ght-chip Walsh code, the fundamental channel uses a four-chip Walsh code, and the supplemental channels use 2-bit Walsh codes to allow higher bit rates in favorable environments. Since the user terminal is sending fewer channels than the base station, the reverse link can use shorter Walsh codes to maintain orthogonality among its separate channels. The fundamental channel is used for voice calls and for low-bit-rate signaling during a data call, the same 9600-bit-per-second RS1 and 14.4-kbps RS2 as cdmaOne. Unlike cdmaOne, the power-control bits are in the pilot channel rather than inserted into the fundamental bit stream. Supplemental channels can be dedicated or shared, the same as in the forward di- rection. A single link can have only a fundamental channel, or it can have one or more supplemental channels along with a low-bit-rate fundamental channel. When a single reverse supplemental channel is shared among many user terminals, scheduling is 9The potential of higher data rates makes the extra capacity overhead of a pilot worthwhile. In cdmaOne, the highest reverse data rate is 14.4 kbps, which is not worth the extra overhead and design expense of a separate pilot. 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 handled by a medium access control (MAC) protocol. User terminals send MAC mes- sages across their own dedicated control channels and get confirmation before they use a shared supplemental packet data channel. The reverse cdma2000 link puts the pilot and control channels on its in-phase bits, puts the fundamental and supplemental channels on its quadrature bits, and balances them using a technique called complex spreading. cdma2000 uses orthogonal complex QPSK (OCQPSK), a technique to reduce out-of-band radio emissions. Because OCQPSK came out of international committees f