the same frequency for both directions, so the fast-fading characteristics will be exactly the same for forward and reverse radio paths. In FDD systems, the different frequencies for forward and reverse carriers make the Rayleigh fading characteristics different enough that separate power control is necessary. 10.3.7 W-CDMA cell identification Cell sectors are differentiated by 512 distinct scrambling codes rather than through the use of timing differences. The user terminal acquires the cell signal by a three-stage search: Every sector has a primary synchronization channel (SCH) with the same 256-chip Golay code transmitted 1500 times per second. (Golay codes are a set of PN codes with special correlation properties.) The user terminal locks onto the strongest primary SCH. The user terminal looks to the secondary SCH, synchronized with the primary SCH, for one of 16 groups of scrambling codes. Each of the 16 groups has 32 codes, and the user terminal tries these in sequence to find a match. This procedure is much faster than searching through 512 PN codes in sequence. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Worldwide CDMA Standards Standards for Cellular Systems Having distinct codes for each cell sector avoids any problem of timing errors due to radio propagation delays at the speed of light. 10.4 TD-SCDMA Time division synchronized CDMA (TD-SCDMA) is the newcomer among 3G CDMA standards, and it has a different approach. cdma2000 was built from North American cdmaOne, and W-CDMA was built from European GSM. As a result, they tended to re- inforce, rather than resolve, the economic competition and rivalry between their 2G predecessors. TD-SCDMA took a different approach. Although its network components are optimized as a GSM upgrade path, its air-interface standard appears to be an ef- fort to optimize capacity and flexibility using