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CC2640R2F: Conflicting AoA Results from Antenna Arrays

alig
Prodigy 190 points
Part Number: CC2640R2F
Dear Sir,
We have been experimenting TI board to calculate Angle of Arrival (AOA). Please see our results in the below table.
We used either A1 or A2 IQ data to calculate AOA no matter RSSI is high or low. In rows 2 and 3, the beacon is at A1 array side. A1 array gives good results. However A2 results are bad. 
In the lower 3 rows, the beacon is at A2 array side. A2 array IQ data gives good results. However A1 array results are bad.
The beacon in all experiments was approximately 120 cm away from the antenna. Our hypothesis is that both antenna arrays should give approximately the same quality results. We cannot figure out why the results are different for two antenna arrays. Any thoughts will be appreciated.
We eventually would like to use both antenna arrays and expect each one to give the right angles. 
Kind regards,
Ali
  • 0
    TI__Guru 57865 points
    Hi Ali,
    What SDK version did you use? What is your test environment (i.e. indoor/outdoor)?
  • 0 in reply to J Lindh
    Prodigy 190 points
    Hi Joakim,
    I used simplelink_cc2640r2_sdk_2_40_00_32 SDK. It was indoor but it was a big and totally empty place and antenna was far from the walls, I believe that's why I got very good results from antenna array which was at same side with beacon. But I couldn't get good results from antenna array which was at other side.

    Regards, Ali
  • 0 in reply to alig
    TI__Guru 57865 points
    Hi Ali G,
    Did you follow the required changes as mentioned in the AoA SLA; dev.ti.com/.../ble_aoa.html
  • 0 in reply to J Lindh
    Prodigy 190 points

    Hi Joakim,

    We followed those changes. However, we used antenna arrays separately to calculate AOA and compared them with each other.

    When  I looked at the link that you sent, I saw this picture: 

    According to this picture, antenna array 1 can cover approximately [0 1 2.. 135] degrees and so it cannot cover negative side. This matches with our results. Is this picture an accurate representation of the coverage of one antenna array? 
  • 0 in reply to alig
    TI__Guru 56215 points

    Hi,

    First off, when only using one array, you won't be able to tell whether the AoA packets comes from the front of the array of the back side of the array.

    When you say true angle =0, do you mean the middle point of the booster pack is angle 0?

    If that's the case, then when you place at 45 degree 1.2 meter away, what the array 2 sees might not be 45 degree at all... The angle that arrays 2 sees will vary based on the distance.

    For example, in the picture below shows that when you place beacon right in front of array 1, which if you use the arrow part of the booster pack, you will get a 45 degree as result.

    However, as you can see, it's not a 45 degree from array 2's point of view.

    If I misunderstand you, please provide a bit more information when you mean where the true angle is.

    Also how you calculate the angle.

    The only way to fairly compare the result from both arrays is to use A1.2 and A2.2 as 0 degree and compare result from there.