For modeling the throughtput and/or packet collisions, it is important to understand which packets will show mutual interference at the receiver side. Here, two effects need to be considered: (a) interference immunity against signals on other frequencies, and (b) interference caused by LoRaWAN packets on the same frequency.
A report, analyzing aforesaid effects as well as the receiver sensitivity is available for download. Based on the measurement results, simple interference models can be setup to predict packet collisions in densely populated LoRaWAN networks: Final report (PDF)
A master/diploma thesis studying LoRa encoding/modulation and LoRa interference immunity can be download here: Interference Analysis of LoRaWAN Systems (PDF). This thesis has a very detailed explanation of the (officially undocumented) LoRa modulation/encoding scheme. The diploma thesis is accompanied by a Matlab library for generating LoRa-compliant baseband signals (LoRa_endoding_modulation (ZIP)).