NTN-CHO Framework

TTE-Aware 3GPP Release-17 Conditional Handover for 6G LEO Satellite Networks

---

Why this module

LEO satellite handover is fundamentally an orbital-dynamics problem: a candidate cell that satisfies the 3GPP Release-17 conditional-handover (CHO) trigger at preparation can leave the user horizon before execution completes. This module integrates an orbit-informed Time-to-Exit (TTE) estimator into the standard Rel-17 CHO state machine, eliminating ping-pong handovers (57 % → 0 %) and reducing total HOs by 3.4× without breaking compliance with the existing RRC message set.

At a glance

Metric (10-seed × 600-s, 66-sat Walker-Star)	TTE-aware (this work)	Location-only	A3 event
Handovers / seed	135 ± 12	200 ± 40	463 ± 48
Ping-pong rate	0.0 %	57.1 %	50.2 %
Success rate	83.1 ± 4.6 %	98.7 ± 0.5 %	70.3 %
TTE prediction cost	O(log n) per candidate	n/a	n/a
Statistical test (Wilcoxon vs A3)	p < 0.005	—	—

What it does

• 3GPP Rel-17 CHO state machine (PREPARE → MONITOR → EXEC) with the standard four trigger types (A3 / D1 / time-based / event-based) plus a novel TTE trigger
• TTE estimator using SGP4 ephemerides + TR 38.811 antenna patterns, coarse-forward + binary search in O(log n)
• Analytic error bound: σ_τ ≈ σ_AT / v_gs, validated against measured along-track residuals from contemporary IEEE TAES literature
• Per-class realistic UE mobility helper covering all 7 TR 38.811 §6.1.1.1 classes (handheld / pedestrian / vehicular / HST / maritime / aviation / IoT)
• Native ns3-ai bridge: 68-feature observation vector exposed via Gymnasium 1.0
• ntn-cho-full-constellation reference example and 10-seed Monte-Carlo build pipeline

Live demos

Per-UE handover behaviour over a 600-s LEO pass

Four-algorithm comparison (TTE-aware vs. Location vs. A3 vs. Time)

Install & run

See INSTALL.md for the full step-by-step guide (ns-3.43, SNS3 satellite module, build flags).

Quick taste:

git clone https://github.com/Muhammaduazir69/ntn-cho-framework.git contrib/ntn-cho
./ns3 configure --enable-examples --enable-tests
./ns3 build
./ns3 run "ntn-cho-full-constellation --algorithm=tte-aware --simTime=600 --rngRun=1"

Documentation

• INSTALL.md — detailed setup + dependency notes
• docs/architecture.png — module architecture
• Reference paper: Time-to-Exit Conditional Handover for 6G LEO Satellite Networks, IEEE TAES, in submission

Cite this work

@misc{uzair2026ntncho,
  author = {Uzair, Muhammad},
  title  = {NTN-CHO Framework: TTE-Aware Conditional Handover for 6G LEO Satellite Networks},
  year   = {2026},
  url    = {https://github.com/Muhammaduazir69/ntn-cho-framework}
}

Part of the ns3-ntn-toolkit

This module is one of five custom modules bundled in ns3-ntn-toolkit — a pre-integrated ns-3.43 distribution for 6G NTN research:

Module	Repo
Toolkit (umbrella)	ns3-ntn-toolkit
ntn-cho	this repo
oran-ntn	oran-ntn
thz-ntn	ns3-thz-ntn
ns3-ai (fork)	ns3-ai

License

GPL-2.0-only — see LICENSE.

Acknowledgements

ns-3 core team · SNS3 maintainers · 3GPP RAN2 Rel-17 specifications.