Hi,
I've started to implement the TETRA TMO MAC layer, i.e. the part that takes
MAC blocks from higher layers and applies CRC, FEC, interleaving and scrambling
before finally handing the bits to the DQPSK-modulator.
The code can now generate a (hopefully valid) to-be-modulated bit pattern
for a 'continuous downlink synchronization burst', i.e. what corresponds to
the 'SCH+FCCH+BCCH' in GSM.
You can find the code (including a small README) at:
gitosis@git.osmocom.org:tetra-misc.git
in the 'src' directory.
If you don't yet have git access, feel free to mail me your sshv2 key.
What's missing:
* CRC16-CCITT to be computed over odd number of bits like 60 or 124
(all common implementations assume you encode integral # of bytes) [zecke]
* decoding:
* decoder for the RM(30,14) code [zecke]
* soft-input/soft-decision viterbi for the RCPC code
* synchronizer, able to detect synchro and normal training sequence [laforge]
Once those tasks are completed, we can not only generate simulated burst bit
patterns, but also decode them - which should be a good start for the time
when Hopscotch' demodulator will spit out some real received bitstream.
Regards,
Harald
--
- Harald Welte <laforge(a)gnumonks.org> http://laforge.gnumonks.org/
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