SM-based operators in the United States and elsewhere favor a standard based on the UMTS Universal Terrestrial Radio Access (UTRA) standard, which is more typically referred to as W-CDMA. W-CDMA has two proposed implementations: UMTS, which is based on FDD, and UMTS TDD/TD-CDMA, which is based on TDD. UMTS/W-CDMA operates in the frequency bands 1,920MHz to 1,980MHz and 2,110MHz to 2,170MHz, using FDD transmission. The minimum frequency band required is two 5MHz channels. The frequency reuse is N = 1, which means that all the frequencies can be reused in each cell, including adjacent cells. UMTS/ W-CDMA uses the modulation scheme QPSK and supports both circuit- and packet-based services. The maximum user data rate it supports is 1,920Kbps, but real-world experience at the moment is actually 384Kbps. The 3.5G enhancement Table 14.1 3G Standards Interface ITU Designation Technology Technique Carrier W-CDMA (UMTS, UTRA, W-CDMA Direct-sequence Single 5MHz FDD), IMT DS channel CDMA2000 (1X and 3X W-CDMA Multicarrier TDD Multicarrier RTT), IMT MC TD-SCDMA and UMTS W-CDMA DSSS (UMTS TDD), 1.6MHz or 5MHz TDD, IMT TC time code, TDD channels UWC-136/EDGE Single-carrier Single-carrier Chapter 14 Wireless WANs known as HSDPA (discussed later in this chapter) will offer data speeds up to 10Mbps, and with the addition of MIMO systems, 20Mbps may be possible. At the end of 2005, 146 W-CDMA licenses had been awarded in 48 countries, and there were 100 commercial W-CDMA networks operating in 42 countries, plus 4 more W-CDMA operators in precommercial stages (see the Global Mobile Suppliers Association, at www.gsacom.com). Also at the end of 2005, the total number of W-CDMA subscribers was over 40 million, and some 2 million new subscribers were being added monthly. In addition, there were 272 W-CDMA device models available on the market from 37 device suppliers, with 14 models supporting HSDPA. 3.5G Standards: The 3G Evolution The 3G evolution describes the seamless, compatible evolutionary path of enhance- ments to the existing G