OsmocomTETRA

[[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.

== Big picture ==

{{{

#!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 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 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).

== FAQ ==

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

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

}}}

For a complete list of local wiki pages, see TitleIndex.