TETRA MAC/PHY layer experimentation code

(C) 2010-2016 by Harald Welte [email protected] 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 to build this softwar

Homepage

The official homepage of the project is https://osmocom.org/projects/tetra/wiki/OsmocomTETRA

GIT Repository

You can clone from the official osmo-tetra.git repository using

git clone https://gitea.osmocom.org/tetra/osmo-tetra

There is a web interface at https://gitea.osmocom.org/tetra/osmo-tetra

Mailing List

Discussions related to osmo-tetra are happening on the [email protected] mailing list, please see https://lists.osmocom.org/mailman/listinfo/tetra for subscription options and the list archive.

Please observe the Osmocom Mailing List Rules when posting.

Contributing

Our coding standards are described at https://osmocom.org/projects/cellular-infrastructure/wiki/Coding_standards

We us a gerrit based patch submission/review process for managing contributions. Please see https://osmocom.org/projects/cellular-infrastructure/wiki/Gerrit for more details

The current patch queue for osmo-tetra can be seen at https://gerrit.osmocom.org/#/q/project:osmo-tetra+status:open

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