Questions Regarding NTN Integration, EPC Connectivity, and Channel Modeling in 5G-LENA

[Nikhil Gowda]

Dear 5g-Lena community developers and users,

I hope you are doing well.

I am currently working on an NTN-based simulation scenario using 5G-LENA(I am completely new to this ) where satellite nodes are propagating around Earth using an SGP4 mobility model. While implementing the setup, I encountered a few architectural and modeling questions for which I would greatly appreciate your guidance.

1. Connectivity of Non-gNB Nodes to EPC (SGW/PGW/MME) and IP Traffic Generation

From the documentation and examples available in 5G-LENA (NR module), it appears that all gNB nodes are directly connected to the EPC entities (SGW/PGW and MME).

My question is:

• Is it possible to connect a non-gNB node directly to the EPC (SGW/PGW/MME) and transmit IP traffic (e.g., UDP) through it?

• If yes, what would be the correct architectural approach to achieve this?

• Would this require creating a custom NetDevice or modifying the EPC helper configuration?

• Are there any example scripts or references that demonstrate such a configuration?

2. Dynamic UE Association in NTN Scenario (ConnectToGnb / ConnectToClosestGnb)

In my NTN scenario:

• Satellites (with and without gNB functionality) are moving dynamically using SGP4.

• Visibility and Line-of-Sight (LoS) between UE and gNB change during simulation time.

From what I observe, the ConnectToGnb() and ConnectToClosestGnb() methods seem to perform association at setup time rather than dynamically during simulation.

My concern is:

• In an NTN scenario, the UE should connect to a gNB only when it becomes visible (within LoS) during runtime, not statically before simulation starts.

• Is there built-in support for dynamic cell selection / re-association based on mobility and visibility?

• If not, what would be the recommended approach?

  • Trigger manual re-association events?

  • Extend the RRC layer?

  • Implement a custom handover/selection mechanism?

3. Channel Modeling Between gNB and UE (ThreeGppNtnChannel)

Regarding the PHY/channel layer:

• I would like to model the channel between gNB and UE using the ThreeGppNtnChannel model.

• Is it possible to directly use this model in place of the default terrestrial 3GPP channel model?

• If yes:

  • What modifications are required?

  • Does it require changes in the spectrum/channel helper configuration?

  • Are there specific attributes that must be enabled for NTN operation?

4. Can we override other antenna elements and does it support beam steering if we use other antenna patterns apart from UPA(isotropic antenna) ?

Additionally, if there are example configurations, papers, or implementation notes related to NTN channel usage in 5G-LENA, I would be grateful if you could share them.

To summarize, I am primarily looking for guidance on:

1. Direct EPC connectivity for non-gNB nodes and IP traffic routing.

2. Dynamic UE-gNB association in an NTN mobility scenario.

3. Proper integration and configuration of the ThreeGppNtnChannel model.

Any pointers, references, or architectural suggestions would be extremely helpful for progressing with this work.

Thank you very much for your time and support.

Kind regards,

Nikhil GS