IQ Sampling AoD

[ChristineA]

I am experimenting with sampling IQ at the payload in AoD mode. Are there any differences in the configuration of the receiver in AoA mode as seen in the direction finding whitepaper to the configuration of the receiver in AoD mode?

I followed the procedures in the whitepaper except for the CTEINLINECONF and antenna switching as I'll sample IQ from advertisement packets with no CTEInfo (and no CTE) and use only one antenna. However, when I check DFEPACKET.AMOUNT, I get 0 samples for each packet. Did I miss anything to actually start IQ sampling?

[Simonr]

Hi

Are you using the Direction Finding sample projects for reference on your end or making an implementation yourself? In the sample projects we have documentation on what changes are necessary to use Angle of departure mode:

• https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/bluetooth/direction_finding_connectionless_tx/README.html#angle_of_departure_mode 
• https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/bluetooth/direction_finding_connectionless_rx/README.html#angle_of_departure_mode 

I also see you say you're doing IQ sampling in the payload. Note that the CTE and IQ sampling is appended to the packet , after the CRC and is an offset unmodulated carrier, not an actual part of the payload. The payload only lets the receiver know that CTEInfo is coming after the CRC. More on that in the Direction Finding whitepaper. 

Best regards,

Simon

[ChristineA]

I am making an implementation different to the direction finding sample projects. As far as I have read on the PS and various tickets in DevZone, it is also possible to sample IQ in the payload by setting the DFEINEXTENSION bit to 0.

However, in my current implementation, I have mixed register level initialization of registers pertinent to IQ sampling and zephyr implementation of BLE to scan for packets. Is it not possible to do that? Do I have to use a proprietary mode to sample IQ in the payload?

[Simonr]

Hi

Okay, I see. It should be possible to do IQ sampling within the payload, but we don't have libraries/solutions doin this, so you will be on your own with in-payload DFE I'm afraid. All necessary information should be covered in the Direction Finding and radio sections of the nRF52833 product specification. Some important notes to this approach:

• You should be able to check resulting timing by checking the antenna switch pattern
• AGC is normally disabled, but for in-payload DFE this will always be active
• The sampling will be related to the ADDRESS event and you will need to calculate the delay you want from this point in the packet yourself.

Best regards,

Simon