Osmo-tetra » History » Revision 15
Revision 14 (horiz0n, 02/19/2016 10:52 PM) → Revision 15/21 (horiz0n, 02/19/2016 10:52 PM)
{{>toc}} h1. [[PageOutline]] = 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. h2. == Big picture <pre> <code class="graphviz"> == {{{ #!graphviz digraph G { graph [ rankdir = LR ]; bits_file2 -> tetra_rx [ label = "read" ]; tetra_rx -> console [ label = "stdout" ]; tetra_rx -> wireshark [ label = "GSMTAP" ]; float_file2 -> float_to_bits [ label = "read" ]; float_to_bits -> bits_file1 [ label = "write" ]; USRP -> tetra_demod [ label = "USB" ]; tetra_demod -> float_file1 [ label = "write" ]; bits_file1 [ shape=box label="file.bits" ]; bits_file2 [ shape=box label="file.bits" ]; float_file1 [ shape=box label="file.float" ]; float_file2 [ shape=box label="file.float" ]; tetra_rx [ label="tetra-rx" ]; tetra_demod [ label="tetra-demod.py" ]; } </code></pre> h2. }}} == Source Code == The source code is available via read-only git access at <pre> {{{ git clone git://git.osmocom.org/osmo-tetra.git </code></pre> }}} You can also browse the source code at http://cgit.osmocom.org/ You will need "libosmocore":http://bb.osmocom.org/trac/wiki/libosmocore [http://bb.osmocom.org/trac/wiki/libosmocore libosmocore] to link. h2. == 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 '''for discussion between software developers* 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). h2. == FAQ == We now have a [[FAQ]] [wiki:FAQ] (Frequently asked Questions) page! h2. == Demodulator <pre> ******** == {{{src/demod/python/cpsk.py}}} * contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI <pre> ******** {{{src/demod/python/tetra-demod.py}}} * call demodulator on a 'cfile' containing complex baseband samples <pre> ******** {{{src/demod/python/usrp1-tetra_demod.py}}} * use demodulator in realtime with a USRP1 SDR <pre> ******** {{{src/demod/python/usrp2-tetra_demod.py}}} * use demodulator in realtime with a USRP2 SDR <pre> <pre> ******** {{{src/demod/python/fcdp-tetra_demod.py}}} {{{src/demod/python/fcdp-tetra_demod_fft.py}}} * use demodulator in realtime with a [[Funcube_Dongle]]. [wiki:Funcube_Dongle]. Please use the "qthid":https://github.com/csete/qthid [https://github.com/csete/qthid 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> ******** {{{lower_mac/crc_simple.[ch]}}} * CRC16-CCITT (currently defunct/broken as we need it for non-octet-aligned bitfields) <pre> ******** {{{lower_mac/tetra_conv_enc.[ch]}}} * 16-state Rate-Compatible Punctured Convolutional (RCPC) coder <pre> ******** {{{lower_mac/tetra_interleave.[ch]}}} * Block interleaving (over a single block only) <pre> ******** {{{lower_mac/tetra_rm3014.[ch]}}} * (30, 14) Reed-Muller code for the ACCH (broadcast block of each downlink burst) <pre> ******** {{{lower_mac/tetra_scramb.[ch]}}} * Scrambling <pre> ******** {{{lower_mac/viterbi*.[ch]}}} * Convolutional decoder for signalling and voice channels <pre> ******** {{{phy/tetra_burst.[ch]}}} * Routines to encode continuous normal and sync bursts <pre> h3. {{{phy/tetra_burst_sync.[ch]}}} === Receiver Program <pre> === The main receiver program {{{tetra-rx}}} expects an input file containing a stream of unpacked bits, i.e. 1-bit-per-byte. h3. === Transmitter Program <pre> === The main program {{{conv_enc_test.c}}} generates a single continuous downlink sync 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> }}} [[BR]][[BR]] 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 [http://sdr.osmocom.org/trac/wiki/GrOsmoSDR gr-osmosdr] 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.
