Patent ID: 11966587
Assignee: FUZHOU UNIVERSITY
Field: Computer technology (Electrical engineering)
Classification: CPC G  Y | IPC G

Claim 0:
1. A method for optimizing a Polar-RNNA quantizer of MLC NAND flash memory based on deep learning, comprising the following steps:
Step S1: transforming an MLC flash detection task into a deep learning task, and obtaining three hard-decision read thresholds based on a neural network;
Step S2: expanding six soft-decision read thresholds based on the three hard-decision read thresholds;
Step S3: constructing an LLR mapping table, and obtaining LLR soft information of the MLC flash based on the LLR mapping table;
Step S4: symmetrizing the MLC flash channel, and performing density evolution; and
Step S5:optimizing the soft-decision read thresholds based on a genetic algorithm to obtain optimal quantization intervals;
Step S2 specifically comprises:
obtaining the overlapping areas of two adjacent Gaussian distribution functions based on the MLC flash decoding curve;
sensing the overlapping areas with preset high quantization precision and sensing other areas with preset low quantization precision, that is, setting a difference between adjacent read thresholds of the overlapping area to be less than a difference between adjacent read thresholds of non-overlapping areas, so that a width W exits between each thresholds obtained by extension and an adjacent optimal threshold; and obtaining six extended read thresholds according to formula (2):, {
     
      
       
        
         
          B
          
           
            2
            ⁢
            i
           
           -
           1
          
          *
         
         =
         
          
           R
           i
           *
          
          -
          
           W
           
            
             2
             ⁢
             i
            
            -
            1
           
          
         
        
       
      
      
       
        
         
          B
          
           2
           ⁢
           i
          
          *
         
         =
         
          
           R
           i
           *
          
          +
          
           W
           
            2
            ⁢
            i
           
          
         
        
       
      
     
    
   
   
    
     (
     2
     )
    
   
  
 

Wherein, i=1, 2, 3, R*i ∈(B*2i-1, B*2i);
Step S3 specifically comprises: determining seven corresponding quantization intervals according to the six extended read thresholds, wherein each memory cell of MLC flash stores two bits and has four voltage stages correspondingly, a left bit is called a most significant bit and is denoted by MSB, and right bit is called a least significant bits and is denoted by LSB; and constructing the LLR mapping table, and obtaining an LLR corresponding to each bit c of a storage symbol based on the LLR mapping table;
Step S5 specifically comprises:
obtaining an optimal set {W*1, W*2, . . . , W*6} through the genetic algorithm, wherein an objective function is PB; and, {
      
       
        W
        1
        *
       
       ,
       
        W
        2
        *
       
       ,
       …
          
       ,
       
        W
        6
        *
       
      
      }
     
     =
     
      
       
        arg
        ⁢
        min
       
       
        {
        
         
          W
          1
         
         ,
         
          W
          2
         
         ,
           
         …
           
         ,
         
          W
          6
         
        
        }
       
      
      ⁢
        
      
       P
       B
      
     
    
   
   
    
     (
     5
     )
    
   
  
 

obtaining six optimal soft-decision read thresholds {B*1, B*2, . . . , B*6} according to the optimal set {W*1, W*2, . . . , W*6}, so that seven optimal quantization intervals for a Polar-code MLC flash channel are obtained.