Method and apparatus for encoding and decoding digital communications data
In one aspect, the present invention is a system and technique that provides for the systematic development or implementation of codes that increase the robustness of systems employing, for example, PAM-n transmission techniques. The system and technique of this aspect of the invention eliminate, minimize, reduce or limit transitions between extreme signaling levels. As a result, the slew rate employed and/or required by the transmitter may reduce crosstalk and intersymbol interference, and provide for wider “eye” openings from the perspective of the receiver.
1. A method of encoding a first n-bit data word for transmission in a communications system, the communications system including a transmitter, a receiver, a communications channel and a first subset of n-bit data words, wherein each data word of the first subset is assigned a unique subset of one or more coded data words, the method comprising:
determining a second n-bit data word, of the first subset of n-bit data words, that corresponds to the first n-bit data word;
selecting a first coded data word, from a unique subset of coded data words associated with the second n-bit data word;
providing the first coded data word for transmission over the communications channel as one or more multi-level symbols;
wherein a code space, formed by combining each unique subset of coded data words associated with each data word of the first subset of n-bit data words, excludes any coded data word that has a transition from a maximum value symbol to a minimum value symbol and excludes any coded data word that has a transition from the minimum value symbol to the maximum value symbol; and
wherein the first coded data word is selected to minimize an absolute value of an RDS, unless a selection would produce a transition, with respect to a boundary symbol of another coded data word, that is between a maximum level and a minimum level.
2. The method according to claim 1 , wherein the code space excludes all coded data words having a maximum value symbol as a boundary symbol.
3. The method according to claim 1 , wherein the code space excludes all coded data words having a minimum value symbol as a boundary symbol.
4. The method according to claim 1 , wherein a unique subset, for an n-bit data word of the first subset of n-bit data words, is assigned a coded data word having a maximum value symbol as a boundary symbol and a coded word having a non-maximum value symbol as a boundary symbol.
5. The method according to claim 1 wherein a unique subset, for an n-bit data word of the first subset of n-bit data words, is assigned a coded data word having a minimum value symbol as a boundary symbol and a coded word having a non-minimum value symbol as a boundary symbol.
6. The method of claim 1 , further comprising:
scrambling the first n-bit data word, prior to using the first n-bit data word to determine the second n-bit data word.
7. The method of claim 1 , wherein each unique subset with a plurality of coded data words has at least two coded data words with different weights.
8. A system for encoding a first n-bit data word for transmission in a communications system, the communications system including a transmitter, a receiver, a communications channel and a first subset of n-bit data words, wherein each data word of the first subset is assigned a unique subset of one or more coded data words, the method comprising:
a subsystem configured for determining a second n-bit data word, of the first subset of n-bit data words, that corresponds to the first n-bit data word;
a subsystem configured for selecting a first coded data word, from a unique subset of coded data words associated with the second n-bit data word;
a subsystem configured for providing the first coded data word for transmission over the communications channel as one or more multi-level symbols;
wherein a code space, formed by combining each unique subset of coded data words associated with each data word of the first subset of n-bit data words, excludes any coded data word that has a transition from a maximum value symbol to a minimum value symbol and excludes any coded data word that has a transition from the minimum value symbol to the maximum value symbol; and
wherein the first coded data word is selected to minimize an absolute value of an RDS, unless a selection would produce a transition, with respect to a boundary symbol of another coded data word, that is between a maximum level and a minimum level.
9. The system of claim 8 , wherein the code space excludes all coded data words having a maximum value symbol as a boundary symbol.
10. The system of claim 8 , wherein the code space excludes all coded data words having a minimum value symbol as a boundary symbol.
11. The system of claim 8 , wherein a unique subset, for an n-bit data word of the first subset of n-bit data words, is assigned a coded data word having a maximum value symbol as a boundary symbol and a coded word having a non-maximum value symbol as a boundary symbol.
12. The system of claim 8 wherein a unique subset, for an n-bit data word of the first subset of n-bit data words, is assigned a coded data word having a minimum value symbol as a boundary symbol and a coded word having a non-minimum value symbol as a boundary symbol.
13. The system of claim 8 , further comprising:
a subsystem configured for scrambling the first n-bit data word, prior to using the first n-bit data word to determine the second n-bit data word.
14. The system of claim 8 , wherein each unique subset with a plurality of coded data words has at least two coded data words with 3 different weights.