nRF51822 beacon kit: big notches in RSSI vs distance plot

[classicman]

Hello everybody,

I'm designing an app to track the position of the smartphone using six beacons and, in order to do that, I made some measures both indoors and outdoors and plotted a graph of RSSI vs distance using the data acquired from nRF Connect app (exported to .csv and fed to Matlab). The first set of measures was taken in a corridor about 3m wide and 35m long at different transmission power level, the second set was taken outdoors in an open field about 30x25 m at 0 dBm transmission power. Both the plots show serious notches, as you can see from the pictures, causing great troubles with the accuracy of the tracking.

I'd like to know if this behaviour is to be expected or there is something wrong in the setup of the measures.

Thanks.

[classicman]

Thank you both for your replies.

While the data is not raw since the nRF Connect app itself plots the average value of the RSSI over different packets received, I do agree that more sophisticated filtering along with additional information might be of great help to calculate the position of the smartphone.

I guess I still need to figure out how to proceed.

But first, since I was asked for a notch-free plot, I'd like to remove those. Do you think the graph could benefit from taking measures in an open field (like, an actual field, completely free of obstacles in every direction) or the reflections of the ground will always be a problem, and I should focus my efforts towards the filtering only?

Thank you all again.

[classicman]

Thank you all for your insight (and useful links).

The app would not be sold, it's just a University project, so at least that is not an issue.

Yes, I do have more than one beacon available, in fact I was planning to use six for a single room.

May I ask @RogerClark, what problems did you meet when trying to interface with accelorometers? Because that's something my professor mentioned, using accelerometers in aid of the RSSI.

Thanks.