Why my IQ count is 1 ？ A confusion about direction finding which is connection based.

[Zihao]

Now I am using the https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_central/README.html and https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_peripheral/README.html  for a direction finding project.

I can run these samples successfully, but I have encountered an issue that confuses me.

I set the switch slot to 2 µs, allowing me to get a CTE with 45 IQ samples. However, the count of the IQ samples drops to 1 when the CRC is not OK. What does this single IQ data mean?

I only encounter this issue in the connection demos. In the connectionless demos, the count of the IQ samples is always 45, regardless of whether the CRC is OK or not.

This seems to indicate that a CTE with a wrong CRC can be used in connectionless demos but not in connection demos, for for greater accuracy in the connection mode, I guess.

Does this difference between connection demos and connectionless demos imply anything else? And why this difference exist?

This is really important to me. Thanks!

Request CTE from peer device...
success. CTE request enabled.
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -410
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -400
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -450
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -450
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -470
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -480
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -540
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -540
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -510
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -510
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -510
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -570
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -500
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -510
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -510
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -520
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -520
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 1, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC not OK, CTE Info OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490
CTE[E7:8C:85:B4:1C:E6 (random)]: samples count 45, cte type AOD 2 [us], slot durations: 2 [us], packet status CRC OK, RSSI -490

[JONATHAN LL]

Looking in to this and will update.

Regards,
Jonathan

[Zihao]

OK, thanks!

[JONATHAN LL]

Zihao said:

Hi, I'm using nRF52833 and ncs v2.2.0.

Was wondering if you where using our SoftDevice controller or the Zephyr BLE controller.

Zihao said:

and ncs v2.2.0.

Thanks

[Zihao]

OK. Since my task was mainly to get an Angle estimate, I hadn't paid much attention to this before. But I think I am using the Zephyr BLE controller. Because I find "find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})" in my CMakelist.txt.

[Zihao]

And I've noticed that the IQ count is not always just 1; sometimes it's 2 or 3. Currently, I'm utilizing the CTE data with 45 IQ samples to perform AoA and AoD estimation. But compared to the connectionless demo (where the IQ count is always 45), the efficiency is slightly lower.

[JONATHAN LL]

Zihao said:

But I think I am using the Zephyr BLE controller. Because I find "find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})" in my CMakelist.txt.

You need to check your .config file in the build folder, does it say CONFIG_BT_LL_SOFTDEVICE or CONFIG_BT_LL_SW_SPLIT ?

[Zihao]

OK, it said CONFIG_BT_LL_SW_SPLIT.