AoA Collected IQ data not stable for a stationary scenario

[Miguel Roque]

Hello all,

I'm currently working on an evaluation of a AoA location system. For that I'm making use of the Nordivc 12 Array Antenna, and two nRF52833 DK (one connected to array antenna and the other is being used as object to be located). Regarding the firmware, I'm using the Zephyr nRF Connect examples (direction_finding_central and direction_finding_peripheral). I'm sampling the IQ data from array antenna and processing it with a python algorithm on my PC.

System configuration:

• CTE period: 160us
• Sample slot period: 2us
• IQ samples captured: 45
• Antenna pattern used: 2 antennas [ANT_11 ANT_12] (ANT_11 is PDU also)

The problem at this moment, is that in a static scenario (both array antenna and object to be located are static), the sampled angle is not stable and always jumping in a "aggressive" way. I know that is really probable that the problem is in my "angle script", but at this moment I want to validate if the data that I'm gathering is reliable and valid. How can I do it? Sample the IQ data and convert it to amplitude and angle and analyse it?

Thank you by your time in advance!!

Miguel Roque

[PaKa]

sample data and convert to amplitude and angle and then evaluate the stability of the angle is the way to go. Remember that the none of the frequencies in the system are fixed so you need to calculate the frequency of the reference signal based on the phase change over time. If you input 250KHz or 500KHz into your script then it is already guaranteed to fail hard.

[Miguel Roque]

So your suggestion is to sample the IQ data from the two near antennas, convert it to amplitude and angle and then try to figure it out if the phase difference remains stable (considering a static scenario)?

[PaKa]

First check that you can verify that your phase calculations work correctly with a single antenna, then check with multiple antennas in a static environment before testing things in a dynamic environment. Easier to debug when you have few changing parameters.