TABLE OF CONTENTS In this chapter we present the code division multiple access (CDMA) equations for one server and for multiple servers and then discuss the assumptions held within the equations. We then apply the equations in general (to both directions) and specifically to the forward and reverse directions. This addresses many of the issues involved in moving the theoretical concept of CDMA into the practical world of cellular telephony. We close the chapter with a discussion of how the equations can be applied statistically to systems operating over time. Viewing a distribution over time allows us to address traffic engineering for the air interface.
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 necessary 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.
