I’ve only learned about this through my engineering studies, so I can only really recommend textbooks. I found Proakis’ Digital Communication quite good, but it doesn’t go very deep.

I don’t know of any online resources – but I’d love to have the time to write some signal processing for communication is fascinating and has a wide impact on everyday life.

Also wrt. implementations: I think GNU Radio might be a good place to look, but honestly the actual implementation of these algorithms is often very simple, it is the theory behind them that gets hairy.