sen- tially more spreading gain in the code division multiple access (CDMA) channel and usually results in a power reduction as a result. When the offered rate is slightly lower, 8550 bits per second on a 9600-bit-per-second channel, some of the bits are repeated. Because most of the bits are sent just once, there is no economy of power available. We end up wasting the extra data capacity. When the offered data rate is slightly higher, 980 kbps on a 921-kbps channel, then we can employ a trick known as puncturing, where we steal a fraction of the bits and use them for extra data. The 921-kbps stream is turned into a larger stream of FEC coded bits, and some of these bits are deliberately replaced with a coded version of the other 59 kbps, but with few enough changes so that the FEC algorithm is not broken. The receiver detects the extra bits and uses them, whereas its FEC is robust enough to recover the original bit stream being sent. This does require a lower BER and more CDMA channel power because the error correction is weakened by puncturing. The various flavors of block codes are beyond the scope of this book, but the reader may en- counter, for example, linear block codes, binary cyclic codes [also called cyclic redundancy check (CRC)], and Bose-Chadhusi-Hocquenghem (BCH) codes. 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. Quality of Service (QoS) Quality of Service (QoS) 17.5 Conclusion Defining quality makes the essential link between good engineering and good business. Over the last 30 years, manufacturing companies have moved to systems that measure and ensure quality all the way from raw materials to satisfied customers. Defining the quality of services, rather than that of manufactured products, is more challenging, and the transition is recent. However, with convergence and an increasingly mature, competitive market, implementa