Chipset Supports direct access to I/Q samples

[Lynn Zhou]

Hello expert,

I just jump from TI. Could anyone tell me if nordic has any chipset like TI CC1310 which supports direct access to the receiver I/Q quadrature samples?

Thank you so much!
Lynn Z

[Andreas]

Hi,

 

Not for the whole packet, but using the 'Direction Finding' feature in some select nRF52 parts and nRF5340 you can sample the I and Q components of the appended CTE.

 

Best regards,

Andreas

[Lynn Zhou]

Hello Andreas,

I would like to work directly on the baseband I/Q samples and design my own demodulation methods. Similar to this question https://devzone.nordicsemi.com/f/nordic-q-a/41165/extracting-i-q-samples-from-ble-signals

I'm new to nRF. Could you share me a link or a doc which I could follow?

Thank you so much!

Lynn

[Dmitry]

Hi,

You can access I/Q data of the bitstream starting after an access address at 1M and 2M phys (see DFEINEXTENSION field in nRF52811 product spec). If you would like to decode the whole packet that's modulated differently from 1M/2M GFSK, you need to place a short GFSK packet with a known access address ahead of it, then you can capture up to 1 msec of bitstream as it would be CTE. There are no (reliable) methods to capture raw ADC output without access address match.

[Lynn Zhou]

Hi Dmitry,

Thanks for the information. What do you mean by reliable methods to work directly on the ADC raw I/Q output stream? Does nRF52811 have an API function which I could do partial read or check on the stream without checking the packet header? 

Theoretically, this process (demodulate baseband signal) would be needed to decode the packet. Am I right?

Thanks,

Lynn Z

[Dmitry]

When radio in in RX mode, RF signal is demodulated and decoded continuously, and internal logic performs a matching of the bitstream coming from decoder against configured access address (that can be 2 to 5 bytes long). When matching bytes are found, EDMA starts to write the rest of the decoded bitstream to your packet buffer. Also direction finding engine (with its own EDMA that writes I/Q samples into another buffer) can be started at this moment. You cannot force to start DFE when you need, you have to wait  for correct packet header coming from air.