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

[Simonr]

I'm sorry, I might have misunderstood your initial question. Are you asking why the I and Q are 90 degrees phase-shifted? If so, please check out section 2.4 in the whitepaper explaining the I and Q components.

Best regards,

Simon

[Saleh]

Thanks Simnor, but I think your first assumption was correct.

I know there is 90 degree phase-shift between I and Q samples, my question is why this phase-shift is not visible at the first 8 samples which corresponds to the "Reference Period" of CTE Signal.

Three first images of the main question, belongs to the samples generated by the Zephyr examples, and as you can see, "I" and "Q" have same phases at the first 8 samples in this images.

and

and this one

But fourth image is a third party implementation and you can see the phase-shift in this image.