Handover lives or dies on the neighbour list
A dropped call in strong signal is almost always a missing or misconfigured neighbour relation. The neighbour list is the most under-maintained table in the RAN.
Every cell in a mobile network maintains a neighbour list — the set of nearby cells it expects a handset to move toward. When the user moves and the serving cell cannot find a target in its neighbour list, the handset either drops the call or attempts a slow, unreliable blind handover. Even with perfect RSRP, the call drops because the network does not know where to send it.
Neighbour lists grow stale as the network changes: new sites added, antennas retilted, frequencies refarmed, coverage patterns shifted by foliage or new buildings. In many networks, the neighbour list is generated once during site commissioning and never reviewed again. The result is a slow decay of handover performance that shows up in drive test statistics as 'unknown cause' dropped calls.
The maintenance discipline is straightforward: audit neighbour lists quarterly against actual handover attempts. Remove relations that never trigger — they waste resources in the system information broadcast. Add relations for cells that show frequent mobility between them. Use ANR (Automatic Neighbour Relation) where the vendor supports it, but validate the output: ANR is good at discovering new neighbours but has no incentive to prune stale entries.