gct
Newbie level 1
I'm hoping someone can point me to a good resource on practical CPFSK receiver design. I understand the basics of the optimal receiver, but it's very computationally intensive. In particular I'm looking at building a software receiver for ETSI DMR. They use a 4-CPFSK with h=.27 I believe the pulse shaping function is 3 periods long, so I end up with a 12800 state trellis (ouch). I'm guessing someone's done better than that at this point, but haven't had any luck with the literature.
Additionally, if anyone knows, they apply a root-raised cosine to the frequency alphabet before generating the signal, to smooth out the phase profile. Generally when I see an RRC, I know I have to apply it at the receive too to minimize ISI. However, I'm not sure that applies here as we don't sample in the center of the symbol as with QPSK/BPSK, rather we have to apply a matched filter over the symbol interval, so I'm not 100% on what the benefit is.
Additionally, if anyone knows, they apply a root-raised cosine to the frequency alphabet before generating the signal, to smooth out the phase profile. Generally when I see an RRC, I know I have to apply it at the receive too to minimize ISI. However, I'm not sure that applies here as we don't sample in the center of the symbol as with QPSK/BPSK, rather we have to apply a matched filter over the symbol interval, so I'm not 100% on what the benefit is.