We are maintaining a long list with theory/math: https://brmlab.cz/event/dsp#zdroje , and engineering stuff: https://brmlab.cz/project/sdr/start#links . However, I agree it is rather difficult to get into the topic. I'm playing with SDRs for almost 10 years (increasingly "fulltime" lately), and we still need to employ a professional mathematician to help me with some advanced problems.
https://www.dsprelated.com/showarticle/192.php https://www.katjaas.nl/home/home.html
We are maintaining a long list with theory/math: https://brmlab.cz/event/dsp#zdroje , and engineering stuff: https://brmlab.cz/project/sdr/start#links . However, I agree it is rather difficult to get into the topic. I'm playing with SDRs for almost 10 years (increasingly "fulltime" lately), and we still need to employ a professional mathematician to help me with some advanced problems.