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git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@6168 19bc5d8c-e614-43d4-8b26-e1612bc8e597
60 lines
2.8 KiB
Plaintext
60 lines
2.8 KiB
Plaintext
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SACCH Encoding:
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(Parity(0x10004820009ULL,40,224)
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Set bits: 0,3,17,23,26,40
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g(D) = 1 + D3 + D17 + D23 + D26 + D40
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From GSM05.03 sec5.1
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184 bits
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Parity:
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a) Parity bits:
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The block of 184 information bits is protected by 40 extra bits used
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for error correction and detection. These bits are added to the 184 bits
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according to a shortened binary cyclic code (FIRE code) using the generator
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polynomial:
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g(D) = (D23 + 1)*(D17 + D3 + 1)
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The encoding of the cyclic code is performed in a systematic form, which means that, in GF(2), the polynomial:
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d(0)D223 + d(1)D222 +...+d(183)D40 + p(1)D38 +...+p(38)D + p(39)
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where {p(0),p(1),...,p(39)} are the parity bits , when divided by g(D) yields a remainder equal to:
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1 + D + D2 +...+ D39.
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) Tail bits
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Four tail bits equal to 0 are added to the information and parity bits, the result being a block of 228 bits.
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u(k) = d(k) for k= 0,1,...,183
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u(k) = p(k-184) for k = 184,185,...,223
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u(k) = 0 for k = 224,225,226,227 (tail bits)
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From GSM03.64 sec6.5.5
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CS-4: 431 bits.
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----
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a) USF precoding:
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The first three bits d(0),d(1),d(2) are block coded into twelve bits u'(0),u'(1),...,u'(11) according to the following
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table:
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d(0),d(1),d(2) u'(0),u'(1),...,u'(11)
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000 000 000 000 000
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001 000 011 011 101
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010 001 101 110 110
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011 001 110 101 011
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100 110 100 001 011
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101 110 111 010 110
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110 111 001 111 101
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111 111 010 100 000
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b) Parity bits:
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Sixteen parity bits p(0),p(1),...,p(15) are defined in such a way that in GF(2) the binary polynomial:
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d(0)D446 +...+ d(430)D16 + p(0)D15 +...+ p(15), when divided by:
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D16 + D12 + D5 + 1, yields a remainder equal to:
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D15 + D14 + D13 + D12 + D11 + D10 + D9 + D8 + D7 + D6 + D5 + D4 + D3 + D2 + D+1.
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The result is a block of 456 coded bits, {c(0),c(1),...,c(455)}:
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c(k) = u'(k) for k = 0,1,...,11
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c(k) = d(k-9) for k = 12,13,...,439
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c(k) = p(k-440) for k = 440,441,...,455
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5.1.4.5 Mapping on a burst
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The mapping is given by the rule:
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e(B,j) = i(B,j) and e(B,59+j) = i(B,57+j) for j = 0,1,...,56
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and
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e(B+m,57) = q(2m) and e(B+m,58) = q(2m+1) for m = 0,1,2,3
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where
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q(0),q(1),...,q(7) = 0,0,0,1,0,1,1,0 identifies the coding scheme CS-4.
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