Re: [Discuss-gnuradio] TETRA demodulator advices

Le lun. 7 déc. 2015 à 8:06, Sylvain Munaut <246tnt@gmail.com> a écrit :

Hi,

I've looked into that but I'm afraid some blocks won't play well with the constellation class (for example, they expect a constellation to have 2**(bits) points, but PI/4 DQPSK uses 2 bits and has 8 points). I think I will stay with the flowgraph approach for now.

I've worked with pi/4 xQPSK signals a bit when doing tetra and gmr stuff and the approach I took is just to undo the pi/4 rotation using a complex rotator. Then it looks like normal QPSK and can be processed as such. Cheers, Sylvain

Hi Sylvain,

I followed your suggestion and modified the PSK (De)Mod blocks, and the generic_(de)mod classes to add an optionnal rotation parameter, and a Rotator block if needed, and it works great !

It also seems to be more tolerant to noisy channels.

GNU radio maintainers : should I create a pull request to add the rotation parameter ? It would allow to have only one block for PI/4 QPSK (or PI/2 BPSK) demodulation.

Best,

Timothée.