LoraWan Chat and multicast with Subset-Difference-Method

We are proposed and developed the architecture and the basic components of an alternate comunication system in crisis situations.This system is useful when other comunication systems have crashed. Our proposals and architecture are use- ful generally in LoRaWan Networks that control devices with multicast transmitters. This work compares various wireless network technologies. Particular reference is made to the technology of LoRa and LoRaWAN, of which we will use. When analyz- ing and designing the system, we observed that the system is more efficient when using Multicast transmitters. The fast changes of system parameters and the neces- sity to send the same messages to different users each time, pushed us to research for a more efficient way.Thereafter we chose to use Broadcast Encryption method over LoRaWan network. The method we applied is the Subset Difference method. Thus we utilized LoRaWan Multicast transmitters on the network level and on the application level we used the Subset Diferrence method. Consequently,this makes it more flexible to select the number of users recieving messages. Conclusively, we developed a variety of applications that implemented our system.