LDU decoding, more fake decoders
git-svn-id: http://op25.osmocom.org/svn/trunk@26 65a5c917-d112-43f1-993d-58c26a4786be
This commit is contained in:
mossmann
parent
60d58f6415
commit
0c59829ff7
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@ -97,9 +97,10 @@ def trellis_1_2_decode(input):
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#print output
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return output
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# fake (63,16,23) BCH decoder, no error correction
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# fake (64,16,23) BCH decoder, no error correction
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# spec sometimes refers to this as (63,16,23) plus a parity bit
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# TODO: make less fake
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def bch_63_16_23_decode(input):
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def bch_64_16_23_decode(input):
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return input[:8]
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# fake (18,6,8) shortened Golay decoder, no error correction
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@ -111,11 +112,6 @@ def golay_18_6_8_decode(input):
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output.extend(codeword[:3])
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return output
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# fake (36,20,17) Reed-Solomon decoder, no error correction
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# TODO: make less fake
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def rs_36_20_17_decode(input):
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return input[:60]
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# fake (24,12,8) extended Golay decoder, no error correction
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# TODO: make less fake
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def golay_24_12_8_decode(input):
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@ -125,11 +121,59 @@ def golay_24_12_8_decode(input):
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output.extend(codeword[:6])
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return output
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# fake (10,6,3) shortened Hamming decoder, no error correction
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# TODO: make less fake
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def hamming_10_6_3_decode(input):
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output = []
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for i in range(0,len(input),5):
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codeword = input[i:i+5]
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output.extend(codeword[:3])
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return output
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# fake (24,12,13) Reed-Solomon decoder, no error correction
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# TODO: make less fake
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def rs_24_12_13_decode(input):
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return input[:36]
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# fake (24,16,9) Reed-Solomon decoder, no error correction
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# TODO: make less fake
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def rs_24_16_9_decode(input):
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return input[:48]
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# fake (36,20,17) Reed-Solomon decoder, no error correction
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# TODO: make less fake
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def rs_36_20_17_decode(input):
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return input[:60]
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# fake (16_8_5) shortened cyclic decoder, no error correction
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# TODO: make less fake
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def cyclic_16_8_5_decode(input):
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output = []
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for i in range(0,len(input),8):
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codeword = input[i:i+8]
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output.extend(codeword[:4])
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return output
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# fake IMBE frame decoder
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# TODO: make less fake
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#
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# each IMBE frame encodes 20 ms of voice in 88 bits
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# words u_0, u_1, . . . u_7 may be encrypted
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# 56 coding bits added for total of 144 bits
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# 48 most important bits protected by (23,12,7) Golay code
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# (u_0, u_1, u_2, u_3 12 bits each)
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# TODO: Golay decoding
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# next 33 important bits protected by (15,11,3 Hamming code
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# (u_4, u_5, u_6, 11 bits each)
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# TODO: Hamming decoding
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# 7 least important bits unprotected
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# (u_7 7 bits)
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# words u_1, u_2, . . . u_6 are further xored by PN based on u_0
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# TODO: de-randomization
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# TODO: de-interleaving
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def imbe_decode(input):
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print "Raw IMBE frame: 0x%0x" % (symbols_to_integer(input))
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# collect input sample statistics for normalization
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total_value = 0.0
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total_deviation = 0.0
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@ -225,7 +269,7 @@ print "frame sync: 0x%012x" % symbols_to_integer(symbols[0:24])
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# extract Network Identifier from in between status symbols
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nid_symbols = symbols[24:35] + symbols[36:57]
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network_id = bch_63_16_23_decode(nid_symbols)
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network_id = bch_64_16_23_decode(nid_symbols)
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network_access_code = symbols_to_integer(network_id[:6])
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data_unit_id = symbols_to_integer(network_id[6:])
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@ -290,75 +334,69 @@ elif data_unit_id == 15:
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golay_codewords = terminator_symbols[:144]
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rs_codeword = golay_24_12_8_decode(golay_codewords)
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link_control = rs_24_12_13_decode(rs_codeword)
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print "Link Control: 0x%09x" % (symbols_to_integer(link_control))
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print "Link Control: 0x%018x" % (symbols_to_integer(link_control))
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elif data_unit_id == 5:
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print "found a Logical Link Data Unit 1 (LDU1)"
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# contains voice frames 1 through 9 of a superframe
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#
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# each IMBE frame encodes 20 ms of voice in 88 bits
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# words u_0, u_1, . . . u_7 may be encrypted
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# 56 coding bits added for total of 144 bits
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# 48 most important bits protected by (23,12,7) Golay code
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# (u_0, u_1, u_2, u_3 12 bits each)
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# TODO: Golay decoding
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# next 33 important bits protected by (15,11,3 Hamming code
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# (u_4, u_5, u_6, 11 bits each)
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# TODO: Hamming decoding
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# 7 least important bits unprotected
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# (u_7 7 bits)
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# words u_1, u_2, . . . u_6 are further xored by PN based on u_0
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# TODO: de-randomization
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# TODO: de-interleaving
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ldu_symbols = symbols[57:864]
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status_symbols = extract_status_symbols(ldu_symbols)
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imbe1_symbols = ldu_symbols[:72]
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imbe2_symbols = ldu_symbols[72:144]
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imbe3_symbols = ldu_symbols[164:236]
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imbe4_symbols = ldu_symbols[256:328]
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imbe5_symbols = ldu_symbols[348:420]
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imbe6_symbols = ldu_symbols[440:512]
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imbe7_symbols = ldu_symbols[532:604]
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imbe8_symbols = ldu_symbols[624:696]
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imbe9_symbols = ldu_symbols[712:784]
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lc_symbols = ldu_symbols[144:164] + ldu_symbols[236:256] + ldu_symbols[328:348] + ldu_symbols[420:440] + ldu_symbols[512:532] + ldu_symbols[604:624]
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lsd_symbols = ldu_symbols[696:712]
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# + Link Control Word (LC): 72 bits data, 168 bits parity
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# variable format specified by first field:
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# Link Control Format (LCF) 8 bits
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# rest of frame is 64 bits of fields specified by LCF
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# likeliy to include TGID, Source ID, Destination ID, Emergency indicator, MFID
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# 72 bits encoded with (24,12,13) Reed Solomon code and then (10,6,3) shortened Hamming code
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# total length encoded: 240 bits
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# TODO: decode
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# + Low Speed Data: 32 bits data, 32 bits parity
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# 32 bits encoded with (16,8,5) shortened cyclic code
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# total length encoded: 64 bits
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# huh? Is the other half in LDU2?
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# TODO: decode
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imbe_symbols = []
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imbe_symbols.append(ldu_symbols[:72])
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imbe_symbols.append(ldu_symbols[72:144])
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imbe_symbols.append(ldu_symbols[164:236])
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imbe_symbols.append(ldu_symbols[256:328])
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imbe_symbols.append(ldu_symbols[348:420])
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imbe_symbols.append(ldu_symbols[440:512])
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imbe_symbols.append(ldu_symbols[532:604])
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imbe_symbols.append(ldu_symbols[624:696])
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imbe_symbols.append(ldu_symbols[712:784])
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for frame in imbe_symbols:
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imbe_decode(frame)
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link_control_symbols = ldu_symbols[144:164] + ldu_symbols[236:256] + ldu_symbols[328:348] + ldu_symbols[420:440] + ldu_symbols[512:532] + ldu_symbols[604:624]
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low_speed_data_symbols = ldu_symbols[696:712]
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link_control_rs_codeword = hamming_10_6_3_decode(link_control_symbols)
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link_control = rs_24_12_13_decode(link_control_rs_codeword)
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print "Link Control: 0x%018x" % (symbols_to_integer(link_control))
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link_control_format = link_control[:4]
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print "Link Control Format: 0x%02x" % (symbols_to_integer(link_control_format))
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# rest of link control frame is 64 bits of fields specified by LCF
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# likeliy to include TGID, Source ID, Destination ID, Emergency indicator, MFID
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low_speed_data = cyclic_16_8_5_decode(low_speed_data_symbols)
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print "Low Speed Data: 0x%04x" % (symbols_to_integer(low_speed_data))
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# spec says Low Speed Data = 32 bits data + 32 bits parity
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# huh? Is the other half in LDU2?
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elif data_unit_id == 10:
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print "found a Logical Link Data Unit 2 (LDU2)"
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# contains voice frames (codewords) 10 through 18 of a superframe
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print "found a Logical Link Data Unit 2 (LDU2)"
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ldu_symbols = symbols[57:864]
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status_symbols = extract_status_symbols(ldu_symbols)
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imbe10_symbols = ldu_symbols[:72]
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imbe11_symbols = ldu_symbols[72:144]
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imbe12_symbols = ldu_symbols[164:236]
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imbe13_symbols = ldu_symbols[256:328]
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imbe14_symbols = ldu_symbols[348:420]
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imbe15_symbols = ldu_symbols[440:512]
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imbe16_symbols = ldu_symbols[532:604]
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imbe17_symbols = ldu_symbols[624:696]
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imbe_symbols = ldu_symbols[712:784]
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esd_symbols = ldu_symbols[144:164] + ldu_symbols[236:256] + ldu_symbols[328:348] + ldu_symbols[420:440] + ldu_symbols[512:532] + ldu_symbols[604:624]
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lsd_symbols = ldu_symbols[696:712]
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# TODO: decode
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# + Encryption Sync Word
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# Message Indicator (MI) 72 bits
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#message_indicator =
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# Algorithm ID (ALGID) 8 bits
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#algorithm_id =
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# Key ID (KID) 16 bits
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#key_id =
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# 96 bits encoded with (24,16,9) Reed Solomon code and then (10,6,3) shortened Hamming code
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imbe_symbols = []
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imbe_symbols.append(ldu_symbols[:72])
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imbe_symbols.append(ldu_symbols[72:144])
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imbe_symbols.append(ldu_symbols[164:236])
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imbe_symbols.append(ldu_symbols[256:328])
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imbe_symbols.append(ldu_symbols[348:420])
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imbe_symbols.append(ldu_symbols[440:512])
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imbe_symbols.append(ldu_symbols[532:604])
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imbe_symbols.append(ldu_symbols[624:696])
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imbe_symbols.append(ldu_symbols[712:784])
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for frame in imbe_symbols:
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imbe_decode(frame)
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encryption_sync_symbols = ldu_symbols[144:164] + ldu_symbols[236:256] + ldu_symbols[328:348] + ldu_symbols[420:440] + ldu_symbols[512:532] + ldu_symbols[604:624]
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low_speed_data_symbols = ldu_symbols[696:712]
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encryption_sync_rs_codeword = hamming_10_6_3_decode(encryption_sync_symbols)
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encryption_sync = rs_24_16_9_decode(encryption_sync_rs_codeword)
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print "Encryption Sync Word: 0x%024x" % (symbols_to_integer(encryption_sync))
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# Message Indicator (MI) 72 bits
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message_indicator = encryption_sync[:36]
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print "Message Indicator: 0x%018x" % (symbols_to_integer(message_indicator))
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# Algorithm ID (ALGID) 8 bits
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algorithm_id = encryption_sync[36:40]
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print "Algorithm ID: 0x%02x" % (symbols_to_integer(algorithm_id))
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# Key ID (KID) 16 bits
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key_id = encryption_sync[40:48]
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print "Key ID: 0x%04x" % (symbols_to_integer(key_id))
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low_speed_data = cyclic_16_8_5_decode(low_speed_data_symbols)
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print "Low Speed Data: 0x%04x" % (symbols_to_integer(low_speed_data))
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else:
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print "unknown Data Unit ID"
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