Problem with I and Q Samples During the Reference Period of CTE Packets

[Saleh]

Hi

As described in this white paper: https://infocenter.nordicsemi.com/pdf/nwp_036.pdf during the reference period of CTE signals, 8 samples are taken. These samples contain both "I" and "Q" elements of signal which has different phases relatively.

I have captured the reported "I" and "Q" samples using the samples provided by SDK:

• https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_connectionless_tx/README.html
• https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_connectionless_rx/README.html

For the reference period, I can not see any phase difference between "I" and "Q" elements (while it should be different). I have visualized the data and you can see the result in the below images:

IQ samples with 2us switching slots and using PCB antenna:

IQ samples with 1us switching slots and using PCB antenna:

IQ samples with 1us switching slots and using array antenna:

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As you can see, in all conditions, the reference period has the similar behavior. I have plotted a third party product which uses the CTE packets and you can see the visualized data here,

Obviously the "I" and "Q" samples are in different phases during the reference period. What is wrong in the above nRF examples?

Regards,

Saleh

[Saleh]

Thank you for clarification, It helped too much.

To prevent any misunderstanding specially for beginners, I suggest to change the default physical bit rate of the "tx sample", from 2MB to 1MB, by adding the "BT_LE_ADV_OPT_NO_2M" parameter option.

Also as you can find in this document: https://www.bluetooth.com/bluetooth-resources/bluetooth-direction-finding/

Page 26, part "5.3 Choices of PHY", has declared that support of 1MB is mandatory and 2Mb is optional. so from this point of view, choosing the 1MB as the default bit-rate could be a better option.

[Piotr]

Thank you for the suggestion, we will consider possibility to go with 1M PHY.

[AllenWang]

Hello, Saleh:

    have you got this question resolved. I met the same issue as you. hope get kindly guidance from you

   

thanks and best wishes

[Simonr]

Hi Allen

I see you have created a ticket of your own here. I'll reply to you there, as this ticket is ~2 years old at this point.