of how the equations can be applied statistically to sys- tems operating over time. Viewing a distribution over time allows us to address traffic engineering for the air interface. The CDMA Equations The CDMA equations allow us to calculate the theoretical capacity of one server or of a system that offers a multiserver environment. As you will see, one clear result of these equations is that the limit of CDMA capacity is quite pronounced. The number of users on a cell sector can increase steadily to a point without requiring a great deal more power from the base station and the user terminal. At some point, the power nec- essary to achieve a good call goes up very rapidly. And beyond a certain point, no amount of power in the world will serve all the users with high call quality. This result derived from the CDMA equations has a practical consequence: We can design CDMA systems that set a capacity limit by refusing all calls that require a power level higher than a predetermined setting. 28.1.1 One server Let a be the maximum interference to signal (I/S) ratio our CDMA channel can allow. The value of a is the spreading gain divided by the required Eb/No for the CDMA chan- nel. It is the job of the CDMA system and user terminal working together to set power levels just high enough for sufficient Eb/No so that the received power ru for the user terminal U is determined by the received power rv for all the other users U # U and the 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. CDMA Principles for Multicellular Systems Capacity and Quality Principles noise level N. Equation (28.1) says that the total interference plus noise is a times the received signal for user U: (28.1) For a single antenna face serving users, this symmetric equation has a symmetric so- lution obtained by setting all their received power levels to the same value r. Equation