Angle of Arrival (AoA) Calculation Producing Unexpected Values

[miladflores]

Hi,

I'm working on an indoor positioning system using an nRF5340 and a CHW1010-ANT1 antenna array. I'm receiving IQ samples from BLE CTE packets and using them to calculate the AoA. 

When I manually input IQ values, the AoA is correct and stable. However, when I use live IQ samples from the receiver, the AoA values fluctuate significantly, even though the transmitter and receiver are stationary.

As I understood it, the first 8 samples are from the reference period and should not be used to calculate the AoA and the first sample to be used (at index 8) is from antenna idx 1 and not 0 since 0 is used in the reference period. So the pattern goes 0 - 0 - 0 - 0 - 0- 0 - 0 - 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 0 - 1 - etc. Am I missing something here?

Below are some of the IQ samples I get.

Setup:

• Transmitter - nRF5340 sending BLE CTE signals
• Receiver - nRF5340 with CHW1010-ANT1 antenna array
• Antenna patches spacing - 5 cm
• UART - 115200 baud
• Antenna pattern - 0, 2, 4, 6, 8, 10, 12, 14

IQ sample values received:

Read from UART func:

Calculate AoA func:

Wavelength, Phase calc, and Phase wrap funcs:

I assume that the logic is correct since manually set values are showing the correct AoA.

Grateful for any help!

[Elfving]

Hi,

Are you using just one reciever? 

Our WP on DF typically clears up confusion regarding antenna switching patterns. Have you seen this?

As I understood it, the first 8 samples are from the reference period and should not be used to calculate the AoA

It should be used to calibrate.

So the pattern goes 0 - 0 - 0 - 0 - 0- 0 - 0 - 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 0 - 1 - etc. Am I missing something here?

Yeah, although that depends a bit on your pattern length, and whether these numbers refer to antennas, or order to antenna pattern etc.

What NCS version are you using? I guess all NCS versions should work, but we've only gotten the locator QDID (and therefore officially checked the locator) from NCS 2.2 with SDC, which I guess can be an argument for using that one. The zephyr controller also has a QDID for the locator that goes with NCS2.2.

Regards,

Elfving

[miladflores]

Elfving said:

It should be used to calibrate.

And would that be by getting the frequency offset from the reference samples and then using it to correct the remaining samples? If so, I'm thinking of something like this:

Elfving said:

Yeah, although that depends a bit on your pattern length, and whether these numbers refer to antennas, or order to antenna pattern etc.

In my cpunet.overlay I have set "dfe-antenna-num = <16>" since the antenna array consists of 8 antenna patches with polarization. Even numbers are horizontal and odd numbers are vertical.

Elfving said:

What NCS version are you using? I guess all NCS versions should work, but we've only gotten the locator QDID (and therefore officially checked the locator) from NCS 2.2 with SDC, which I guess can be an argument for using that one. The zephyr controller also has a QDID for the locator that goes with NCS2.2.

I'm running NCS 2.9.

Milad

[Elfving]

I guess we do not have that much in regards to materials on this, though this previous response by another customer might be worth a look.

Regards,

Elfving

[miladflores]

Thank you for your assistance Elfving!

Best regards,

Milad

[Elfving]

No problem at all Milad

Let us know if there is anything else!

Regards,
Elfving

[Louis Chen]

Hi Sir,

I have some questions and would like to ask you if it is convenient. I am currently using a similar configuration of NRF52833+Antenna (CHW1010-ANT1-1.0) as yours. How do I use your ANT RF SWITCH PIN9 (D0: Digital control input)?

Another question is, after setting the ANT pattern, I tried to connect to the CTE link AOA mode, but I found that my antenna array would not switch. I tried to measure from GPIO 3/4/28/29 but couldn't get it? Did you make any changes? I removed the ANT array and used the PCB antenna instead, but it didn't move at all.

[miladflores]

Hi Louis,

If I remember correctly I did not turn on that pin since it was used for AoD rather than AoA.

You should not be able to receive CTE on the PCB antenna only. 
Are you controlling what pins are set high/low on the nRF? Also, do you possess the complete datasheet provided by CoreHW?

FYI, I did switch antenna array from CHW1010-ANT1 to U-blox B10 antenna instead.

Best regards,
Milad