Bluetooth trilateration using nRF5340

[Theodorul]

Hello, I am a total beginner in working with RTOS and Zephyr and nRF devices. I would like to build a Wireless Sensor Network which consists of 3 nodes (maybe set in a Bluetooth Mesh) whose primary objective is to measure the RSSI values from each of them to a moving beacon and transmit the values to a computer running MATLAB. The computer running the MATLAB program should, then, indicate the position (in x and y coordinates) on a real-time updated map of the moving beacon. 

I have successfully flashed the "nrf_dm" example on two boards and have visualised the RSSI value of one in respect to the other in the VSCode Terminal (just to analyse the different values of it). Also, I have flashed the "peripheral_hr" example on another board and have successfully plotted the value of the "heartrate" in a real-time updated figure in MATLAB (to demonstrate the successful connection between a nRF5340 and my laptop).

So I have several questions:

1. Is this possible?

If yes,

2. Which examples can I further look into in order to achieve this? 

The application is destined for indoor asset tracking and even though the accuracy of RSSI trilateration is around 1m I will be trying to improve it by Kalman Filtering in MATLAB.

[Simonr]

Hi Theodor

Yes, this is possible, but maybe the Direction Finding feature in BLE might be more like what you're looking for. We have some samples for a connectionless locator and beacon where you should also be able to add I.E. the heart rate service to the beacon so that the locators can first locate the device and afterwards pick up on the heart rate of said beacon (or vise versa). Note that you will also need 2 or 3 locators here as well to get it down to being very accurate, but with this it should be possible to get down to single cm accuracy. 

Connectionless beacon: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_connectionless_tx/README.html

Connectionless locator: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/bluetooth/direction_finding_connectionless_rx/README.html 

If not, the nRF DM sample will likely work as well, but we don't have any samples where centrals triangulate the position of one device with this setup. You will have to do the calculations on your own.

Best regards,

Simon