TETRA MAC/PHY layer experimentation code

(C) 2010-2016 by Harald Welte laforge@gnumonks.org and contributors

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 libosmocore (http://bb.osmocom.org/trac/wiki/libosmocore) to link.

Demodulator

src/demod/python/cpsk.py

• contains a gnuradio based pi4/DQPSK demodulator, courtesy of KA1RBI

src/demod/python/osmosdr-tetra_demod_fft.py

• call demodulator on any source supported by gr-osmosdr (uhd, fcd, hackrf, blaerf, etc.)

src/demod/python/simdemod2.py

• call demodulator on a 'cfile' containing complex baseband samples

src/demod/python/{uhd,fcdp}-tetra_demod.py

• use demodulator directly with UHd or FCDP hadware (no gr-osmosdr)

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

PHY/MAC layer

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 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
src/tetra-rx /tmp/out.bits