Direction finding on NRF52811

RE: Direction finding on NRF52811

Simonr — Fri, 22 Oct 2021 08:17:33 GMT

Hi Sergey

Okay, so support for the nRF52811 in the direction finding sample is still upstream in the Zephyr project, and has not yet been added in the nRFConnect SDK (NCS). It will likely be added in the next release of NCS. The upstream version is available here, where the nRF52811 board .dtsi and kconfig files to add Direction Finding support.

Best regards,

Simon

RE: Direction finding on NRF52811

Sergey_Ladanov — Fri, 22 Oct 2021 07:02:36 GMT

Okay. I will wait a responce. Thank you!

RE: Direction finding on NRF52811

Simonr — Fri, 22 Oct 2021 05:19:59 GMT

I've been able to reproduce this on my side with an nRF52811 as well. And it seems like the nRF52811 is not supported by default as a AoA TX device. I've asked the development team what needs to be done and will get back to you when I hear from them. As of yet I don't have any idea what exactly is causing it to fail.

Best regards,

Simon

RE: Direction finding on NRF52811

Sergey_Ladanov — Wed, 20 Oct 2021 13:13:33 GMT

Hi Simon

These are settings of the adv_set structure:

And these are settings of the cte_params structure:

I have not changed the main.c file from this example

RE: Direction finding on NRF52811

Simonr — Wed, 20 Oct 2021 11:31:06 GMT

Hi Sergey

Error 134 points to an unsupported value being input into a function, so it seems you have added a value that's not supported in your bt_df_set_adv_cte_tx_param() function. What is adv_set and cte_params set as in your application?

Best regards,

Simon

RE: Direction finding on NRF52811

Sergey_Ladanov — Tue, 19 Oct 2021 17:56:35 GMT

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334910#334910"]What board file did you add for the nRF52811 when trying to build it, and did the compilation and build process return successfully or did you see any error codes?[/quote]

I added the ubx_bmd360eval_nrf52811 board for building the project:

The content of the prj.conf file:

Compilation was with no errors:

I started debugging, the application get error in function bt_df_set_adv_cte_tx_param (error code is -134):

RE: Direction finding on NRF52811

Simonr — Tue, 19 Oct 2021 13:30:47 GMT

Okay, I think it's safe to say it's not due to the testing environment at least. Indeed, testing with one antenna should give you rather stationary values here.

What board file did you add for the nRF52811 when trying to build it, and did the compilation and build process return successfully or did you see any error codes?

Best regards,

Simon

RE: Direction finding on NRF52811

Sergey_Ladanov — Tue, 19 Oct 2021 12:02:10 GMT

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334732#334732"]

Some formulas calculating with I/Q Signals translating between polar and rectangular form etc.

Peak Amplitude A = (I²+Q²)½

Phase Angle ϕ = tan⁻¹(Q/I)

I = A⋅cos(ϕ)

Q = A⋅sin(ϕ)

Converting IQ Data to a plain signal: I is the original signal.

Euler form: A⋅eiϕ = A⋅(cos(ϕ) + i⋅sin(ϕ)) = I + Qi

[/quote]

I calculated phase angles and peak amplitudes by iq samples and got the following results:

As an experiment I have tried to receive iq samples on one antenna (the beacon and locator were stationary), the results look like this:

But it seems to me that the phase should be approximately the same under such conditions. Am I right?

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334732#334732"]Can you provide some details on the environment though?[/quote]

I tested the devices in a private house outside the city so that there are no other signals.

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334732#334732"]How exactly does the transmitter "not work"? Are you able to build and run the application, and are then running into some issues or are you having issues flashing the application onto your custom board?[/quote]

I built a transmitter example application and loaded file zephyr.hex (from /build/zephyr folder of project directory) into the NRF52811 chip. Then I tried to see some data from the transmitter using BLE Sniffer (based on NRF52840-DONGLE board), but there was nothing.

Source files of this example:

devzone.nordicsemi.com/.../AoA_5F00_Beacon.zip

RE: Direction finding on NRF52811

Simonr — Tue, 19 Oct 2021 06:52:27 GMT

Sorry, I also forgot to mention the most likely reason you're seeing "random" values.

Are you handling these values at all after you receive them? Raw IQ data won't make any sense by itself, as you always need to convert them to a vector. Then you can assess the vector after that. This is explained quite well here. Please check out the following formulas specifically:

Some formulas calculating with I/Q Signals translating between polar and rectangular form etc.

Peak Amplitude A = (I²+Q²)½

Phase Angle ϕ = tan⁻¹(Q/I)

I = A⋅cos(ϕ)

Q = A⋅sin(ϕ)

Converting IQ Data to a plain signal: I is the original signal.

Euler form: A⋅eiϕ = A⋅(cos(ϕ) + i⋅sin(ϕ)) = I + Qi

Best regards,

Simon

The antenna switching and IQ packet transmissions need to match in time. It seems you've done that correctly. I'm guessing the custom board is fine as you seem to be aware that the custom board lacks the external LF clock and have configured it for that. Can you provide some details on the environment though? Depending on the locator board, there will be a different "sweet spot" for it where it receives the most accurate values. I don't know what this is for your locator board, but I'd recommend trying to move the beacon so that it is at different angles from the locator.

How exactly does the transmitter "not work"? Are you able to build and run the application, and are then running into some issues or are you having issues flashing the application onto your custom board?

Best regards,

Simon

RE: Direction finding on NRF52811

Sergey_Ladanov — Mon, 18 Oct 2021 13:41:03 GMT

Thank you for reply!

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334516#334516"]Are you sure that the antenna switching and time between each IQ packet matches, so that it's getting picked up correctly.[/quote]

How can i check it correctly?

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334516#334516"]What kind of device is the advertising device, is it an nRF52833 DK for instance or a cusotm board?[/quote]

It is a custom board on NRF52811.

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334516#334516"]In what kind of environment are you testing this application? If you're in an office environment with a lot of BLE devices you might have some interference issues. Also, how are the boards positioned compared to one another?[/quote]

The IQ samples given here were received with only one BLE device.

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334516#334516"]Also, how are the boards positioned compared to one another?[/quote]

The boards were positioned as follows:

[quote userid="75734" url="~/f/nordic-q-a/80726/direction-finding-on-nrf52811/334516#334516"]I would suggest checking out the direction finding example projects in the nRFConnect SDK for reference. Locator can be found here, and transmitter here.[/quote]

Can I run this examples on NRF52811? I have tried to run the transmitter example by selecting ubx_bmd360eval_nrf52811 board and by using "CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y" option, but it did not work

RE: Direction finding on NRF52811

Simonr — Mon, 18 Oct 2021 08:55:03 GMT

I didn't spot anything looking at your code snippets, but there are a few things to look out for. First off, using only 4 antennas are not great to get very accurate data, but I agree that it should yield better results than what you get here. Are you sure that the antenna switching and time between each IQ packet matches, so that it's getting picked up correctly. What kind of device is the advertising device, is it an nRF52833 DK for instance or a cusotm board?

In what kind of environment are you testing this application? If you're in an office environment with a lot of BLE devices you might have some interference issues. Also, how are the boards positioned compared to one another?

I would suggest checking out the direction finding example projects in the nRFConnect SDK for reference. Locator can be found here, and transmitter here.

Best regards,

Simon