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