What does it mean when HD is displayed next to a full mobile signal on a mobile phone?

HD is displayed at the top of the mobile phone screen, indicating that China Mobile VoLTE high-definition voice service is enabled. If you need to cancel, go to Settings-(More Connection Settings)-Mobile Network-HD Voice-Turn off.

Note: VoLTE is Voice over LTE. It is an IP data transmission technology that does not require a 2G/3G network. All services are carried on the 4G network, which can realize the unification of data and voice services under the same network. . In other words, 4G networks not only provide high-speed data services, but also provide high-quality audio and video calls, and the latter requires VoLTE technology.