Meaning of IQ remote and local (remote_pct and local_pct) in CS code (Does reflector actually match phase with Initiator?)

[Ar K]

In the cs_de.c, we have an IQ pair extracted from remote_pct and local_pct.

Assuming this code runs on initiator (where the ranging is done), and remote/local stands for reflector and initiator,
1) Is the remote IQ measured at reflector and sent in some other data packet towards initiator

OR

2)The reflector actually matches its response to exactly phase align with the tone received from initiator. 
(Acting as a true reflector)

The two IQ complex numbers are multiplied to extract phase for ranging.

How is remote_pct and local_pct measured and calculated?

[Elfving]

Hi,

My understanding is that the initiator is sending out channel sounding tones as well, which is measured on the reflector. Though this might not be immediately visible on the app side, it happens in the stack. I do not think it is really being synced with the initiator; its likely two measurements. Though I can double check if you want me to. 

Regards,

Elfving

[PaKa]

In the current Bluetooth spec the PCT data is sent from the reflector to the initiator as data payload. This consumes extra radio time compared to just the tone exhange. So basically item 1 from your question.

There is an upcoming optional spec change coming to Channel Sounding, Inline PCT, that will remove the requirement to transfer the data. This will speed up PBR but as it is optional, not all PBR based solutions can be expected to have this in place.

This is still not adopted in the Bluetooth SIG so you'll have to watch the releases from the SIG to see when it gets added.www.bluetooth.com/.../

[Ar K]

Thanks for the response. It makes sense. Could you point to which packet/structure from Initiator to Reflector contains this info. 
I found that within a device the HCI_LE_­CS_­Subevent_­Result contains the PCT.

But in which packet/structure is it sent to the other device/initiatior?

[Elfving]

Hi,

I hear this should be handled in the RAS files that are included. Have a look at <bluetooth/services/ras.h>.