Friday, January 1, 2016

Estimote vs Kontakt.io - Radiated Emission Measurements Comparison

In December, we took a thorough look at beacons in a semi-anechoric chamber. The chamber is equipped with a turn table, antenna for measurements and on the center of the table we placed a cardboard box to be used for mounting beacons in an upright position. This position is always depicted in showcase materials of beacon vendors, so we used it for a default setup. These were the positions the beacons were used in:


The overall setup of the measuring chamber was as follows. Beacons were in their initial position front-facing the measuring antenna. The measuring antenna was always in horizontal position. Beacons were transmitting with the power of +4 dBm.



We were interested in measuring of following factors: transmission channel (i.e. frequency), and radiated emissions in vertical and horizontal polarization. By Bluetooth LE specification. BLE device should use channels 37 (2402 MHz), 38 (2426 MHz), 39 (2480) for advertising. Advertising channels are allocated in different parts of the spectrum to provide immunity against interference from WiFi. 

Circular diagrams visualize field strength [dB(µV/m)] of radiated emissions in corresponding angle. Note that 180° is the initial position. Vertical polarization of the beacon is represented in orange, horizontal polarization is represented in blue.

Estimote beacon

The beacon without its cover reveals antenna located in the top part.





Kontakt.io beacon

Antenna of this beacon is the blue thingy next to the logo.




Conclusion

Both beacons were using all above-mentioned channels for broadcasting. Kontakt.io's transmission levels were stronger than Estiomote's.
When comparing field strength for vertical polarization, we can see that Estimote's field strength varies significantly along the measurement spectrum. The values for horizontal polarization are much more stable. Note that Kontakt.io's sudden drop around 90° and 270° is caused by side orientation of the beacon. Therefore it is desirable to place the beacons in production environments, to be facing the user if possible.
From the diagrams it is visible that calculation of distance based on FSPL is highly unreliable, since emitted signal strength varies not only from device to device, but also from beacon and measuring device polarization.
Any other thoughts?

Credits

Martin Pospíšilík - measurements
Adam Studenič - photos

8 comments:

  1. thank you for this work,:)

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  2. Kontakt.io does not put an antenna inside a board. The blue box near the top edge (between logo and beacon version) is an antenna.

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  3. Can you please elaborate more on the radar plot, especially in terms of what the blue and orange color stand for.

    Thanks in advance for your feedback & Great work!

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    Replies
    1. Orange plot visualises received signal strength radiated by the beacon placed in vertical polarisation. The blue plot visualises the same, but for horizontal polarisation.

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  4. How easy it is to replace battery in these kontakt beacons ?

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  5. And do u have comparison on how batter life compares between the 2

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  6. Great work, I'm using kontakt beacons for an outdoor solution an was analyzing the radiation pattern for the antennas and this looks really good. For the user who asked kontakt beacons battery is quite easy to replace. Keep up the good work!

    ReplyDelete