Bugzilla – Bug 2001
Cost231PropagationLossModel is imprecise
Last modified: 2017-12-03 07:24:52 EST
The model is "wrong" in two main points:
1) the speed of light is 299792458 m/s, not 300000000 m/s.
2) the last term in the equation is set to 10 dB, whereas the model states that it should be either 0 or 3 dB (depending on the environment).
Fixing the two may change (slightly) the simulation results. Even not so slightly, since there will be a 7dB difference (at best).
sorry, I didn't realize the speed of light discussion was here also; opened a separate bug 2011 for the constant value.
Let's keep this bug scoped to the Cost231 model, and make the fix of lambda depend on the bug 2011.
Created attachment 2613 [details]
Here is a proposed patch addressing the two issues mentioned by Tommaso. I did not test it.
As Tommaso mentioned, the change affects the behavior of the model for all distances, with a non negligible impact in simulation results for typical scenarios.
I am not sure how much this COST 231 model implementation is used, I just recall that LTE simulation typically use OkumuraHataPropagationLossModel, which is in fact an alternative implementation of this model. I've seen just a few examples in the code base that use this model. This considered, how do you feel about pushing this patch?
Created attachment 2718 [details]
Fixed default value for Lambda attribute so it corresponds to default Frequency.
There's an additional point, raised in the ns-3 users' group:
The COST 231 model is meant to be used in 1.5-2.0 GHz range, while the default frequency in the model is 2.3 GHz.
We should (at least) give a warning when one uses the model outside the normal range and (definitely) not use a default value of 2.3 GHz.