Method and apparatus for reduced-state Viterbi detection in a read channel of a magnetic recording system

Abstract

A method and apparatus are disclosed for improving the maximum data rate of reduced-state Viterbi detectors with local feedback in magnetic recording systems. A read channel signal is processed in a magnetic recording device by precomputing branch metrics, intersymbol interference estimates or intersymbol interference-free signal estimates for speculative sequences of one or more channel symbols; selecting one of the precomputed values based on at least one decision from at least one corresponding state; and selecting a path having a best path metric for a given state.

1 . A method for processing a read channel signal in a magnetic recording device, said method comprising the steps of: 
 precomputing branch metrics for speculative sequences of one or more channel symbols;    selecting one of said precomputed branch metrics based on at least one decision from at least one corresponding state; and    selecting a path having a best path metric for a given state.    
     
     
         2 . The method of  claim 1 , wherein said step of selecting one of said precomputed branch metrics uses at least one pipeline register.  
     
     
         3 . The method of  claim 1 , further comprising the steps of: 
 processing a received signal using an FIR equalizer to generate an equalized received signal; and    processing said equalized received signal using a noise-predictive FIR filter to generate said signal.    
     
     
         4 . The method of  claim 3 , wherein said signal is a noise whitened signal.  
     
     
         5 . The method of  claim 3 , wherein channel coefficients used to precompute said branch metrics are a convolution of impulse responses of said FIR equalizer and said noise-predictive FIR filter.  
     
     
         6 . The method of  claim 1 , further comprising the steps of: 
 processing a received signal using an FIR equalizer to generate an equalized received signal; and    processing said equalized received signal using a plurality of noise-predictive FIR filters to generate a plurality of signals.    
     
     
         7 . The method of  claim 6 , wherein said plurality of noise-predictive FIR filters each use a corresponding set of filter coefficients.  
     
     
         8 . The method of  claim 6 , wherein said step of precomputing branch metrics uses an output of one of said plurality of noise-predictive FIR filters based on characteristics of the data.  
     
     
         9 . The method of  claim 6 , wherein a set of channel coefficients used to precompute said branch metrics is dependent on a bit pattern, and wherein said set of channel coefficients is given by a convolution of impulse responses of said FIR equalizer and one of said plurality of noise-predictive FIR filters.  
     
     
         10 . The method of  claim 1 , where said decision is an ACS decision  
     
     
         11 . The method of  claim 1 , where said decision is a survivor symbol.  
     
     
         12 . The method of  claim 1 , wherein said processing of said signal employs a trellis that includes syndrome information for a parity check code.  
     
     
         13 . A signal processor for processing a read channel signal in a magnetic recording device, comprising: 
 a branch metric unit for precomputing branch metrics for speculative sequences of one or more channel symbols;    at least one multiplexer for selecting one of said precomputed branch metrics based on at least one decision from at least one corresponding state; and    an add-compare-select unit for selecting a path having a best path metric for a given state.    
     
     
         14 . A method for processing a read channel signal in a magnetic recording device, said method comprising the steps of: 
 precomputing intersymbol interference-free signal estimates for speculative sequences of one or more channel symbols;    selecting one of said precomputed intersymbol interference-free signal estimates based on at least one decision from at least one corresponding state; and    selecting a path having a best path metric for a given state.    
     
     
         15 . The method of  claim 14 , wherein said step of selecting one of said precomputed intersymbol interference-free signal estimates uses at least one pipeline register.  
     
     
         16 . The method of  claim 14 , further comprising the steps of: 
 processing a received signal using an FIR equalizer to generate an equalized received signal; and    processing said equalized received signal using a noise-predictive FIR filter to generate said signal.    
     
     
         17 . The method of  claim 16 , wherein said signal is a noise whitened signal.  
     
     
         18 . The method of  claim 16 , wherein channel coefficients used to precompute said intersymbol interference-free signal estimates are a convolution of impulse responses of said FIR equalizer and said noise-predictive FIR filter.  
     
     
         19 . The method of  claim 14 , further comprising the steps of: 
 processing a received signal using an FIR equalizer to generate an equalized received signal; and    processing said equalized received signal using a plurality of noise-predictive FIR filters to generate a plurality of signals.    
     
     
         20 . The method of  claim 19 , wherein said plurality of noise-predictive FIR filters each use a corresponding set of filter coefficients.  
     
     
         21 . The method of  claim 19 , wherein said step of precomputing intersymbol interference-free signal estimates uses an output of one of said plurality of noise-predictive FIR filters based on characteristics of the data.  
     
     
         22 . The method of  claim 19 , wherein a set of channel coefficients used to precompute said intersymbol interference-free signal estimates is dependent on a bit pattern, and wherein said set of channel coefficients is given by a convolution of impulse responses of said FIR equalizer and one of said plurality of noise-predictive FIR filters.  
     
     
         23 . The method of  claim 14 , where said decision is an ACS decision  
     
     
         24 . The method of  claim 14 , where said decision is a survivor symbol.  
     
     
         25 . The method of  claim 14 , wherein said processing of said signal employs a trellis that includes syndrome information for a parity check code.  
     
     
         26 . A signal processor for processing a read channel signal in a magnetic recording device, comprising: 
 an intersymbol interference unit for precomputing intersymbol interference-free signal estimates for speculative sequences of one or more channel symbols;    at least one multiplexer for selecting one of said precomputed intersymbol interference-free signal estimates based on at least one decision from at least one corresponding state; and    an add-compare-select unit for selecting a path having a best path metric for a given state.    
     
     
         27 . (canceled)  
     
     
         28 . (canceled)  
     
     
         29 . (canceled)  
     
     
         30 . (canceled)