Osmo-tetra » History » Version 17
laforge, 02/21/2016 09:59 AM
1 | 15 | horiz0n | {{>toc}} |
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2 | 1 | laforge | |
3 | 15 | horiz0n | h1. Osmocom TETRA MAC/PHY layer experimentation code |
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6 | 1 | laforge | This code aims to implement the sending and receiving part of the |
7 | TETRA MAC/PHY layer. |
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9 | If you read the ETSI EN 300 392-2 (TETRA V+D Air Interface), you will |
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10 | find this code implementing the parts between the MAC-blocks (called |
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11 | type-1 bits) and the bits that go to the DQPSK-modulator (type-5 bits). |
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13 | It is most useful to look at Figure 8.5, 8.6, 9.3 and 19.12 of the |
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14 | abovementioned specification in conjunction with this program. |
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17 | 15 | horiz0n | h2. Big picture |
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20 | 16 | laforge | {{graphviz_link() |
21 | 1 | laforge | digraph G { |
22 | graph [ rankdir = LR ]; |
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23 | |||
24 | bits_file2 -> tetra_rx [ label = "read" ]; |
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25 | tetra_rx -> console [ label = "stdout" ]; |
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26 | tetra_rx -> wireshark [ label = "GSMTAP" ]; |
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27 | |||
28 | float_file2 -> float_to_bits [ label = "read" ]; |
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29 | float_to_bits -> bits_file1 [ label = "write" ]; |
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30 | |||
31 | USRP -> tetra_demod [ label = "USB" ]; |
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32 | tetra_demod -> float_file1 [ label = "write" ]; |
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33 | |||
34 | bits_file1 [ shape=box label="file.bits" ]; |
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35 | bits_file2 [ shape=box label="file.bits" ]; |
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36 | float_file1 [ shape=box label="file.float" ]; |
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37 | float_file2 [ shape=box label="file.float" ]; |
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38 | tetra_rx [ label="tetra-rx" ]; |
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39 | tetra_demod [ label="tetra-demod.py" ]; |
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40 | 15 | horiz0n | } |
41 | 16 | laforge | }} |
42 | 15 | horiz0n | |
43 | h2. Source Code |
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45 | 1 | laforge | The source code is available via read-only git access at |
46 | 15 | horiz0n | <pre> |
47 | 1 | laforge | git clone git://git.osmocom.org/osmo-tetra.git |
48 | 15 | horiz0n | </code></pre> |
49 | 1 | laforge | |
50 | You can also browse the source code at http://cgit.osmocom.org/ |
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51 | |||
52 | 15 | horiz0n | You will need "libosmocore":http://bb.osmocom.org/trac/wiki/libosmocore to link. |
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54 | 15 | horiz0n | |
55 | h2. Mailing List |
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57 | 1 | laforge | There is a public mailing list regarding development of this project, you can |
58 | visit the subscription page at https://lists.osmocom.org/mailman/listinfo/tetra |
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60 | 15 | horiz0n | This list is *for discussion between software developers* who intend to improve the |
61 | 1 | laforge | Osmocom TETRA software. It is not a forum for individuals asking how they can tap |
62 | 2 | horiz0n | into police radio (which is encrypted anyway). |
63 | 1 | laforge | |
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65 | 15 | horiz0n | h2. FAQ |
66 | 1 | laforge | |
67 | 15 | horiz0n | We now have a [[FAQ]] (Frequently asked Questions) page! |
68 | 1 | laforge | |
69 | 15 | horiz0n | |
70 | h2. Demodulator |
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73 | <pre> |
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74 | ******** contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI |
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75 | <pre> |
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76 | ******** call demodulator on a 'cfile' containing complex baseband samples |
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77 | <pre> |
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78 | ******** use demodulator in realtime with a USRP1 SDR |
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79 | <pre> |
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80 | ******** use demodulator in realtime with a USRP2 SDR |
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81 | <pre> |
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82 | <pre> |
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83 | ******** use demodulator in realtime with a [[Funcube_Dongle]]. Please use the "qthid":https://github.com/csete/qthid application to tune the dongle and adjust its gain/filter parameters for best reception result. This demodulator may also be used with other Softrock-type receivers by downconverting the intermediate frequency of a radio scanner to the complex baseband. |
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85 | 1 | laforge | The output of the demodulator is a file containing one float value for each symbol, |
86 | containing the phase shift (in units of pi/4) relative to the previous symbol. |
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88 | You can use the "float_to_bits" program to convert the float values to unpacked |
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89 | bits, i.e. 1-bit-per-byte |
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93 | 15 | horiz0n | h2. PHY/MAC layer |
94 | 1 | laforge | |
95 | 15 | horiz0n | |
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97 | h3. library code |
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100 | 1 | laforge | Specifically, it implements: |
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102 | 15 | horiz0n | <pre> |
103 | ******** CRC16-CCITT (currently defunct/broken as we need it for |
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104 | 1 | laforge | non-octet-aligned bitfields) |
105 | 15 | horiz0n | <pre> |
106 | ******** 16-state Rate-Compatible Punctured Convolutional (RCPC) coder |
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107 | <pre> |
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108 | ******** Block interleaving (over a single block only) |
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109 | <pre> |
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110 | ******** (30, 14) Reed-Muller code for the ACCH (broadcast block of |
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111 | 1 | laforge | each downlink burst) |
112 | 15 | horiz0n | <pre> |
113 | ******** Scrambling |
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114 | <pre> |
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115 | ******** Convolutional decoder for signalling and voice channels |
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116 | <pre> |
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117 | ******** Routines to encode continuous normal and sync bursts |
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118 | <pre> |
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119 | 1 | laforge | |
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122 | 15 | horiz0n | h3. Receiver Program |
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125 | <pre> |
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126 | 1 | laforge | stream of unpacked bits, i.e. 1-bit-per-byte. |
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130 | 15 | horiz0n | h3. Transmitter Program |
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133 | <pre> |
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134 | 1 | laforge | burst (SB), contining: |
135 | 15 | horiz0n | ******** a SYNC-PDU as block 1 |
136 | ******** a ACCESS-ASSIGN PDU as broadcast block |
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137 | ******** a SYSINFO-PDU as block 2 |
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138 | 1 | laforge | |
139 | Scrambling is set to 0 (no scrambling) for all elements of the burst. |
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141 | It does not actually modulate and/or transmit yet. |
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142 | 3 | horiz0n | |
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145 | 15 | horiz0n | h2. Quick example |
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148 | 3 | horiz0n | 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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150 | 15 | horiz0n | <pre> |
151 | 5 | horiz0n | ./src/demod/python/tetra-demod.py -i /tmp/samples.cfile -o /tmp/out.float -s 195312 -c 0 |
152 | 13 | horiz0n | ./src/float_to_bits /tmp/out.float /tmp/out.bits |
153 | 11 | horiz0n | ./src/tetra-rx /tmp/out.bits |
154 | 15 | horiz0n | </code></pre> |
155 | 11 | horiz0n | |
156 | 14 | horiz0n | Also, you may use pipes to glue the three programs running in different terminals together to achieve real time operation. |
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158 | 15 | horiz0n | <pre> |
159 | 10 | horiz0n | mkfifo /tmp/out.float |
160 | 6 | horiz0n | mkfifo /tmp/out.bits |
161 | 10 | horiz0n | ./src/demod/python/fcdp-tetra_demod.py -D hw:1,0 -o /tmp/out.float |
162 | 5 | horiz0n | ... |
163 | 15 | horiz0n | </code></pre> |
164 | 5 | horiz0n | |
165 | 1 | laforge | |
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167 | 15 | horiz0n | |
168 | The most user friendly way is the script osmosdr-tetra_demod_fft.py which is based on "gr-osmosdr":http://sdr.osmocom.org/trac/wiki/GrOsmoSDR and supports various radio hardware (OsmoSDR, RTLSDR, FCD, UHD) as well as IQ file input. |
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170 | * Adjust the center frequency (-f) and gain (-g) according to your needs. |
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171 | * Use left click in Wideband Spectrum window to roughly select a TETRA carrier. |
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172 | * In Wideband Spectrum you may also tune by 1/4 of the bandwidth at once by clicking on the rightmost/leftmost spectrum side. |
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173 | * Use left click in Channel Spectrum window to fine tune the carrier by clicking on the left or right side of the spectrum. |
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174 | |||
175 | 17 | laforge | !osmo-tetra-demod.png! |
176 | 1 | laforge | |
177 | For live capture call: |
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179 | 15 | horiz0n | <pre> |
180 | 1 | laforge | src$ ./demod/python/osmosdr-tetra_demod_fft.py -o /dev/stdout | ./float_to_bits /dev/stdin /dev/stdout | ./tetra-rx /dev/stdin |
181 | 15 | horiz0n | </code></pre> |
182 | 1 | laforge | |
183 | You may specify gr-osmosdr device arguments by using the --args commandline option. |
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184 | |||
185 | To use a gnuradio .cfile as input: |
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187 | 15 | horiz0n | <pre> |
188 | 1 | laforge | src$ ./demod/python/osmosdr-tetra_demod_fft.py -a "file=/path/to/tetra_sps1024e3.cfile,rate=1024e3,repeat=true,throttle=true" -o /dev/stdout | ./float_to_bits /dev/stdin /dev/stdout | ./tetra-rx /dev/stdin |
189 | 15 | horiz0n | </code></pre> |
190 | 1 | laforge | |
191 | Note the mandatory rate argument and optional repeat & throttle arguments. |