Method and system for decoding low density parity check (LDPC) codes
An approach is provided for transmitting messages using low density parity check (LDPC) codes. Input messages are encoded according to a structured parity check matrix that imposes restrictions on a sub-matrix of the parity check matrix to generate LDPC codes. The LDPC codes are transmitted over a radio communication system (e.g., satellite network), wherein a receiver communicating over the radio communication system is configured to iteratively decode the received LDPC codes according to a signal constellation associated with the LDPC codes. The receiver is configured to iteratively regenerating signal constellation bit metrics after one or more decoding iterations.
1. A method comprising:
iteratively exchanging probability information with a low density parity check (LDPC) decoder to regenerate signal constellation bit metrics after one or more decoding iterations, wherein the signal constellation metrics are determined based on distance vector information,
wherein the decoder is configured to output decoded messages based on the regenerated signal constellation bit metrics.
2. A method according to claim 1 , wherein the probability information includes a posteriori probability information based on a priori probability information based on the distance vector information that includes information on distances between received noisy symbol points and symbol points of the signal constellation.
3. A method according to claim 2 , wherein the decoder is further configured to determine whether parity check equations associated with the LDPC codes are satisfied according to the a priori probability and the a posteriori probability information.
4. A method according to claim 2 , wherein the decoder is further configured to determine extrinsic information based on the a posteriori probability information and a priori probability information, and to output symbol probabilities associated with the signal constellation according to the extrinsic information.
5. A method according to claim 1 , wherein symbols of the signal constellation are Gray coded, whereby more vulnerable bits of Gray coded symbol constellation are assigned at least as many parity checks as less vulnerable bits of Gray coded symbol constellation.
6. A method according to claim 1 , wherein information regarding bit nodes and check nodes of the LDPC codes are stored in contiguous physical memory locations.
7. A method according to claims 1 , wherein the signal constellation Includes one of 31-PSK (Phase Shift Keying), 39-QAM (Quadrature Amplitude Modulation), or QPSK (Quadrature Phase Shift Keying).
8. A method according to claim 1 , wherein the LDPC codes are received over a satellite network.
9. An apparatus comprising:
a bit generator configured to iteratively exchange probability information with a low density parity check (LDPC) decoder to regenerate signal constellation bit metrics after one or more decoding iterations, wherein the signal constellation metrics are determined based on distance vector information,
wherein the decoder is configured to output decoded messages based on the regenerated signal constellation bit metrics.
10. An apparatus according to claim 9 , wherein the probability information includes a posteriori probability information based on a priori probability information based on the distance vector information that includes information on distances between received noisy symbol points and symbol points of the signal constellation.
11. An apparatus according to claim 10 , wherein the decoder is further configured to determine whether parity check equations associated with the LDPC codes are satisfied according to the a priori probability and the a posteriori probability information.
12. An apparatus according to claim 10 , wherein the decoder is further configured to determine extrinsic information based on the a posteriori probability information and a priori probability information, and to output symbol probabilities associated with the signal constellation according to the extrinsic information.
13. An apparatus according to claim 9 , wherein symbols of the signal constellation are Gray coded, whereby more vulnerable bits of Gray coded symbol constellation are assigned at least as many parity checks as less vulnerable bits of Gray coded symbol constellation.
14. An apparatus according to claim 9 , wherein information regarding bit nodes and check nodes of the LDPC codes are stored in contiguous physical memory locations.
15. An apparatus according to claims 9 , wherein the signal constellation includes one of 31-PSK (Phase Shift Keying), 39-QAM (Quadrature Amplitude Modulation), or QPSK (Quadrature Phase Shift Keying).
16. An apparatus according to claim 9 , wherein the LDPC codes are received over a satellite network.
17. A system comprising:
a low density purity check (LDPC) decoder configured to iteratively decode LDPC codes according to a signal constellation associated with the LDPC codes; and
a bit generator coupled to the decoder and to iteratively regenerate signal constellation bit metrics after one or more decoding iterations, wherein the signal constellation metrics are determined based an distance vector information,
wherein the decoder is further configured to output decoded messages based on the regenerated signal constellation bit metrics.
18. A system according to claim 17 , wherein the decoder is further configured to transmit a posteriori probability information based on the a priori probability information generated by the bit metric generator based the distance vector information, the decoder being further configured to determine whether parity check equations associated with the LDPC codes are satisfied according to the a priori probability and the a posteriori probability information.
19. A system according to claim 18 , wherein the distance vector information includes information on distances between received noisy symbol points and symbol points of the signal constellation.
20. A system according to claim 18 , wherein the decoder is further configured to determine extrinsic information based on the a posteriori probability information and a priori probability information, and to output symbol probabilities associated with the signal constellation according to the extrinsic information.