NS_ASSERT failed: BuildingsChannelConditionModel only works with MobilityBuildingInfo — How to Fix?

[Antonio Sergio de Sousa Vieira]

Hello everyone,

I'm working on a V2X/V2I simulation in NS-3 using the 5G LENA module. My scenario involves vehicle and GNb mobility traces (NS2 format), building modeling, and 5G NR sidelink/groupcast communication. The main script is [`cttc-nr-v2x-mec.cc`](https://github.com/sergiosvieira/v2i_v2x_5glena).

When I run the simulation, I encounter the following error:

```
NS_ASSERT failed, cond="a1 && b1", msg="BuildingsChannelConditionModel only works with MobilityBuildingInfo", +0.000000000s 0 file=/home/sergiosvieira/ns3-5glenna-v2x-v2i/ns-3-dev/src/buildings/model/buildings-channel-condition-model.cc, line=62
```

I've reviewed my code to ensure I'm calling `BuildingsHelper::Install(ue_nodes);`, and my mobility traces and GNb positions are loaded as described in the README. The full source is public here: [https://github.com/sergiosvieira/v2i_v2x_5glena](https://github.com/sergiosvieira/v2i_v2x_5glena).

**My questions:**
- What does this assertion mean in practice?
- Is there something I need to change in how I install mobility/building info, or in my NS2 trace files, to ensure `MobilityBuildingInfo` is present on the nodes?
- Is this related to the order of installation of mobility/building info, or to the type of mobility model used?
- Are there recommended practices or minimal working examples for integrating buildings and mobility with 5G LENA V2X?

**Additional context:**
- NS-3 version: 3.42
- 5G LENA V2X: v2x-lte-dev
- OS: Fedora 42

Any help, insights, or pointers to documentation/examples would be greatly appreciated!

Thank you in advance,

Sérgio Vieira  
Federal Institute of Education, Science and Technology of Ceará  
sergio...@ifce.edu.br

[Gabriel Ferreira]

- What does this assertion mean in practice?

BuildingsChannelConditionModel requires both devices in a channel have the MobilityBuildingInfo.
That asserts tells us that you didn't install MobilityBuildingInfo to all devices using the helper.
Which is true, because you forgot to include gNBs.

If you debug, that is what you are going to see, a gNB talking to an UE.