NTN Handover
Also known as: Non-Terrestrial Network Handover
Definition
The 3GPP-defined procedure for transferring an active radio connection between non-terrestrial coverage beams, satellites, or feeder links, incorporating satellite ephemeris and predicted timing/Doppler trajectories to trigger handover ahead of signal degradation rather than reactively.
Key Points
- Extends 3GPP handover procedures (measurement, decision, execution) with satellite ephemeris data so the network and device can predict handover timing rather than relying solely on real-time signal measurement
- LEO NTN handover is far more frequent than terrestrial cellular handover — a fast-moving satellite's beam footprint sweeps across a fixed ground point in minutes, not the hours a terrestrial cell boundary might go unchanged
- Two distinct handover types apply: service-link handover (UE moves between satellite beams or between satellites) and feeder-link handover (gateway switches from one satellite to the next as it passes overhead)
- Earth-fixed beam architectures reduce service-link handover frequency by steering beams to track a ground footprint, trading onboard beam-steering complexity for fewer handover events
- Handover failure during a satellite pass causes a service interruption that, unlike a terrestrial dropped call, cannot simply reconnect to the same cell moments later — the satellite has physically moved on
Concept
Because a LEO satellite's position relative to any ground point is known in advance from its orbital ephemeris, the network can schedule an NTN handover proactively rather than waiting for signal quality to degrade as it would with a terrestrial cell edge. The UE and network exchange predicted timing advance and Doppler values for the upcoming satellite before the handover executes, allowing the connection to re-synchronize quickly once it switches. Feeder-link handover operates on a separate, longer timescale — a gateway typically hands off to the next satellite in the constellation as the current one passes below its horizon, independent of any individual user's service-link handover.
Explainer
The operational failure mode unique to NTN handover is that a missed or late handover cannot be recovered the way a terrestrial dropped call can, because the satellite's geometry has moved on by the time a retry would occur — there is no "same cell, try again" fallback. This makes handover timing prediction accuracy, not just signal strength measurement, a hard requirement: if the UE's ephemeris-based timing prediction drifts from actual satellite position, the handover executes against a link budget that no longer matches reality. Earth-fixed beam satellites mitigate handover frequency by continuously repointing their beams to hold a stable ground footprint, at the cost of onboard beam-steering complexity and power budget; satellites without earth-fixed beams instead hand users between beams every few minutes as the satellite's fixed-beam footprint sweeps past, producing a much higher handover rate that stresses network signaling capacity at scale. For CE verticals, this distinction matters directly: a maritime vessel on a long ocean crossing or an aircraft on a transoceanic route will experience dozens of NTN handovers per hour under a non-earth-fixed-beam constellation, making handover success rate — not just raw link budget — a primary driver of perceived service continuity for those use cases.