Mobile radio waves
携帯電話の電波 keitai denwa no denpa
The wireless signal between a phone and a base station. Coverage, frequency, building materials, terrain, congestion and the device all affect the connection.
Lower-frequency bands generally travel farther and enter buildings more easily; higher bands can provide more capacity but are blocked more easily. A coverage map is a planning estimate, not a guarantee for a particular room, basement, train or crowded venue.
First try moving near a window, toggling airplane mode, restarting, checking network settings and testing outdoors. If multiple compatible phones have the same problem at the same address, report an area problem to the carrier before buying equipment yourself.
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An older mobile generation used for voice and low-speed data. Japanese carriers have retired or scheduled the retirement of their 3G services.
4G / LTE4G・LTE（第4世代移動通信）fō-jī / eru-tī-ī
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The mobile generation designed for higher capacity, lower latency and many connected devices, deployed with several frequency bands and network architectures.
5G SA / Standalone5G SA（スタンドアローン）faibu-jī esu-ē
A 5G architecture using a 5G core network rather than relying on a 4G core and 4G control connection as non-standalone 5G does.
ADSLADSLē-dī-esu-eru
An older broadband technology that sends data over a copper telephone line. Major Japanese consumer ADSL services have ended or are being retired.