OsmocomTETRA » History » Version 2
= 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 in conjunction
with this program.
You will need [http://bb.osmocom.org/trac/wiki/libosmocore libosmocore] to link.Demodulator
* 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
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
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
=== 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 example
assuming 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
For a complete list of local wiki pages, see TitleIndex.