Hi,
Thanks for the add, I have been hinted this place, and im looking forward to digging deeper into the realm of TETRA / DQPSK.
What im trying to do is write a C# program for demodulation of TETRA. and have come so far as to be able to view the IQ vector run around on the unity circle, but it appears a bit distorted. I think its due to a crude low pass filter i used on the I/Q signal causing this. From reading books and sites i find that I should probably used a raised cosine filter to keep the signal form beeing distorted (ISI). am i correct in my assumption? and do you have the open source code i can inspect, regardless if programming language.
I know there is tons of programs out there that can decode and even produce audio from TETRA DQPSK signals, and I have one installed, but i want to have an edge to this, i need to understand and learn first hand. It may take time, but thats how it is.
I have what is required regarding programming skills and radio knowledge - I am radio Amateur, and 20 years ago i did have Digital communication classes at Engineering college - But thats 20 years ago, and the equations in the books are kind of far away in my head.. but the theory sticks.
Please help me get up to speed in decoding DQPSK, im not expecting to do this quickly, but will be in steps when i have time, and will lead to questions. But at some point i could be on your frontier digging into TETRA as a whole.
Best Regards Kim Mortensen
Hi Kim,
On Sat, Feb 15, 2020 at 09:33:49AM +0100, Kim Mortensen wrote:
From reading books and sites i find that I should probably used a raised cosine filter to keep the signal form beeing distorted (ISI). am i correct in my assumption?
I'm not the expert on this subject, but RRC filters are used in a lot of receivers for (at least) GMSK or DQPSK, including the osmo-tetra implementation.
and do you have the open source code i can inspect, regardless if programming language.
osmoocm-tetra includes a Pi/4 DQPSK demodulator, you can find it in osmo-tetra.git at src/demod/cqpsk.py. It uses the root-raised-cosine filter provided by gnuradio.
In general, we would of course appreciate if you could contribute to the osmo-tetra implementation, rather than creating another implementation of something that already works in osmo-tetra. But it's of course your time and your call how you want to spend it :)
However, if you have your C# demodulator in a working stage, you could integrate it with the phy/mac implementation of osmo-tetra by generating the same soft-bit input file format that 'tetra-rx' consumes.
Regards, Harald
Hi,
Would someone happened to have a sample file containing I/Q data from a DQPSK signal. The content is not important, as long as its DQPSK - Preferably in wav format.
Best Regards Kim Mortensen
Den lør. 15. feb. 2020 kl. 09.33 skrev Kim Mortensen kimfmx@gmail.com:
Hi,
Thanks for the add, I have been hinted this place, and im looking forward to digging deeper into the realm of TETRA / DQPSK.
What im trying to do is write a C# program for demodulation of TETRA. and have come so far as to be able to view the IQ vector run around on the unity circle, but it appears a bit distorted. I think its due to a crude low pass filter i used on the I/Q signal causing this. From reading books and sites i find that I should probably used a raised cosine filter to keep the signal form beeing distorted (ISI). am i correct in my assumption? and do you have the open source code i can inspect, regardless if programming language.
I know there is tons of programs out there that can decode and even produce audio from TETRA DQPSK signals, and I have one installed, but i want to have an edge to this, i need to understand and learn first hand. It may take time, but thats how it is.
I have what is required regarding programming skills and radio knowledge - I am radio Amateur, and 20 years ago i did have Digital communication classes at Engineering college - But thats 20 years ago, and the equations in the books are kind of far away in my head.. but the theory sticks.
Please help me get up to speed in decoding DQPSK, im not expecting to do this quickly, but will be in steps when i have time, and will lead to questions. But at some point i could be on your frontier digging into TETRA as a whole.
Best Regards Kim Mortensen
-
Harald Welte -
Kim Mortensen