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Re: [Discuss-gnuradio] Re: FSK4 Demodulation on the FPGA

From: Kevin Xu
Subject: Re: [Discuss-gnuradio] Re: FSK4 Demodulation on the FPGA
Date: Wed, 08 Dec 2010 16:50:15 -0500
User-agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv: Gecko/20101027 Thunderbird/3.1.6


Thanks so much for your quick response. As it turns out, I'm already part of the op25 yahoo group, and I've seen the good work the op25 group has done. However, like you said, I am looking for an implementation that's entirely USRP based. I am only looking to be able to get the demodulated symbols on the USRP rather than doing it on the PC. Would I need to implement all of the blocks you mentioned -

 - channel selection, downconversion to zero IF
 - decimation
 - FM demod
 - post-demod filtering (i.e., RRC filter)

- to accomplish this?


On 12/8/2010 9:11 AM, ikjtel wrote:
Hey all,
Has anyone attempted to implement a C4FM demodulator on the Altera
Cyclone in the USRP1? Right now I'm hoping to do this to read
P25 encrypted packets on the FPGA instead of on the CPU, and I
wanted to know if it was possible. If so, could anyone could
point me to any sort of examples or tutorials I could learn
from to accomplish this? It would be greatly appreciated.

We've got this working - although at present the code runs in the PC as a GNU 
Radio application.

Assuming you want a receiver implementation that's entirely USRP based, you 
would also need some other blocks in addition to the C4FM demod block -
  - channel selection, downconversion to zero IF
  - decimation
  - FM demod
  - post-demod filtering (i.e., RRC filter)

No idea if there is sufficient gate array capacity in the FPGA to implement all 
this, or not.

Anyway, here are a few links to get you started
  - http://sites.google.com/site/radiorausch/
  - http://sedition.org.au/op25/
  - op25-dev yahoogroup
The RadioRausch pages do not load properly for me.  Nonetheless, you want to go to the 
"four level FSK" page.

You would be most welcome to join the op25-dev group also.

Best of luck


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