the FDD mode, probably the most common duplexing method, then separate forward and reverse carriers add up to 10 MHz. In time division duplex (TDD) mode, a single W-CDMA carrier serves both the forward and the reverse channels in 5 MHz of bandwidth. There are references to other W-CDMA bandwidths, 1.25, 10, and 20 MHz, but most of the lit- erature we have seen on W-CDMA refers only to the 5-MHz carrier width. Later versions of the W-CDMA standard include the multicarrier mode of cdma2000 described in Sec. 10.2.3 as part of the W-CDMA standard. 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 10.3.4 W-CDMA forward channel coding The chip rate for W-CDMA, in either FDD or TDD mode, is 3.84 Mchips per second. All channels in W-CDMA have pilot bits included at 1500 per second. By including pilot bits in each channel, we avoid having to use a separate pilot channel the way cdmaOne and cdma2000 do. In either case, the pilot is overhead-radio power dissipated into the CDMA carrier spectrum to lock its receiver onto a known signal that does not carry any subscriber data. The W-CDMA carrier supports up to 512 forward channels using orthagonal variable spreading factor (OVSF) to vary spreading gain. Voice channels use the longest codes, 512 bits, whereas higher-speed data channels use shorter codes down to 4 bits. Speech and data can be multiplexed onto a single channel with 1500 time slots per second. These are not TDMA time slots apportioned to separate channels but time slots to allow a single radio channel to offer multiple services to one subscriber. ¹³ Packet mode uses a shared channel, with TDMA over the radio link to multiplex to different users. The base station can send data to a variety of users by assigning dif- ferent time slots to different users. Both dedicated circuit and packet mo