Apparatus, systems and methods including nonbinary low density parity check coding for enhanced multicarrier underwater acoustic communications
Advantageous underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. The apparatus, systems and methods employ nonbinary low density parity check (LDPC) codes that achieve excellent performance and match well with the underlying modulation. The nonbinary LDPC codes of the proposed apparatus, systems and methods are formed, at least in part, from a generator matrix that has a high density to reduce the peak-to-average-power ratio (PAPR) with minimal overhead. The disclosed apparatus, systems and methods employ nonbinary regular LDPC cycle codes if the constellation is large and nonbinary irregular LDPC codes if the constellation is small or moderate. The nonbinary irregular and regular LDPC codes enable: i) parallel processing in linear-time encoding; ii) parallel processing in sequential belief propagation decoding; and iii) considerable resource reduction on the code storage for encoding and decoding.
1. A method for underwater acoustic (UWA) communication, the method comprising the steps of:
(a) providing at least one nonbinary, low density parity check (LDPC) code to an encoder;
(b) with the encoder, encoding: (i) at least one nonbinary regular LDPC code if the constellation size of the at least one nonbinary LDPC code is a modulation of at least 64-QAM or a Galois Field of at least 64, or (ii) at least one nonbinary irregular LDPC code if the constellation size of the at least one nonbinary LDPC code is a modulation of less than 64-QAM or a Galois Field of less than 64;
(c) transmitting the at least one encoded LDPC code through an underwater transmitter on an orthogonal frequency division multiplexed (OFDM) UWA signal;
(d) receiving the at least one encoded LDPC code through an underwater receiver on the OFDM UWA signal;
(e) storing the received at least one encoded LDPC code; and
(f) decoding the received at least one encoded LDPC code.
2. The method of claim 1 , wherein the at least one nonbinary regular LDPC code has a parity check matrix with a fixed column weight of 2 and a fixed row weight.
3. The method of claim 2 , wherein the nonbinary regular LDPC code's parity check matrix can be put into a concatenation form of row-permuted block-diagonal matrices after row and column permutations if: (i) the row weight is even, or (ii) the row weight is odd and the nonbinary regular LDPC code's associated graph contains at least one spanning subgraph that includes disjoint edges.
4. The method of claim 1 , wherein the at least one nonbinary irregular LDPC code has a parity check matrix with a first portion that is substantially similar to the parity check matrix of the at least one nonbinary regular LDPC code and a second portion that has a column weight greater than the column weight of the parity check matrix of the nonbinary regular LDPC code.
5. The method of claim 1 , wherein the step of encoding is performed in parallel and in linear time.
6. The method of claim 1 , wherein the step of decoding includes parallel processing in sequential belief propagation decoding.
7. The method of claim 1 , wherein the received at least one nonbinary LDPC code is stored in memory associated with a processor.
8. The method of claim 1 , further including the step of designing the at least one nonbinary LDPC code; and
wherein the step of designing the at least one nonbinary LDPC code includes determining the code structure design.
9. The method of claim 8 , wherein the code structure design is determined based on a regular graph, a computer search or the equivalent form of the check matrix.
10. The method of claim 8 , wherein the step of designing the at least one nonbinary LDPC code includes determining the nonzero entries; and
wherein nonzero entries are chosen to increase the number of irresolvable cycles.
11. The method of claim 1 , wherein the at least one nonbinary irregular LDPC code or the at least one nonbinary regular LDPC code reduces the peak-to-average power ratio of the OFDM signal.
12. An underwater acoustic (UWA) communications system comprising:
(a) an encoder adapted to receive at least one nonbinary, LDPC code and to encode: (i) at least one nonbinary regular LDPC code if the constellation size of the at least one nonbinary LDPC code is a modulation of at least 64-QAM or a Galois Field of at least 64, or (ii) at least one nonbinary irregular LDPC code if the constellation size of the at least one nonbinary LDPC code is a modulation of less than 64-QAM or a Galois Field of less than 64;
(b) an underwater transmitter in communication with the encoder, the underwater transmitter adapted to transit the at least one encoded LDPC code through an orthogonal frequency division multiplexed (OFDM) UWA signal;
(c) one or more underwater receiving elements adapted to receive the at least one encoded LDPC code on the OFDM UWA signal;
(d) memory adapted to store the received at least one encoded LDPC code; and
(e) a decoder adapted to decode the received at least one encoded LDPC code.
13. The system of claim 12 , wherein the at least one nonbinary regular LDPC code has a parity check matrix with a fixed column weight of 2 and a fixed row weight.
14. The system of claim 13 , wherein the nonbinary regular LDPC code's parity check matrix can be put into a concatenation form of row-permuted block-diagonal matrices after row and column permutations if: (i) the row weight is even, or (ii) the row weight is odd and the nonbinary regular LDPC code's associated graph contains at least one spanning subgraph that includes disjoint edges.
15. The system of claim 14 , wherein the at least one nonbinary irregular LDPC code or the at least one nonbinary regular LDPC code reduces the peak-to-average power ratio of the OFDM signal.
16. The system of claim 12 , wherein the at least one nonbinary irregular LDPC code has a parity check matrix with a first portion that is substantially similar to the parity check matrix of the at least one nonbinary regular LDPC code and a second portion that has a column weight greater than the column weight of the parity check matrix of the nonbinary regular LDPC code.
17. The system of claim 12 , wherein the step of encoding is performed in parallel and in linear time.
18. The system of claim 12 , wherein the step of decoding includes parallel processing in sequential belief propagation decoding.
19. The system of claim 12 , further including the step of designing the at least one nonbinary LDPC code; and
wherein the step of designing the at least one LDPC code includes determining the code structure design.
20. The system of claim 19 , wherein the code structure design is determined based on a regular graph, a computer search or the equivalent form of the check matrix.
21. The method of claim 19 , wherein the step of designing the at least one LDPC code includes determining the nonzero entries; and
wherein nonzero entries are chosen to increase the number of irresolvable cycles.