Handover (also called handoff) is the technology that automatically switches the connected base station as a mobile phone user moves. It maintains seamless connectivity during calls and data sessions without interruption. Without this technology, calls would disconnect every time a user crossed a cell boundary.
There are multiple types of handover. Soft handover maintains connections to both old and new base stations simultaneously during the switch, used in 3G (CDMA). Hard handover disconnects from the old station before connecting to the new one, and is the primary method in LTE and 5G. The switch completes in tens of milliseconds, so call interruption is rarely noticeable. In high-speed environments like bullet trains, base station placement along the route is especially critical as handovers occur very frequently.
In high-speed environments like bullet trains (over 300 km/h), base stations switch every few seconds, resulting in very high handover frequency. Each carrier installs dedicated base stations along bullet train routes with directional antennas aligned to the direction of travel, ensuring call quality during high-speed movement.
Switching between different radio technologies (e.g., moving from a 5G area to a 4G area) is called inter-RAT handover and is technically more challenging. With 5G coverage still limited, this type of handover occurs frequently, and each carrier is working to improve quality. Handover quality directly affects call drops and audio distortion, so when choosing a carrier, consider not just coverage maps but also real-world call quality during movement.