Before checking data rate you need to check whether there's enough signal power to start with.
Link budgets are the reasonable way to start, although in many more cases that one would bet on, the equipment is installed assuming that because the link is similar to other working links, everything is going to be ok, that hardly every is, but as long as enough signal power and BER low enough every one is going to be happy.
1.- This website
claims to be an Narrow Band IoT Link Calculator.
2.- These IEEE papers are related to your question
NB-IoT over Non-Terrestrial Networks: Link Budget Analysis
LTE IoT link budget and coverage performance in practical deployments
Do you have IEEE Explore access?
In one of these papers there's a preview table named 3pgg vs aligned link-budget assumptions, lots of assumptions.
3.- What are the link parameters you are working with?
4.- If you need a fast-forward speak to Harris
5.- IoT already 'piggy-backs' on other systems like 5G to be used on 'the last mile'.
I leave it to you to find out how it's encapsulated, but if 3GPP is already modulated to optical, reaching the outdoor unit up in the base station masts, to then go back to RF, sure the IoT can save the athmospheric loop by being inserted into already existing links : LEO preferably, but then Doppler and the choice of atennas may be an issue.
6.- From the Fraunhofer Institut for integrated circuits :
"..Thus an IoT terminal operating in a LEO or HEO network requires both a waveform tailored for the specifics of this communication channel and a suitable antenna design.."
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