Osmo-tetra » History » Version 21
laforge, 07/27/2023 08:30 PM
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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8 | |||
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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12 | |||
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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44 | |||
45 | 1 | laforge | The source code is available via read-only git access at |
46 | 15 | horiz0n | <pre> |
47 | 20 | laforge | git clone https://gitea.osmocom.org/tetra/osmo-tetra.git |
48 | 15 | horiz0n | </code></pre> |
49 | 1 | laforge | |
50 | 20 | laforge | You can also browse the source code at https://gitea.osmocom.org/tetra/osmo-tetra |
51 | 1 | laforge | |
52 | 20 | laforge | You will need [[libosmocore:]] to link against. |
53 | 1 | laforge | |
54 | 21 | laforge | h2. Mailing List / Forum |
55 | 15 | horiz0n | |
56 | 1 | laforge | There is a public mailing list regarding development of this project, you can |
57 | visit the subscription page at https://lists.osmocom.org/mailman/listinfo/tetra |
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58 | |||
59 | 2 | horiz0n | Please make sure to read the [[cellular-infrastructure:MailingListRules]] before posting. |
60 | 21 | laforge | |
61 | There's now also a "TETRA category in our discourse forum":https://discourse.osmocom.org/c/tetra |
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62 | 1 | laforge | |
63 | 15 | horiz0n | h2. FAQ |
64 | 1 | laforge | |
65 | 15 | horiz0n | We now have a [[FAQ]] (Frequently asked Questions) page! |
66 | 1 | laforge | |
67 | 15 | horiz0n | h2. Demodulator |
68 | 1 | laforge | |
69 | 18 | laforge | <pre> |
70 | src/demod/python/cpsk.py |
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71 | </pre> |
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72 | 1 | laforge | |
73 | 18 | laforge | * contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI |
74 | |||
75 | 1 | laforge | <pre> |
76 | 18 | laforge | src/demod/python/tetra-demod.py |
77 | </pre> |
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78 | |||
79 | * call demodulator on a 'cfile' containing complex baseband samples |
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80 | |||
81 | 1 | laforge | <pre> |
82 | 18 | laforge | src/demod/python/usrp1-tetra_demod.py |
83 | </pre> |
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84 | |||
85 | * use demodulator in realtime with a USRP1 SDR |
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86 | |||
87 | 1 | laforge | <pre> |
88 | 18 | laforge | src/demod/python/usrp2-tetra_demod.py |
89 | </pre> |
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90 | |||
91 | * use demodulator in realtime with a USRP2 SDR |
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92 | |||
93 | 1 | laforge | <pre> |
94 | 18 | laforge | src/demod/python/fcdp-tetra_demod.py |
95 | src/demod/python/fcdp-tetra_demod_fft.py |
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96 | </pre> |
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97 | 1 | laforge | |
98 | 18 | laforge | * 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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100 | 15 | horiz0n | The output of the demodulator is a file containing one float value for each symbol, |
101 | 1 | laforge | containing the phase shift (in units of pi/4) relative to the previous symbol. |
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103 | 18 | laforge | You can use the @float_to_bits@ program to convert the float values to unpacked bits, i.e. 1-bit-per-byte |
104 | 1 | laforge | |
105 | |||
106 | h2. PHY/MAC layer |
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107 | |||
108 | |||
109 | h3. library code |
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110 | |||
111 | |||
112 | Specifically, it implements: |
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113 | |||
114 | <pre> |
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115 | 18 | laforge | lower_mac/crc_simple.[ch] |
116 | </pre> |
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117 | |||
118 | * CRC16-CCITT (currently defunct/broken as we need it for non-octet-aligned bitfields) |
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119 | |||
120 | 1 | laforge | <pre> |
121 | 18 | laforge | lower_mac/tetra_conv_enc.[ch] |
122 | </pre> |
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123 | |||
124 | * 16-state Rate-Compatible Punctured Convolutional (RCPC) coder |
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125 | |||
126 | 1 | laforge | <pre> |
127 | 18 | laforge | lower_mac/tetra_interleave.[ch] |
128 | </pre> |
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129 | |||
130 | * Block interleaving (over a single block only) |
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131 | |||
132 | 1 | laforge | <pre> |
133 | 18 | laforge | lower_mac/tetra_rm3014.[ch] |
134 | </pre> |
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135 | |||
136 | * (30, 14) Reed-Muller code for the ACCH (broadcast block of each downlink burst) |
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137 | |||
138 | 1 | laforge | <pre> |
139 | 18 | laforge | lower_mac/tetra_scramb.[ch] |
140 | </pre> |
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141 | 1 | laforge | |
142 | 18 | laforge | * Scrambling |
143 | 1 | laforge | |
144 | 18 | laforge | <pre> |
145 | lower_mac/viterbi*.[ch] |
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146 | </pre> |
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147 | 15 | horiz0n | |
148 | 18 | laforge | * Convolutional decoder for signalling and voice channels |
149 | 1 | laforge | |
150 | 18 | laforge | <pre> |
151 | phy/tetra_burst.[ch] |
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152 | </pre> |
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153 | 15 | horiz0n | |
154 | 18 | laforge | * Routines to encode continuous normal and sync bursts |
155 | |||
156 | 1 | laforge | <pre> |
157 | 18 | laforge | phy/tetra_burst_sync.[ch] |
158 | </pre> |
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159 | 1 | laforge | |
160 | |||
161 | 18 | laforge | h3. Receiver Program |
162 | 3 | horiz0n | |
163 | 18 | laforge | The main receiver program @tetra-rx@ expects an input file containing a stream of unpacked bits, i.e. 1-bit-per-byte. |
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165 | 15 | horiz0n | h3. Transmitter Program |
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167 | 18 | laforge | The main program conv_enc_test.c generates a single continuous downlink sync burst (SB), containing: |
168 | * a SYNC-PDU as block 1 |
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169 | * a ACCESS-ASSIGN PDU as broadcast block |
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170 | * a SYSINFO-PDU as block 2 |
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171 | 5 | horiz0n | |
172 | 13 | horiz0n | Scrambling is set to 0 (no scrambling) for all elements of the burst. |
173 | 11 | horiz0n | |
174 | 15 | horiz0n | It does not actually modulate and/or transmit yet. |
175 | 1 | laforge | |
176 | 11 | horiz0n | |
177 | 14 | horiz0n | h2. Quick example |
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179 | 18 | laforge | assuming you have generated a file @samples.cfile@ at a sample rate of 195.312kHz (100MHz/512 == USRP2 at decimation 512) |
180 | 10 | horiz0n | |
181 | 6 | horiz0n | <pre> |
182 | 10 | horiz0n | ./src/demod/python/tetra-demod.py -i /tmp/samples.cfile -o /tmp/out.float -s 195312 -c 0 |
183 | 5 | horiz0n | ./src/float_to_bits /tmp/out.float /tmp/out.bits |
184 | 15 | horiz0n | ./src/tetra-rx /tmp/out.bits |
185 | 18 | laforge | </pre> |
186 | 1 | laforge | |
187 | Also, you may use pipes to glue the three programs running in different terminals together to achieve real time operation. |
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188 | 15 | horiz0n | |
189 | <pre> |
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190 | mkfifo /tmp/out.float |
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191 | mkfifo /tmp/out.bits |
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192 | ./src/demod/python/fcdp-tetra_demod.py -D hw:1,0 -o /tmp/out.float |
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193 | ... |
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194 | 18 | laforge | </pre> |
195 | 15 | horiz0n | |
196 | 17 | laforge | 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. |
197 | 1 | laforge | |
198 | * Adjust the center frequency (-f) and gain (-g) according to your needs. |
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199 | * Use left click in Wideband Spectrum window to roughly select a TETRA carrier. |
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200 | 15 | horiz0n | * In Wideband Spectrum you may also tune by 1/4 of the bandwidth at once by clicking on the rightmost/leftmost spectrum side. |
201 | 1 | laforge | * Use left click in Channel Spectrum window to fine tune the carrier by clicking on the left or right side of the spectrum. |
202 | 15 | horiz0n | |
203 | 1 | laforge | !osmo-tetra-demod.png! |
204 | |||
205 | For live capture call: |
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206 | |||
207 | <pre> |
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208 | 15 | horiz0n | src$ ./demod/python/osmosdr-tetra_demod_fft.py -o /dev/stdout | ./float_to_bits /dev/stdin /dev/stdout | ./tetra-rx /dev/stdin |
209 | 18 | laforge | </pre> |
210 | 15 | horiz0n | |
211 | 1 | laforge | You may specify gr-osmosdr device arguments by using the --args commandline option. |
212 | |||
213 | To use a gnuradio .cfile as input: |
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214 | |||
215 | <pre> |
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216 | 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 |
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217 | 18 | laforge | </pre> |
218 | 1 | laforge | |
219 | Note the mandatory rate argument and optional repeat & throttle arguments. |