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394 lines
9.7 KiB
Fortran
394 lines
9.7 KiB
Fortran
subroutine bpdecode174b(llr,apmask,maxiterations,decoded,cw,nharderror,iter)
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!
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! A log-domain belief propagation decoder for the (174,91) code.
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!
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integer, parameter:: N=174, K=91, M=N-K
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integer*1 codeword(N),cw(N),apmask(N)
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integer colorder(N)
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integer*1 decoded(K)
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integer Nm(7,M)
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integer Mn(3,N) ! 3 checks per bit
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integer synd(M)
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real tov(3,N)
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real toc(7,M)
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real tanhtoc(7,M)
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real zn(N)
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real llr(N)
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real Tmn
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integer nrw(M)
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data colorder/ &
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0, 1, 2, 3, 28, 4, 5, 6, 7, 8, 9, 10, 11, 34, 12, 32, 13, 14, 15, 16,&
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17, 18, 36, 29, 40, 19, 20, 38, 21, 41, 30, 42, 22, 44, 37, 47, 48, 23, 33, 43,&
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49, 45, 56, 39, 25, 26, 46, 50, 51, 52, 24, 57, 58, 61, 31, 54, 64, 35, 27, 62,&
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59, 53, 60, 63, 55, 70, 66, 67, 68, 65, 71, 74, 72, 73, 77, 75, 69, 76, 79, 82,&
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83, 78, 81, 80, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99,&
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100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,&
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120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,&
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140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,&
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160,161,162,163,164,165,166,167,168,169,170,171,172,173/
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data Mn/ &
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1, 24, 66, &
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2, 5, 70, &
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3, 31, 65, &
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4, 49, 58, &
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6, 60, 67, &
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7, 32, 75, &
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8, 48, 82, &
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9, 35, 41, &
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10, 39, 62, &
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11, 14, 61, &
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12, 71, 74, &
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13, 23, 78, &
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15, 16, 79, &
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17, 54, 63, &
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18, 50, 57, &
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19, 30, 47, &
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20, 64, 80, &
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21, 28, 69, &
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22, 25, 43, &
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26, 34, 72, &
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27, 36, 37, &
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29, 40, 44, &
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33, 52, 53, &
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38, 55, 83, &
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42, 51, 59, &
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45, 76, 81, &
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46, 68, 77, &
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56, 67, 73, &
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1, 4, 5, &
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2, 47, 51, &
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3, 46, 82, &
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6, 24, 76, &
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7, 9, 16, &
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8, 10, 78, &
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11, 35, 55, &
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12, 38, 64, &
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13, 42, 83, &
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14, 27, 54, &
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15, 21, 34, &
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17, 44, 53, &
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18, 25, 28, &
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19, 33, 57, &
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20, 22, 73, &
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23, 40, 81, &
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26, 49, 68, &
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29, 71, 75, &
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30, 65, 79, &
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31, 36, 60, &
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32, 43, 77, &
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37, 62, 70, &
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39, 69, 74, &
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41, 52, 66, &
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45, 50, 61, &
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48, 63, 80, &
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56, 59, 72, &
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58, 64, 65, &
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1, 13, 28, &
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2, 48, 75, &
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3, 53, 69, &
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4, 11, 44, &
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5, 73, 79, &
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6, 12, 17, &
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7, 57, 60, &
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8, 15, 61, &
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9, 39, 59, &
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10, 19, 49, &
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14, 43, 52, &
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16, 54, 68, &
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18, 41, 63, &
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20, 36, 45, &
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21, 67, 77, &
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10, 22, 55, &
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23, 65, 72, &
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24, 27, 82, &
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25, 26, 29, &
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30, 35, 37, &
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31, 51, 66, &
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17, 32, 78, &
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33, 42, 76, &
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34, 70, 83, &
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38, 46, 81, &
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40, 62, 80, &
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45, 47, 74, &
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50, 56, 71, &
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7, 37, 58, &
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1, 16, 71, &
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2, 6, 61, &
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3, 22, 50, &
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4, 59, 77, &
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5, 41, 81, &
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8, 58, 74, &
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9, 20, 26, &
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11, 21, 31, &
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12, 66, 79, &
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13, 14, 57, &
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15, 33, 40, &
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18, 44, 82, &
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19, 69, 83, &
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23, 49, 63, &
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24, 29, 39, &
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25, 47, 56, &
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27, 55, 72, &
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28, 64, 70, &
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30, 48, 77, &
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32, 34, 45, &
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35, 68, 80, &
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36, 38, 52, &
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42, 43, 62, &
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46, 60, 78, &
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51, 54, 67, &
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53, 73, 75, &
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14, 73, 76, &
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1, 22, 30, &
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2, 35, 43, &
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3, 47, 63, &
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4, 25, 76, &
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5, 33, 78, &
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6, 20, 83, &
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7, 12, 72, &
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8, 54, 70, &
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9, 61, 65, &
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10, 34, 51, &
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11, 46, 75, &
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13, 39, 68, &
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15, 17, 56, &
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16, 23, 36, &
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18, 32, 55, &
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19, 31, 81, &
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21, 37, 71, &
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24, 57, 64, &
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26, 38, 48, &
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27, 49, 50, &
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28, 52, 59, &
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29, 41, 58, &
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40, 60, 74, &
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42, 44, 79, &
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51, 53, 80, &
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62, 67, 82, &
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23, 66, 69, &
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1, 53, 61, &
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2, 18, 39, &
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3, 4, 12, &
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5, 26, 74, &
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6, 30, 52, &
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7, 82, 83, &
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8, 35, 73, &
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9, 19, 67, &
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10, 64, 75, &
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11, 20, 33, &
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13, 45, 48, &
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3, 14, 40, &
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15, 43, 49, &
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16, 55, 76, &
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17, 62, 65, &
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21, 47, 78, &
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22, 59, 81, &
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24, 34, 63, &
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25, 37, 66, &
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27, 79, 80, &
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28, 60, 79, &
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29, 31, 70, &
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32, 58, 69, &
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10, 36, 77, &
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38, 50, 51, &
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13, 41, 56, &
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42, 63, 71, &
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44, 47, 68, &
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1, 46, 72, &
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54, 57, 75, &
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2, 33, 58, &
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4, 17, 83, &
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5, 14, 55, &
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6, 23, 48, &
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7, 52, 56/
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data Nm/ &
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1, 29, 57, 86, 113, 140, 168, &
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2, 30, 58, 87, 114, 141, 170, &
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3, 31, 59, 88, 115, 142, 151, &
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4, 29, 60, 89, 116, 142, 171, &
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2, 29, 61, 90, 117, 143, 172, &
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5, 32, 62, 87, 118, 144, 173, &
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6, 33, 63, 85, 119, 145, 174, &
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7, 34, 64, 91, 120, 146, 0, &
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8, 33, 65, 92, 121, 147, 0, &
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9, 34, 66, 72, 122, 148, 163, &
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10, 35, 60, 93, 123, 149, 0, &
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11, 36, 62, 94, 119, 142, 0, &
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12, 37, 57, 95, 124, 150, 165, &
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10, 38, 67, 95, 112, 151, 172, &
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13, 39, 64, 96, 125, 152, 0, &
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13, 33, 68, 86, 126, 153, 0, &
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14, 40, 62, 78, 125, 154, 171, &
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15, 41, 69, 97, 127, 141, 0, &
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16, 42, 66, 98, 128, 147, 0, &
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17, 43, 70, 92, 118, 149, 0, &
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18, 39, 71, 93, 129, 155, 0, &
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19, 43, 72, 88, 113, 156, 0, &
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12, 44, 73, 99, 126, 139, 173, &
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1, 32, 74, 100, 130, 157, 0, &
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19, 41, 75, 101, 116, 158, 0, &
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20, 45, 75, 92, 131, 143, 0, &
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21, 38, 74, 102, 132, 159, 0, &
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18, 41, 57, 103, 133, 160, 0, &
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22, 46, 75, 100, 134, 161, 0, &
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16, 47, 76, 104, 113, 144, 0, &
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3, 48, 77, 93, 128, 161, 0, &
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6, 49, 78, 105, 127, 162, 0, &
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23, 42, 79, 96, 117, 149, 170, &
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20, 39, 80, 105, 122, 157, 0, &
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8, 35, 76, 106, 114, 146, 0, &
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21, 48, 70, 107, 126, 163, 0, &
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21, 50, 76, 85, 129, 158, 0, &
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24, 36, 81, 107, 131, 164, 0, &
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9, 51, 65, 100, 124, 141, 0, &
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22, 44, 82, 96, 135, 151, 0, &
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8, 52, 69, 90, 134, 165, 0, &
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25, 37, 79, 108, 136, 166, 0, &
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19, 49, 67, 108, 114, 152, 0, &
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22, 40, 60, 97, 136, 167, 0, &
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26, 53, 70, 83, 105, 150, 0, &
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27, 31, 81, 109, 123, 168, 0, &
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16, 30, 83, 101, 115, 155, 167, &
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7, 54, 58, 104, 131, 150, 173, &
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4, 45, 66, 99, 132, 152, 0, &
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15, 53, 84, 88, 132, 164, 0, &
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25, 30, 77, 110, 122, 137, 164, &
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23, 52, 67, 107, 133, 144, 174, &
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23, 40, 59, 111, 137, 140, 0, &
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14, 38, 68, 110, 120, 169, 0, &
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24, 35, 72, 102, 127, 153, 172, &
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28, 55, 84, 101, 125, 165, 174, &
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15, 42, 63, 95, 130, 169, 0, &
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4, 56, 85, 91, 134, 162, 170, &
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25, 55, 65, 89, 133, 156, 0, &
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5, 48, 63, 109, 135, 160, 0, &
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10, 53, 64, 87, 121, 140, 0, &
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9, 50, 82, 108, 138, 154, 0, &
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14, 54, 69, 99, 115, 157, 166, &
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17, 36, 56, 103, 130, 148, 0, &
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3, 47, 56, 73, 121, 154, 0, &
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1, 52, 77, 94, 139, 158, 0, &
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5, 28, 71, 110, 138, 147, 0, &
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27, 45, 68, 106, 124, 167, 0, &
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18, 51, 59, 98, 139, 162, 0, &
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2, 50, 80, 103, 120, 161, 0, &
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11, 46, 84, 86, 129, 166, 0, &
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20, 55, 73, 102, 119, 168, 0, &
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28, 43, 61, 111, 112, 146, 0, &
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11, 51, 83, 91, 135, 143, 0, &
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6, 46, 58, 111, 123, 148, 169, &
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26, 32, 79, 112, 116, 153, 0, &
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27, 49, 71, 89, 104, 163, 0, &
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12, 34, 78, 109, 117, 155, 0, &
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13, 47, 61, 94, 136, 159, 160, &
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17, 54, 82, 106, 137, 159, 0, &
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26, 44, 81, 90, 128, 156, 0, &
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7, 31, 74, 97, 138, 145, 0, &
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24, 37, 80, 98, 118, 145, 171/
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data nrw/ &
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7,7,7,7,7,7,7,6,6,7,6,6,7,7,6,6,7,6, &
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6,6,6,6,7,6,6,6,6,6,6,6,6,6,7,6,6,6, &
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6,6,6,6,6,6,6,6,6,6,7,7,6,6,7,7,6,6, &
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7,7,6,7,6,6,6,6,7,6,6,6,6,6,6,6,6,6, &
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6,6,7,6,6,6,7,6,6,6,7/
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ncw=3
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decoded=0
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toc=0
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tov=0
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tanhtoc=0
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! initialize messages to checks
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do j=1,M
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do i=1,nrw(j)
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toc(i,j)=llr((Nm(i,j)))
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enddo
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enddo
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ncnt=0
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do iter=0,maxiterations
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! Update bit log likelihood ratios (tov=0 in iteration 0).
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do i=1,N
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if( apmask(i) .ne. 1 ) then
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zn(i)=llr(i)+sum(tov(1:ncw,i))
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else
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zn(i)=llr(i)
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endif
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enddo
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! Check to see if we have a codeword (check before we do any iteration).
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cw=0
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where( zn .gt. 0. ) cw=1
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ncheck=0
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do i=1,M
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synd(i)=sum(cw(Nm(1:nrw(i),i)))
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if( mod(synd(i),2) .ne. 0 ) ncheck=ncheck+1
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! if( mod(synd(i),2) .ne. 0 ) write(*,*) 'check ',i,' unsatisfied'
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enddo
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! write(*,*) 'number of unsatisfied parity checks ',ncheck
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if( ncheck .eq. 0 ) then ! we have a codeword - reorder the columns and return it
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codeword=cw(colorder+1)
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decoded=codeword(M+1:N)
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nerr=0
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do i=1,N
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if( (2*cw(i)-1)*llr(i) .lt. 0.0 ) nerr=nerr+1
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enddo
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nharderror=nerr
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return
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endif
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if( iter.gt.0 ) then ! this code block implements an early stopping criterion
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! if( iter.gt.10000 ) then ! this code block implements an early stopping criterion
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nd=ncheck-nclast
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if( nd .lt. 0 ) then ! # of unsatisfied parity checks decreased
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ncnt=0 ! reset counter
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else
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ncnt=ncnt+1
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endif
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! write(*,*) iter,ncheck,nd,ncnt
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if( ncnt .ge. 5 .and. iter .ge. 10 .and. ncheck .gt. 15) then
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nharderror=-1
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return
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endif
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endif
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nclast=ncheck
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! Send messages from bits to check nodes
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do j=1,M
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do i=1,nrw(j)
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ibj=Nm(i,j)
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toc(i,j)=zn(ibj)
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do kk=1,ncw ! subtract off what the bit had received from the check
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if( Mn(kk,ibj) .eq. j ) then
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toc(i,j)=toc(i,j)-tov(kk,ibj)
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endif
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enddo
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enddo
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enddo
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! send messages from check nodes to variable nodes
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do i=1,M
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tanhtoc(1:6,i)=tanh(-toc(1:6,i)/2)
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enddo
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do j=1,N
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do i=1,ncw
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ichk=Mn(i,j) ! Mn(:,j) are the checks that include bit j
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Tmn=product(tanhtoc(1:nrw(ichk),ichk),mask=Nm(1:nrw(ichk),ichk).ne.j)
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call platanh(-Tmn,y)
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! y=atanh(-Tmn)
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tov(i,j)=2*y
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enddo
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enddo
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enddo
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nharderror=-1
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return
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end subroutine bpdecode174b
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