A base station is wireless equipment that connects mobile phones and smartphones to a carrier's network via radio waves. Consisting of antennas, transceivers, and control units, base stations are installed on building rooftops, towers, and utility poles. Mobile calls and data sessions reach the network through a base station.
The area covered by a single base station is called a "cell." Cell size varies greatly by environment - a few hundred meters in urban areas, several kilometers in suburbs, and potentially tens of kilometers in mountainous regions. Urban cells are small because the high density of users requires distributing the load across more stations. Covering an area with these cells is the origin of the "cellular" name, and why mobile phones are called "cellular phones" in English.
As users move, the connected base station switches automatically (handover). The switch takes only a short time, so calls are unlikely to be noticeably interrupted even during movement.
With the spread of 5G, deployment of millimeter-wave small cells is advancing in urban areas. Millimeter wave enables high-speed communication but has short range, requiring densely deployed small base stations - installation on streetlights, traffic signals, and similar structures is being explored. Securing installation sites and addressing aesthetic concerns are ongoing challenges requiring coordination with local governments. Carriers compete to expand coverage. Each carrier's official website provides coverage maps for checking signal conditions at home and work.