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OsmocomTETRA » History » Revision 4

Revision 3 (laforge, 02/19/2016 10:52 PM) → Revision 4/23 (laforge, 02/19/2016 10:52 PM)

= 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. 


 == 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 nttp://cgit.osmocom.org/ git://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). 

 == 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 
 }}} 

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