Also known as: handover, handoff, cellular handover
Handover (also handoff) is the process by which a cellular network transfers an active call or data session from one cell to another as the user moves, so that the connection continues without being dropped.1 It is the mechanism that makes mobility work: a moving handset is continually handed between base stations, ideally without the user noticing.
How it works
The handset continuously measures the signal quality of its serving cell and of neighbouring cells it can hear. When a neighbour becomes sufficiently stronger — subject to a hysteresis margin and timer that prevent rapid ping-ponging — the network commands a handover. Two broad styles exist:
- Hard handover (break-before-make): the old link is released before the new one is established, so the device is momentarily connected to exactly one cell. This is the norm for GSM and LTE, where cells use different frequencies or the transition is fast enough to be seamless. LTE handovers are often coordinated directly between base stations over the X2 interface.
- Soft handover (make-before-break): the device connects to both cells at once and releases the old one only after the new one is solid. This is characteristic of CDMA systems, where all cells share one frequency so a phone can combine signals from several simultaneously; a special case within one base station’s own sectors is called softer handover.
When there is no active session, the equivalent idle-mode process is cell reselection: the camped-on handset simply re-picks the best cell using slower, more power-efficient measurements, without any signalling handover.
Relevance to SDR
Handover is a cellular-network procedure, and the signalling that carries it is part of the licensed, and on modern networks encrypted, control plane — not something a scanner tunes directly. It is relevant to the SDR world because the same core problem appears in the trunked land-mobile systems GopherTrunk does decode: as a user drives across a wide-area network, the radio must move between neighbor sites in a multisite trunking system, and the control channel announces those site transitions. Following that mobility — tracking a talkgroup as it roams across sites — is squarely in GopherTrunk’s wheelhouse, even though cellular handover itself is out of scope for its air interfaces. The idea is also distinct from roaming, which is switching between operators rather than cells.