If you want to work with LoRaWAN in particular, LoraSim and FREE are good options. If you intend to work extensively with PHY / MAC layer, NS-3 has two separate modules for that - (i) ns-3 module PHY focus and (ii) ns-3 module MAC focus. On a different note, if you want something simple, SimpleSoft might help. However, this research paper will surely give you some insights regarding LoRa/LoRaWAN simulator ( 10.1109/IMITEC45504.2019.9015882).