DETECTING CODEWORDS IN SOLID-STATE STORAGE DEVICES

• US 20130086457A1
• Filed: 09/19/2012
• Published: 04/04/2013
• Est. Priority Date: 09/29/2011
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Mittelholzer, Thomas, Papandreou, Nikolaos, Pozidis, Charalampos
• Granted Patent: US 8,930,803 B2
• Time in Patent Office: Days
• US Class Current: 714/806
• CPC Class Codes: G11C 11/5678 using amorphous/crystalline phase transition storage elements
• CPC Class Codes: G11C 2211/563 Multilevel memory reading aspects
• CPC Class Codes: G11C 2211/5634 Reference cells

Abstract

A method for detecting codewords in solid-state storage devices. The method includes the steps of: obtaining respective read signals by reading memory cells that stores a group of codewords, where each of the read signals includes N signal components corresponding to respective symbols of the codeword; producing an ordered read signal by ordering the components of each of the read signals according to a signal level; producing an average read signal by averaging corresponding components of the ordered read signals; determining a reference signal level that corresponds to each of q levels of the memory cells in relation to the average read signal with predefined probabilities of each symbol value occurring at each symbol position in the codeword, where the symbols of the codeword are ordered according to the symbol value; and detecting the codeword corresponding to each of the read signal in relation to the reference signal levels.

Claims

1. A method for detecting codewords in solid-state storage devices, the method comprising the steps of:

obtaining, by a processor of the computer system, respective read signals by reading memory cells that stores a group of N-symbol codewords, wherein each of said read signals comprises N signal components corresponding to respective symbols of said codeword;

producing, by the processor, an ordered read signal by ordering said components of each of said read signals according to a signal level;

producing, by the processor, an average read signal by averaging corresponding components of said ordered read signals;

determining, by the processor, a reference signal level that corresponds to each of q levels of said memory cells in relation to said average read signal with predefined probabilities of each symbol value occurring at each symbol position in said codeword, wherein said symbols of said codeword are ordered according to said symbol value; and

detecting, by the processor, said codeword corresponding to each of said read signal in relation to said reference signal levels;

wherein each of said codewords is a permutation of an N-symbol vector in a predefined set of said N-symbol vectors;

wherein each of said symbols of each said codeword has one of q symbol values; and

wherein said symbols are stored in respective q-level cells of solid state memory, where N≧

q>

2.

2. The method according to claim 1, wherein:

said symbols of said vector are ordered according to said symbol value; and

said probabilities are related to said symbol values at each of said symbol position in said set of vectors.

3. The method according to claim 2, wherein:

said set of said vectors comprises a plurality of said vectors; and

said probabilities are dependent on the number of valid codewords that are permutations of each said vector.

4. The method according to claim 3, further comprising the steps of:

defining a set of linear equations for said reference signal levels in relation to said average read signal and said predefined probabilities; and

solving said set of linear equations to determine said reference signal levels.

5. The method according to claim 4, further comprising the step of:

solving said set of linear equations by using a least-squares method.

6. The method according to claim 3, wherein said step of detecting said codeword corresponding to each of said read signal further comprises the steps of:

producing a vector signal corresponding to each said vector by replacing each symbol of said vector with said reference signal level that corresponds to said symbol value; and

identifying said vector by determining which vector signal is closest to said ordered read signal for said codeword.

7. The method according to claim 6, further comprising the step of:

detecting each of said codeword by applying an inverse permutation to said vector identified for said codeword, wherein said inverse permutation is an inverse of said permutation of said read signal producing said ordered read signal for said codeword.

8. The method according to claim 6, further comprising the steps of:

calculating statistical data for a distribution of said read signal component levels corresponding to each of said q levels of said memory cells from said ordered read signals and said vectors identified for said codewords corresponding thereto; and

identifying said vector in relation to said ordered read signal for said codeword and said statistical data.

9. The method according to claim 8, wherein said vectors are identified in relation to said statistical data by using one of a maximum-a-posteriori detection method and a maximum-likelihood detection method.

10. The method according to claim 8, further comprising the steps of:

detecting each of said codeword by applying an inverse permutation to vector identified; and

using said statistical data for said codeword,

wherein said inverse permutation is an inverse of said permutation of said read signal producing said ordered read signal for said codeword.

11. The method according to claim 1, wherein said N-symbol codewords are codewords of a translation stable code.

12. The method according to claim 1, wherein said group of codewords are read substantially simultaneously.

13. The method according to claim 1, wherein said group of said codewords comprises codewords written substantially simultaneously to said solid state memory.

14. An apparatus for detecting solid state storage devices, the apparatus comprising:

a memory controller configured to obtain read signals by reading memory cells that store a group of codewords, wherein each of said read signal comprises N signal components corresponding to said symbols of said codeword; and

a codeword detector configured to;

produce an ordered read signal by ordering said components of each of said read signals according to a signal level;

produce an average read signal by averaging corresponding components of said ordered read signals;

determine a reference signal level that corresponds to each of q levels of said memory cells in relation to said average read signal with predefined probabilities of each symbol value occurring at each symbol position in said codeword, wherein said symbols of said codeword are ordered according to said symbol value; and

detect said codeword corresponding to each of said read signal in relation to said reference signal levels;

wherein each of said codewords is a permutation of an N-symbol vector in a predefined set of said N-symbol vectors;

wherein each of said symbols of each said codeword has one of q symbol values; and

wherein said symbols are stored in respective q-level cells of solid state memory, where N≧

q>

2.

15. A solid-state storage device, comprising:

a solid-state memory having q-level cells, wherein q>

2;

a writing apparatus for writing N-symbol codewords in said solid-state memory where N≧

q;

wherein each of said N-symbol codewords is a permutation of an N-symbol vector of a predefined set of said N-symbol vectors;

wherein said each of said symbols of each said codeword has one of q symbol values; and

wherein said symbols are stored in respective q-level cells; and

a codeword detector configured to;

produce an ordered read signal by ordering said components of each of said read signals according to a signal level;

produce an average read signal by averaging corresponding components of said ordered read signals;

determine a reference signal level that corresponds to each of q levels of said memory cells in relation to said average read signal with predefined probabilities of each symbol value occurring at each symbol position in said codeword, wherein said symbols of said codeword are ordered according to said symbol value; and

detect said codeword corresponding to each of said read signal in relation to said reference signal levels.