RSSI Kalman Filtering:

From philipiv
https://github.com/philipiv/rssi-filtering-kalman

Xbee trilateration project:

Units of the coordinates are in meters
Place xbee Reciever A at coordinates (0,0)
Place xbee Reciever B at coordinates (0,3)
Place xbee Reciever C at coordinates (4,3)
Run Demo1/main.py code on Transmitter xbee being tracked
Use LocationTracking.py to graph the trilateration results

In xctu:

Update radio module firmware with: Digi XBee3 Zigbee 3.0 version 100B
Load default settings
Transmitter CE (Device Role) Form Network [1]
Receivers CE (Device Role) Join Network [0]
Set receivers with AP: API Mode Enabled [1]
Set receiver and transmitter devices with ID: 2018
Set receiver and transmitter devices with NT: 32
Set 1st receiver NI : RECEIVER_A
Set 2nd receiver NI : RECEIVER_B
Set 3rd receiver NI : RECEIVER_C

Hardware set up:

Ensure jumper is on loopback (as is out of box)
Connect antennas on receivers and transmitter
Connect transmitter xbee to pc via usb
Connect to COM port of transmitter and run code

Links to research articles used:

Research on ZigBee Indoor Technology Positioning Based on RSSI
Zhou Yang Dong, Wei Ming Xu, Hao Zhuang:
https://www.sciencedirect.com/science/article/pii/S1877050919308294?fbclid=IwAR33niwCr5z439DuppIMkdGoEq7f7sivn9wlmPUm_trzS4d1zXRhzjMPNa8
Predict distance(m) of an object based on its RSSI(dBm)
RSSI = A + N * ln(distance)
RSSI = -33.874 - 17.27ln(distance)
Your A and N values will vary!
A = -24.514
N = -15.41
distance = e ^ ((rssi-A)/N)

Node Positioning in ZigBee Network Using Trilateration Method Based on the Received Signal Strength Indicator (RSSI)
R. Mardeni, Shaifull Othman:
https://www.researchgate.net/publication/265937701_Node_Positioning_in_ZigBee_Network_Using_Trilateration_Method_Based_on_the_Received_Signal_Strength_Indicator_RSSI