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horiz0n, 02/19/2016 10:52 PM
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.
{{{
#!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" ];
}
}}}
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 [http://bb.osmocom.org/trac/wiki/libosmocore libosmocore] to link.
Mailing ListThere 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).
We now have a [wiki:FAQ] (Frequently asked Questions) page! Demodulator
src/demod/python/cpsk.py
* contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI
src/demod/python/tetra-demod.py
* call demodulator on a 'cfile' containing complex baseband samples
src/demod/python/usrp1-tetra_demod.py
* use demodulator in realtime with a USRP1 SDR
src/demod/python/usrp2-tetra_demod.py
* use demodulator in realtime with a USRP2 SDR
src/demod/python/fcdp-tetra_demod.py
* use demodulator in realtime with a [http://www.funcubedongle.com/ FUNcube Dongle Pro]. This 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
=== library code ===
Specifically, it implements:
lower_mac/crc_simple.[ch]
* CRC16-CCITT (currently defunct/broken as we need it for
non-octet-aligned bitfields)
lower_mac/tetra_conv_enc.[ch]
* 16-state Rate-Compatible Punctured Convolutional (RCPC) coder
lower_mac/tetra_interleave.[ch]
* Block interleaving (over a single block only)
lower_mac/tetra_rm3014.[ch]
* (30, 14) Reed-Muller code for the ACCH (broadcast block of
each downlink burst)
lower_mac/tetra_scramb.[ch]
* Scrambling
lower_mac/viterbi*.[ch]
* Convolutional decoder for signalling and voice channels
phy/tetra_burst.[ch]
* Routines to encode continuous normal and sync bursts
phy/tetra_burst_sync.[ch]
=== Receiver Program ===
The main receiver program 'tetra-rx' expects an input file containing a
stream of unpacked bits, i.e. 1-bit-per-byte.
=== Transmitter Program ===
The main program conv_enc_test.c generates a single continuous downlinc 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.
Quick exampleassuming you have generated a file samples.cfile at a sample rate of 195.312kHz (100MHz/512 == USRP2 at decimation 512)
{{{
./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
}}}
For a complete list of local wiki pages, see TitleIndex.
Updated by horiz0n about 8 years ago · 8 revisions