I have a task to build a wireless network consisting of devices (based on microcontrollers), which transmit data to the main unit.
The devices must be located in an open space on the field with ~2 km between each other, to record and process the data from the sensors and transmit the processed data to the main unit. The devices transmit data when some events take place(very rare) and the size of the data is about 50-150 bytes.
The network must have a mesh topology, so every device should also be a repeater.
So the question is, what technology and protocol are more appropriate for building this network with the specified spacing present between devices?