Bug 2001

Summary:	Cost231PropagationLossModel is imprecise
Product:	ns-3	Reporter:	Tommaso Pecorella <tommaso.pecorella>
Component:	propagation	Assignee:	Nicola Baldo <nicola>
Status:	PATCH PENDING ---
Severity:	enhancement	CC:	krotov, ns-bugs, tomh
Priority:	P5
Version:	ns-3-dev
Hardware:	All
OS:	All
Bug Depends on:	2011
Bug Blocks:
Attachments:	proposed patch Proposed patch

Description Tommaso Pecorella 2014-10-03 16:27:55 UTC

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).

Comment 1 Tom Henderson 2014-10-20 09:39:46 UTC

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.

Comment 2 Nicola Baldo 2016-10-12 18:04:52 UTC

Created attachment 2613 [details]
proposed patch

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?

Comment 3 Alexander Krotov 2016-12-28 12:03:58 UTC

Created attachment 2718 [details]
Proposed patch

Fixed default value for Lambda attribute so it corresponds to default Frequency.

Comment 4 Tommaso Pecorella 2017-12-03 07:24:52 UTC

There's an additional point, raised in the ns-3 users' group:
https://groups.google.com/forum/#!topic/ns-3-users/cQpBK9XbpGc

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.