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laforge, 02/21/2016 08:01 AM
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- Osmocom TETRA MAC/PHY layer experimentation code
Osmocom TETRA MAC/PHY layer experimentation code¶
This code aims to implement the sending and receiving part of the
TETRA MAC/PHY layer.
If you read the ETSI EN 300 392-2 (TETRA V+D Air Interface), you will
find this code implementing the parts between the MAC-blocks (called
type-1 bits) and the bits that go to the DQPSK-modulator (type-5 bits).
It is most useful to look at Figure 8.5, 8.6, 9.3 and 19.12 of the
abovementioned specification in conjunction with this program.
Big picture¶
Source Code¶
The source code is available via read-only git access at
git clone git://git.osmocom.org/osmo-tetra.git
You can also browse the source code at http://cgit.osmocom.org/
You will need libosmocore to link.
Mailing List¶
There is a public mailing list regarding development of this project, you can
visit the subscription page at https://lists.osmocom.org/mailman/listinfo/tetra
This list is for discussion between software developers who intend to improve the
Osmocom TETRA software. It is not a forum for individuals asking how they can tap
into police radio (which is encrypted anyway).
FAQ¶
We now have a FAQ (Frequently asked Questions) page!
Demodulator¶
******** contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI <pre> ******** call demodulator on a 'cfile' containing complex baseband samples <pre> ******** use demodulator in realtime with a USRP1 SDR <pre> ******** use demodulator in realtime with a USRP2 SDR <pre> <pre> ******** 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. The output of the demodulator is a file containing one float value for each symbol, containing the phase shift (in units of pi/4) relative to the previous symbol. You can use the "float_to_bits" program to convert the float values to unpacked bits, i.e. 1-bit-per-byte h2. PHY/MAC layer h3. library code Specifically, it implements: <pre> ******** CRC16-CCITT (currently defunct/broken as we need it for non-octet-aligned bitfields) <pre> ******** 16-state Rate-Compatible Punctured Convolutional (RCPC) coder <pre> ******** Block interleaving (over a single block only) <pre> ******** (30, 14) Reed-Muller code for the ACCH (broadcast block of each downlink burst) <pre> ******** Scrambling <pre> ******** Convolutional decoder for signalling and voice channels <pre> ******** Routines to encode continuous normal and sync bursts <pre> h3. Receiver Program <pre> stream of unpacked bits, i.e. 1-bit-per-byte. h3. Transmitter Program <pre> burst (SB), contining: ******** a SYNC-PDU as block 1 ******** a ACCESS-ASSIGN PDU as broadcast block ******** a SYSINFO-PDU as block 2 Scrambling is set to 0 (no scrambling) for all elements of the burst. It does not actually modulate and/or transmit yet. h2. Quick example assuming you have generated a file samples.cfile at a sample rate of 195.312kHz (100MHz/512 == USRP2 at decimation 512) <pre> ./src/demod/python/tetra-demod.py -i /tmp/samples.cfile -o /tmp/out.float -s 195312 -c 0 ./src/float_to_bits /tmp/out.float /tmp/out.bits ./src/tetra-rx /tmp/out.bits </code></pre> Also, you may use pipes to glue the three programs running in different terminals together to achieve real time operation. <pre> mkfifo /tmp/out.float mkfifo /tmp/out.bits ./src/demod/python/fcdp-tetra_demod.py -D hw:1,0 -o /tmp/out.float ... </code></pre> 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. * Adjust the center frequency (-f) and gain (-g) according to your needs. * Use left click in Wideband Spectrum window to roughly select a TETRA carrier. * In Wideband Spectrum you may also tune by 1/4 of the bandwidth at once by clicking on the rightmost/leftmost spectrum side. * Use left click in Channel Spectrum window to fine tune the carrier by clicking on the left or right side of the spectrum. [[Image(osmo-tetra-demod.png,25%)]] For live capture call: <pre> src$ ./demod/python/osmosdr-tetra_demod_fft.py -o /dev/stdout | ./float_to_bits /dev/stdin /dev/stdout | ./tetra-rx /dev/stdin </code></pre> You may specify gr-osmosdr device arguments by using the --args commandline option. To use a gnuradio .cfile as input: <pre> 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 </code></pre> Note the mandatory rate argument and optional repeat & throttle arguments.
Updated by laforge about 8 years ago · 16 revisions