Error in Angle of Arrival Calculation for Direction Finding

[Shivani]

Hello

We are using nRF5340 as our EVK with a 12 antenna array plate(4x4 with center 4 ones not being there). Our beacon uses nRF52833.

We used Nordic's sample codes- 'Direction Finding Central' to flash our EVK and 'Direction Finding Peripheral' to flash our beacon.

We tried using MUSIC algorithm on a python pipeline to obtain AOA.

However, when we tried to find AOA, we are not getting correct values. It is either completely random values or angle doesn't change at all. 

We get the IQ samples-

When plotted, we can see something like this:

What can we do about this?

[Edvin]

Hello,

It is either completely random values or angle doesn't change at all.

Did you change anything between these two observations? Because they are two very different cases. 

Please see the readme.rst file for the central_direction_finding sample:

* Guard period of 4 µs. There is a gap before the actual CTE reception and the adjacent PDU transmission to avoid interference.
* Reference period where a single antenna is used for sampling. The spacing between the samples is 1 µs and the period duration is 8 µs.
* Switch-sample period that is split into switch and sample slots. The length of each slot can be either 1 or 2 µs.

Can you try the nRF Connect for Desktop -> Direction Finding app (source is on github), using your HW, and we can see whether this works on your HW. This should help indicating whether this is a HW or SW issue.

BR,
Edvin

[Shivani]

Thankyou for the reply.

Can you please share the source for Direction Finding App since we are not able to find it on github?