# data rate cdma chirp

I combined a chirp with a CDMA and I would like to know how to find the data rate. To begin, I spread the datas with the chirp and after I spread the previous signal with the PN code.

My bandwidth is $$B$$, the PN length is $$L$$ and the chirp time is $$T_u$$. For me, the data rate (BPSK modulation) is $$D=\frac {1}{(L/B)T_u}$$. Is it correct?

• It's not clear how you "combined a chirp" with anything, can you please elaborate? – Marcus Müller May 5 '19 at 11:12
• you tried to edit your post as an anonymous user – would've been easier to just log in and add the To begin, I spread the datas with the chirp and after I spread the previous signal with the PN code. – Marcus Müller May 5 '19 at 12:23
• I see how you can spread something with a chirp, but how does one apply a PN sequence to a chirp? A chirp is an analogue wave form. My suspicion is that you apply the PN sequence to each sample of the chirp. That sounds counterintuitive – while there is technological advantage as having chirps "on the air", you'd break that by first chirping and then PN'ing the samples of that. The other way around would make much more sense – PN first, chirp after. I also think that's what LoRa does. – Marcus Müller May 5 '19 at 12:26
• Also, what you're doing looks like spreading, which does not increase the data rate, only the bandwidth. – MBaz May 5 '19 at 14:49