> I know very little about RFID, but I can make these observations on > how I would probably perform a naive demodulation of this signal.
> 1. Tune the USRP to your carrier frequency and bring your signal > down to baseband (centered around DC). > 2. Choose an appropriate number of samples per symbol or bit (I'd > arbitrarily choose 6 .. or 8). > 3. Filter the incoming signal to some appropriate spectral mask. > 4. Find the magnitude (or even power since it saves a sqrt) of the > complex vector. > 5. Develop some algorithm which accounts for frequency offset/tracking. > 6. Perform hard decisions from the soft decisions you make from the > algorithm developed in step (5). Marco, Are you trying to decode the reader transmission, or the tag reply? You may be able to use a matched filter as a first step to clean up the signal before demodulating. I'm not really sure what 13.56 MHz RFID signals look like, but that helps a lot at 915 MHz. Regardless, I think step 3 is the key to get you started. You don't want to just throw out the I or Q channel. You probably want to use the complex_to_mag block, and then the signal will look like what you expect. michael
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