lled the "carrier-to-crud ratio." Different modulation schemes have different S/N requirements. AM modulation sounds pretty terrible with a 10-dB S/N ratio, whereas a 3-dB S/N ratio exceeds an FM receiver's capture ratio and sounds fine to a listener. The use of the signal affects the S/N requirement as well: A telephone conversation tolerates much higher noise levels than the analog satellite feeds they used to use to transmit National Public Radio sym- phony orchestra broadcasts from the concert hall to the radio station. The natures of the signal and the interference also change the S/N requirement. Ana- log cellular FM signals have a 1-dB capture ratio and sound fine with a 3-dB S/N ratio so long as nobody is moving. However, since cellular is specifically a mobile telephone technology, it behooves us to have a performance specification robust enough to ensure 8We see no reason why they could not have added 14 dB on either side of the 100-dB range they were trying to cover and left the units at 1 dB each. Now, three decades later, cellular engineers learn about 0.78125 dB RSSI units. But those decisions were made a long time ago. 9This is another study one of us (Rosenberg) did. There is a very nice and interesting mathe- matical model of power control that takes into account communication errors in power control commands. The additional effect on power control when the measurement errors were taken into effect and found to be quite significant. 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. Radio Signal Quality Radio Signal Quality high signal quality for a moving radio source, as discussed in Sec. 2.1.4. It takes an- other 20 dB of S/I protection, more or less, to overcome the handicap of motion. 2.3.2 Digital: Bit error rate Rather than boast about a bit accuracy rate of 99.9999 percent, we describe digital link performance in terms 