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[ad_1] Image copyright Getty Images Image caption Internet connectivity through light waves could help 5G reach into buildings and underground The global race towards superfast "fifth generation" mobile internet, known as 5G, is entering a key phase. The trouble is no-one knows exactly which technologies will be best for offering such a service. But one telecoms firm may just have had a light-bulb moment. At its headquarters in Slough, O2 has installed an unusual demo. It's a room where a wireless internet connection is provided not through wi-fi, but li-fi - a system that transmits data through light waves rather than radio waves. The mobile operator thinks the system may help to offer 5G speeds in certain locations where getting coverage from an outdoor mobile signal is difficult. 'Li-fi 100 time...

[ad_1] Image copyright Getty Images/Reuters Image caption Despite claims to the contrary, President Trump is not directly involved with the test More than 200 million US mobile phones are set to receive a test "Presidential Alert" later on Wednesday. The trial is designed to check that a previously unused emergency communications system works properly. Unlike other alerts - such as natural disaster warnings - there is no way to opt out, except switching a device off or blocking its cellular connection. Some are describing the test as a "Trump Alert" - but the US president is not personally involved in the trial. Instead, the nationwide event is being run by the Federal Emergency Management Agency (Fema), which would also be in direct control of the system if a real alert was ordered by the US Pre...