Communication Protocol and device selection for long range communication.

Hello!

I currently work on a project that requires a long range communication about 15 to 20 km away. I will use arduinos uno to accomplish this project.

What i would like to know is which communication protocol should i use except GSM module, for economic reasons.

I want to establish communication between 3 arduino uno.

Someone suggested me to work with rfm95 which has lora modulation and a long range coverage but i dont know if this can work with more than 2 arduinos.

I would be really gratefull if you could help me with this!

GSM is the only simple method to do this.
The distances you require are too far for any simple radio based solution.
However,if the locations of the end points are all line of sight to each other then it may be possible to use a radio based solution.
Far more information is needed.

All equipment operating in the ISM bands is low power and therefore short range.
Long range communication will require equipment that uses a licensed band which costs money.

as mentioned by mauried, if you have line of site, you may be able to work with some point to point solutions. i would look at 900mhz analog gear (used for scada), or some of the 900mhz ip gear (ubiquity as an example), but its going to be directional antennas all around.

given what it costs though to put up a pole and buy the hardware though, GSM is probably your most economic solution. i was recently involved in some scada upgrades, and a 50' pole was running around $10,000usd installed. it doesn't take much of a hill or road to negate that height of tower though, and in my area, 50' is the limit before you need to meet navigation requirements.

Obvious question...could you access wifi at each location?

scrumfled:
Obvious question...could you access wifi at each location?

Hello,

Unfortunatelly, No i don't. This is why i am looking towards lorawan.