Any use is subject to the Terms of Use as given at the website. Capacity Calculations for Cellular Networks 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. Source: CDMA CAPACITY AND QUALITY OPTIMIZATION Chapter Conventional Reuse Principles To distinguish code division multiple access (CDMA) from other modulation schemes, we call frequency division multiple access (FDMA) and time division multiple access (TDMA) schemes conventional reuse. 1 In these conventional reuse wireless systems, the modulation schemes are designed to be highly efficient of radio spectrum, designed to squeeze the most calls into a given frequency bandwidth. Once we have our efficient radio carriers, we make our conventional reuse systems efficient by managing interfer- ence as well as we can. 2 The effect of interference on cellular call quality is determined by the modulation scheme and by the radio environment, including radio path propa- gation and Rayleigh fading. 27.1 The AMPS Channel (FDMA) As we described in Chap. 6, the Advanced Mobile Phone System (AMPS) channel is a frequency division duplex (FDD) frequency modulation (FM) analog 30-kHz channel. It carries an audio signal from 300 to 3300 Hz. The AMPS system maintains the link with a supervisory audio tone (SAT) that can have one of three frequencies, 5970, 6000, or 6030 Hz, all out of the audio bandwidth. The AMPS receiver mutes the audio when it receives the wrong SAT or when no SAT is detected. When an interfering channel dominates the desired channel and that in- terfering channel has the same SAT frequency, the subscriber hears another call. We call this highly undesirable interference crosstalk. ¹We admit that this is our own term rather than an industry standard. We use it because it em- phasizes the unique nature of spread spectrum. 2The reader may wonder why a book on CDMA is spending so much time on