e for this 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. Radio Signal Quality Key Radio Concepts from a particular phone is greater at an antenna other than the antenna currently car- rying the call. In analog cellular development, power was measured in received signal strength in- dicator (RSSI) units, 0.78125 dB. Our understanding is that somebody told somebody that we needed to cover 100 dB of range, a reasonable interval. Having 7 bits available, somebody decided to divide the 100-dB range into 128 RSSI units with each unit being, therefore, 0.78125 dB. 8 Our mathematical radio models usually assume nearly perfect response to perfect measurement. In the analog cellular world, we found that we were happy when our measurements were within a few decibels of the true value. In CDMA, we are trying to manage our power levels to within a few tenths of a decibel. CDMA systems access S/I ratios many times per second and adjust power up or down according to the S/I ratio measurement. This measurement can be wrong, too, and the effect on CDMA power control of these measurement errors is significant. 9 The effect of these errors on CDMA capacity is discussed later in Secs. 8.5 and 27.6. 2.3 Signal Quality Measurement The two basic measures of radio signal quality are the signal-to-noise (S/N) ratio for analog and bit error rate (BER) for digital. While neither is a perfect measure of radio signal quality, both are excellent performance specifications. 2.3.1 Analog: The signal-to-noise ratio Whatever the analog signal being sent, it will almost certainly sound better with less competition for the receiver's attention. This competition can be internal noise (N), or it can be interference (I) in the radio environment. The signal-to-whatever ratio is ex- pressed as S/N or S/I or even S/(I + N). In more casual conversation, we have heard it ca