold employed by a Euclidean detector to detect a pattern in data, comprising:
 a memory; and   at least one hardware device, coupled to the memory, operative to:   determine a substantially minimum Euclidean distance metric D p  before said pattern is declared in a given portion of said data;   determine a Euclidean distance metric D s  at a time when said pattern is found in said given portion, wherein at least one of said patterns is found using a Hamming detector;   determine, for a plurality of said portions, a minimum D p  value, D pmin , that is a substantial minimum D p  value for said plurality of portions and a maximum D s  value, D smax , that is a substantial maximum D s  value for said plurality of portions; and determine said detection threshold based on said minimum D p  value, D pmin , and said maximum D s  value, D smax .   
     
     
         11 . The apparatus of  claim 10 , wherein said pattern comprises one or more of a Servo Address Mark (SAM), a Repeatable Run Out data (RRO) Address Mark (RROAM), an image pattern and an antenna signal pattern. 
     
     
         12 . The apparatus of  claim 10 , wherein said pattern comprises one or more of a Servo Address Mark (SAM) and wherein said portion comprises a given servo sector of a disk and said plurality of said portions comprises said disk. 
     
     
         13 . The apparatus of  claim 10 , wherein said detection threshold D thr  is computed as follows:
     D   thr   =D   smax   +g   m ×( D   pmin   −D   smax )
   
       where g m  is a margin gain value. 
     
     
         14 . The apparatus of  claim 13 , wherein said margin gain value, g m , is a configurable value. 
     
     
         15 . The apparatus of  claim 10 , wherein said at least one hardware device is further configured to detect said pattern if said Euclidean distance metric between soft metrics of a received code word and ideal soft metrics of said pattern is less than or equal to said detection threshold. 
     
     
         16 . An apparatus for adapting a detection threshold for a pattern in data, comprising:
 a Euclidean detector to determine, for each of a plurality of portions of said data, (i) a substantially minimum Euclidean distance metric D p  before said pattern is declared in a given portion of said data and (ii) a Euclidean distance metric D s  at a time when said pattern is found in said given portion of said data;   a Hamming detector to detect at least one of said patterns;   a comparator to determine, for a plurality of said portions, a minimum D p  value, D pmin , that is a substantial minimum D p  value for said plurality of portions and a maximum D s  value, D smax , that is a substantial maximum D s  value for said plurality of portions; and   a threshold calculator to determine said detection threshold based on said minimum D p  value, D pmin , and said maximum D s  value, D smax .   
     
     
         17 . The apparatus of  claim 16 , wherein said pattern comprises one or more of a Servo Address Mark (SAM), a Repeatable Run Out data (RRO) Address Mark (RROAM), an image pattern and an antenna signal pattern. 
     
     
         18 . The apparatus of  claim 16 , wherein said pattern comprises one or more of a Servo Address Mark (SAM) and wherein said portion comprises a given servo sector of a disk and said plurality of said portions comprises said disk. 
     
     
         19 . The apparatus of  claim 16 , wherein said detection threshold is based on a configurable margin gain value. 
     
     
         20 . The apparatus of  claim 16 , wherein said pattern is detected if said Euclidean distance metric between soft metrics of a received code word and ideal soft metrics of said pattern is less than or equal to said detection threshold.