I am looking for a communication solution with the following requirements:
- unidirectional, point to point
- low power (li-ion battery powered, should operate at least one hour on the single charge)
- low baudrate data transfer (cca 40 - 80 bauds)
- long distance, in the terrain covered by the forest, behind the small hill. One km sholud be enough but more is better
- using free band within EU
What technologies should I check? Are there any existing modules for this? I would like to connect it to Arduino.