Decoder for a system with H-ARQ with cross-packet coding
View Patent ↗An H-ARQ system wherein the transmission of two consecutive, or sequential, blocks of information bits are considered jointly; i.e., one of the blocks of information being embedded within the other one of the blocks of information. If a retransmission for the first block is necessary, the system processes both blocks jointly. The system is provided with cross-packet coding which extends current H-ARQ schemes for point-to-point communications wherein the transmission of two consecutive block of information bits is considered jointly. If a retransmission for the first block is necessary, the system processes both blocks jointly. This allows both blocks to be decoded without errors at the receiver after the retransmission.
1. An apparatus comprising:
a receiver configured to:
receive at least a fragment of a first codeword, the first codeword being based on a first packet; and
receive at least a fragment of a second codeword, the second codeword being based on cross-coding the first packet and the second packet;
a memory configured to store the at least the fragment of the first codeword and the at least the fragment of the second codeword;
an first iterative decoder, the iterative decoder including a first codeword input and a second codeword input, the first iterative decoder being configured to iteratively decode the first packet by passing the at least the fragment of the first codeword through the first codeword input and passing equally probable values through the second codeword input; and
a second iterative decoder configured to iteratively decode the second packet jointly with the first packet by using the decoded first codeword to decode the second codeword.
2. The apparatus of claim 1 , wherein the second iterative decoder is configured to iteratively decode the second packet jointly with the first packet by using the decoded first codeword as a priori information to decode the second codeword.
3. The apparatus of claim 1 , wherein the first iterative decoder and the second iterative decoder are configured to iteratively pass information associated with the first codeword to each other to decode the first codeword and the second codeword.
4. The apparatus of claim 1 , wherein the first codeword and the second codeword are coded by a linear channel code.
5. The apparatus of claim 1 , wherein the first codeword and the second codeword are coded by a low-density parity check (LDPC) code.
6. The apparatus of claim 1 , wherein the receiver is configured to receive the at least the fragment of the first codeword and the at least the fragment of the second codeword via a wireless medium.
7. The apparatus of claim 1 , further comprising a transmitter configured to transmit a jointly coded packet.
8. The apparatus of claim 1 , wherein the apparatus further includes:
a first summer configured to sum the first at least the fragment with an output of a second summer and output the sum to the first iterative decoder;
the second summer configured to subtract an output of a third summer from a second message output received from the second iterative decoder and output a difference to the first summer and to the third summer;
the third summer configured to subtract the difference received from the second summer from the decoded sum received from the first iterative decoder and output a difference to the second summer and to a fourth summer;
the fourth summer configured to sum the second at least the fragment with the difference received from the third summer and output the sum to the second iterative decoder;
wherein the first iterative decoder is configured to decode the sum received from the first summer and output the decoded sum to a first message output and to the third summer; and
wherein the second iterative decoder is configured to decode the sum received from the fourth summer and output the decoded difference to a second message output and to the second summer.
9. The apparatus of claim 8 , wherein:
the first decoder is configured to decode the sum received from the first summer by calculating a posteriori reliabilities from the first at least the fragment; and
the second channel decoder is configured to decode the difference by calculating a posteriori reliabilities from the difference received from the fourth summer and from the a posteriori reliabilities calculated by the first channel decoder.
10. The apparatus of claim 8 , wherein:
the first decoder is configured to decode the sum received from the first summer by a first belief propagation decoding algorithm; and
the second channel decoder is configured to decode the difference by a second belief propagation decoding algorithm.
11. The apparatus of claim 1 , further comprising a first value restorer configured to restore punctured values to the at least the fragment of the first codeword and a second value restorer configured to restore punctured values to the at least the fragment of the second codeword.
12. An apparatus comprising:
a receiver configured to:
receive at least a fragment of a first codeword, the first codeword being based on a first packet; and
receive at least a fragment of a second codeword, the second codeword being based on cross-coding the first packet and the second packet;
a memory configured to store the at least the fragment of the first codeword and the at least the fragment of the second codeword; and
a decoder configured to:
construct a combined codeword matrix based on a first codeword matrix and the second codeword; and
estimate the first packet and the second packet based on predefined criteria associated with the codeword matrix, the error associated with the combined codeword matrix.
13. The apparatus of claim 12 , wherein the receiver is configured to receive the at least the fragment of the first codeword and the at least the fragment of the second codeword via a wireless medium.
14. The apparatus of claim 12 , wherein the codewords are constructed from a low density parity check (LDPC) matrix.
15. The apparatus of claim 12 , wherein the parity-check matrix is based on a first codeword parity check matrix which is based on the first codeword and a second codeword parity check matrix which is based on the second codeword.
16. The apparatus of claim 15 , wherein the parity-check matrix is
[
H
11
H
12
0
H
21
0
H
22
]
wherein H 1 =[H 11 H 12 ], H 2 =[H 21 H 22 ], H 1 x 1 =0, H 2 x 2 =0, x 1 =[x 0 ; x 12 ] is the first codeword, and x 2 =[x 0 ; x 22 ] is the second codeword wherein x 0 contains common bits between x 1 and x 2 .
17. The apparatus of claim 12 , wherein the decoder is further configured to construct the combined codeword based on only the at least the fragment of the first codeword and by substituting equally probable values for the at least the fragment of the second codeword during the first decoding.
18. The apparatus of claim 12 , further comprising a first value restorer configured to restore punctured values to the at least the fragment of the first codeword and a second value restorer configured to restore punctured values to the at least the fragment of the second codeword.