UMTS provides several different terrestrial air interfaces, called UMTS Terrestrial Radio Access (UTRA).[4] All air interface options are part of ITU's IMT-2000. In the currently most popular variant for cellular mobile telephones, W-CDMA (IMT Direct Spread) is used.
Please note that the terms W-CDMA, TD-CDMA and TD-SCDMA are misleading. While they suggest covering just a channel access method (namely a variant of CDMA), they are actually the common names for the whole air interface standards.[5]
Non-terrestrial radio access networks are currently under research.
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