OsmocomTETRA » History » Version 6
laforge, 02/19/2016 10:52 PM
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1 | 6 | laforge | [[PageOutline]] |
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2 | 2 | laforge | = Osmocom TETRA MAC/PHY layer experimentation code = |
3 | 1 | ||
4 | 2 | laforge | This code aims to implement the sending and receiving part of the |
5 | TETRA MAC/PHY layer. |
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7 | 2 | laforge | If you read the ETSI EN 300 392-2 (TETRA V+D Air Interface), you will |
8 | find this code implementing the parts between the MAC-blocks (called |
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9 | type-1 bits) and the bits that go to the DQPSK-modulator (type-5 bits). |
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11 | 3 | laforge | It is most useful to look at Figure 8.5, 8.6, 9.3 and 19.12 of the |
12 | abovementioned specification in conjunction with this program. |
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14 | 3 | laforge | |
15 | == Source Code == |
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16 | The source code is available via read-only git access at |
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17 | {{{ |
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18 | git clone git://git.osmocom.org/osmo-tetra.git |
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19 | }}} |
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20 | |||
21 | 5 | laforge | You can also browse the source code at http://cgit.osmocom.org/ |
22 | 3 | laforge | |
23 | 1 | You will need [http://bb.osmocom.org/trac/wiki/libosmocore libosmocore] to link. |
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24 | 3 | laforge | |
25 | == Mailing List == |
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26 | There is a public mailing list regarding development of this project, you can |
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27 | visit the subscription page at https://lists.osmocom.org/mailman/listinfo/tetra |
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28 | |||
29 | This list is '''for discussion between software developers''' who intend to improve the |
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30 | Osmocom TETRA software. It is not a forum for individuals asking how they can tap |
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31 | into police radio (which is encrypted anyway). |
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32 | 6 | laforge | |
33 | == FAQ == |
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34 | We now have a [wiki:FAQ] (Frequently asked Questions) page! |
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36 | 2 | laforge | == Demodulator == |
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38 | 2 | laforge | src/demod/python/cpsk.py |
39 | * contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI |
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40 | src/demod/python/tetra-demod.py |
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41 | * call demodulator on a 'cfile' containing complex baseband samples |
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42 | src/demod/python/usrp1-tetra_demod.py |
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43 | * use demodulator in realtime with a USRP1 SDR |
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44 | src/demod/python/usrp2-tetra_demod.py |
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45 | * use demodulator in realtime with a USRP2 SDR |
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46 | 1 | ||
47 | 2 | laforge | The output of the demodulator is a file containing one float value for each symbol, |
48 | containing the phase shift (in units of pi/4) relative to the previous symbol. |
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50 | 2 | laforge | You can use the "float_to_bits" program to convert the float values to unpacked |
51 | bits, i.e. 1-bit-per-byte |
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52 | 1 | ||
53 | |||
54 | 2 | laforge | == PHY/MAC layer == |
55 | |||
56 | === library code === |
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57 | |||
58 | Specifically, it implements: |
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59 | lower_mac/crc_simple.[ch] |
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60 | * CRC16-CCITT (currently defunct/broken as we need it for |
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61 | non-octet-aligned bitfields) |
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62 | lower_mac/tetra_conv_enc.[ch] |
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63 | * 16-state Rate-Compatible Punctured Convolutional (RCPC) coder |
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64 | lower_mac/tetra_interleave.[ch] |
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65 | * Block interleaving (over a single block only) |
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66 | lower_mac/tetra_rm3014.[ch] |
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67 | * (30, 14) Reed-Muller code for the ACCH (broadcast block of |
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68 | each downlink burst) |
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69 | lower_mac/tetra_scramb.[ch] |
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70 | * Scrambling |
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71 | lower_mac/viterbi*.[ch] |
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72 | * Convolutional decoder for signalling and voice channels |
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73 | phy/tetra_burst.[ch] |
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74 | * Routines to encode continuous normal and sync bursts |
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75 | phy/tetra_burst_sync.[ch] |
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76 | |||
77 | |||
78 | === Receiver Program === |
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79 | |||
80 | The main receiver program 'tetra-rx' expects an input file containing a |
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81 | stream of unpacked bits, i.e. 1-bit-per-byte. |
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82 | |||
83 | |||
84 | === Transmitter Program === |
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85 | |||
86 | The main program conv_enc_test.c generates a single continuous downlinc sync |
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87 | burst (SB), contining: |
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88 | * a SYNC-PDU as block 1 |
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89 | * a ACCESS-ASSIGN PDU as broadcast block |
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90 | * a SYSINFO-PDU as block 2 |
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91 | |||
92 | Scrambling is set to 0 (no scrambling) for all elements of the burst. |
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93 | |||
94 | It does not actually modulate and/or transmit yet. |
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95 | |||
96 | |||
97 | == Quick example == |
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98 | |||
99 | 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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100 | |||
101 | {{{ |
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102 | ./src/demod/python/tetra-demod.py -i /tmp/samples.cfile -o /tmp/out.float -s 195312 -c 0 |
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103 | ./src/float_to_bits /tmp/out.float /tmp/out.bits |
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104 | ./src/tetra-rx /tmp/out.bits |
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105 | }}} |
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106 | 1 | ||
107 | For a complete list of local wiki pages, see TitleIndex. |