OsmocomTETRA » History » Version 4
laforge, 02/19/2016 10:52 PM
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1 | 2 | laforge | = Osmocom TETRA MAC/PHY layer experimentation code = |
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2 | 1 | ||
3 | 2 | laforge | This code aims to implement the sending and receiving part of the |
4 | TETRA MAC/PHY layer. |
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5 | 1 | ||
6 | 2 | laforge | If you read the ETSI EN 300 392-2 (TETRA V+D Air Interface), you will |
7 | find this code implementing the parts between the MAC-blocks (called |
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8 | type-1 bits) and the bits that go to the DQPSK-modulator (type-5 bits). |
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9 | 1 | ||
10 | 3 | laforge | It is most useful to look at Figure 8.5, 8.6, 9.3 and 19.12 of the |
11 | abovementioned specification in conjunction with this program. |
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12 | 1 | ||
13 | 3 | laforge | |
14 | == Source Code == |
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15 | The source code is available via read-only git access at |
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16 | {{{ |
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17 | git clone git://git.osmocom.org/osmo-tetra.git |
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18 | }}} |
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19 | |||
20 | 4 | laforge | You can also browse the source code at nttp://cgit.osmocom.org/ |
21 | 3 | laforge | |
22 | 1 | You will need [http://bb.osmocom.org/trac/wiki/libosmocore libosmocore] to link. |
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23 | 3 | laforge | |
24 | == Mailing List == |
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25 | There is a public mailing list regarding development of this project, you can |
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26 | visit the subscription page at https://lists.osmocom.org/mailman/listinfo/tetra |
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27 | |||
28 | This list is '''for discussion between software developers''' who intend to improve the |
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29 | Osmocom TETRA software. It is not a forum for individuals asking how they can tap |
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30 | into police radio (which is encrypted anyway). |
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31 | 1 | ||
32 | 2 | laforge | == Demodulator == |
33 | 1 | ||
34 | 2 | laforge | src/demod/python/cpsk.py |
35 | * contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI |
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36 | src/demod/python/tetra-demod.py |
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37 | * call demodulator on a 'cfile' containing complex baseband samples |
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38 | src/demod/python/usrp1-tetra_demod.py |
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39 | * use demodulator in realtime with a USRP1 SDR |
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40 | src/demod/python/usrp2-tetra_demod.py |
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41 | * use demodulator in realtime with a USRP2 SDR |
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42 | 1 | ||
43 | 2 | laforge | The output of the demodulator is a file containing one float value for each symbol, |
44 | containing the phase shift (in units of pi/4) relative to the previous symbol. |
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45 | 1 | ||
46 | 2 | laforge | You can use the "float_to_bits" program to convert the float values to unpacked |
47 | bits, i.e. 1-bit-per-byte |
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48 | 1 | ||
49 | |||
50 | 2 | laforge | == PHY/MAC layer == |
51 | |||
52 | === library code === |
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53 | |||
54 | Specifically, it implements: |
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55 | lower_mac/crc_simple.[ch] |
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56 | * CRC16-CCITT (currently defunct/broken as we need it for |
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57 | non-octet-aligned bitfields) |
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58 | lower_mac/tetra_conv_enc.[ch] |
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59 | * 16-state Rate-Compatible Punctured Convolutional (RCPC) coder |
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60 | lower_mac/tetra_interleave.[ch] |
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61 | * Block interleaving (over a single block only) |
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62 | lower_mac/tetra_rm3014.[ch] |
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63 | * (30, 14) Reed-Muller code for the ACCH (broadcast block of |
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64 | each downlink burst) |
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65 | lower_mac/tetra_scramb.[ch] |
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66 | * Scrambling |
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67 | lower_mac/viterbi*.[ch] |
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68 | * Convolutional decoder for signalling and voice channels |
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69 | phy/tetra_burst.[ch] |
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70 | * Routines to encode continuous normal and sync bursts |
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71 | phy/tetra_burst_sync.[ch] |
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72 | |||
73 | |||
74 | === Receiver Program === |
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75 | |||
76 | The main receiver program 'tetra-rx' expects an input file containing a |
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77 | stream of unpacked bits, i.e. 1-bit-per-byte. |
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78 | |||
79 | |||
80 | === Transmitter Program === |
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81 | |||
82 | The main program conv_enc_test.c generates a single continuous downlinc sync |
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83 | burst (SB), contining: |
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84 | * a SYNC-PDU as block 1 |
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85 | * a ACCESS-ASSIGN PDU as broadcast block |
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86 | * a SYSINFO-PDU as block 2 |
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87 | |||
88 | Scrambling is set to 0 (no scrambling) for all elements of the burst. |
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89 | |||
90 | It does not actually modulate and/or transmit yet. |
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91 | |||
92 | |||
93 | == Quick example == |
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94 | |||
95 | assuming you have generated a file samples.cfile at a sample rate of 195.312kHz (100MHz/512 == USRP2 at decimation 512) |
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96 | |||
97 | {{{ |
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98 | ./src/demod/python/tetra-demod.py -i /tmp/samples.cfile -o /tmp/out.float -s 195312 -c 0 |
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99 | ./src/float_to_bits /tmp/out.float /tmp/out.bits |
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100 | ./src/tetra-rx /tmp/out.bits |
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101 | }}} |
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102 | 1 | ||
103 | For a complete list of local wiki pages, see TitleIndex. |