criber, and voice/data mul- tiplexing over that channel. 14This is different from cdma2000, where the MAC messages are sent on a separate control channel. 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 Worldwide CDMA Standards subscribers are allowed to use shorter random times for retrying their attempts to im- prove their access to the shared channel. W-CDMA reverse channels use 3 to 1 convolutional coding for low rates and 2 to 1 turbo coding for high rates. For any required data rate, the system uses a spreading gain to expand the result to near 3.84 Mchips per second and then repeats some bits or punctures the bit stream to get the desired data rate to within 100 bits per second, the same as the forward direction. The reverse TDD mode uses data bursts of 2560 chips, 1500 per second, with a midamble, and the spreading gain can vary from 16 down to 1. The reverse W-CDMA link balances its in-phase and quadrature components with complex spreading using OCQPSK, also known as harmonized PSK, the same as cdma2000. 10.3.6 W-CDMA power control Open-loop power control is used to set initial reverse power levels. Closed-loop power control in W-CDMA, both forward and reverse, is sent 1500 times per second in the same cycle as the pilot. The inner loop adjusts the power to meet the Eb/No target, while the outer loop adjusts the E/No target based on BER. As in other CDMA tech- nologies, this dual loop is important because W-CDMA anticipates that some of its sub- scribers will be stationary while others are moving and will require a higher Eb/No to achieve the same BER performance. In TDD mode, the power control is slower, from 100 to 750 times per second, using a closed loop in the forward direction with the same inner and outer loops. The reverse uses only open-loop power control. We can get away with this because TDD uses 