Universal Mobile Telecommunications System (UMTS) is an evolution of GSM and GPRS. The air interface has been changed from a Time Division Multiple Access (TDMA) based system to a Wideband Code Division Multiple Access (W-CDMA) based air interface. This change was required to achieve the data rate of 2 Mbps to the mobile which is a 3G requirement. This course provides the details of the UMTS W-CDMA air interface, known as UMTS Terrestrial Radio Access (UTRA). The W-CDMA physical layer is key to achieving higher data rates and supporting new features. This course provides an overview of the physical layer. In addition, power control and soft handover, important features of any CDMA air interface, are discussed. The UMTS defined radio interface includes a number of channels, which are presented with an explanation of their usage. The course concludes with a discussion on how the high data rates and multiple simultaneous services are delivered using UMTS.