NTN to TN Handover | 5G TN to NTN Handover

Introduction : Seamless handover between Non-Terrestrial Networks (NTN) and Terrestrial Networks (TN) is a critical component for enabling truly ubiquitous 5G/6G connectivity. In hybrid deployments, user equipment (UE) may transition from satellite coverage (e.g. LEO, MEO, GEO or HAPS) into terrestrial cellular coverage, or reverse, requiring sophisticated mobility management, conditional handovers (CHO) and service continuity strategies. This page explores NTN to TN handover and viceversa.

NTN to TN handover

It refers to situation where a user device is currently connected to satellite (NTN) and moves into coverage of terrestrial base station (TN) such as gNB. Following are use case trigger mechanism and generic process.

Use case: A user exits a rural/satellite only coverage area and enters city coverage with terrestrial 5G.

Trigger: Stronger/available terrestrial signal compared to the satellite link.

Key Process steps:

• The device monitors both NTN and TN signals.
• When TN coverage is better, the handover is initiated.
• The connection switches from satellite to ground based gNB.

Challenges: There is huge difference between propagation delay between ground to satellite (~250 to 500 ms) and ground to cellular tower (<10 ms).

TN to NTN handover

It refers to the situation where a device is currently connected to terrestrial (gNB) but moves out of its coverage area and must switch to the satellite (i.e. NTN). Following are use case trigger mechanism and generic process.

Use case: A user leaves urban/city coverage and enters remote/rural areas where only satellite NTN coverage is available.

Trigger: Terrestrial signal gets weak/lost, but NTN is available.

Key Process steps:

• Device monitors NTN beams (satellite coverage).
• Before terrestrial coverage is lost, a handover is prepared.
• The connection switches from ground network to satellite link.

Challenges: The major concern in this use case is beam management and Doppler shift occurred in satellite communication. Moreover, the UE must handle much longer round trip delays.

Conclusion:

In summary, enabling robust handover between Non-Terrestrial Networks (NTN) and Terrestrial Networks (TN) is foundational to achieving seamless, global connectivity.