Overview

In CDMA systems, the number of simultaneous users occupying resources should be limited so that an appropriate level of communication quality can be maintained. In this aspect, CAC plays a very important role in CDMA systems because it directly controls the number of users. CAC schemes are usually based on a threshold mechanism whose purpose is to ensure that the performance of users in the system satisfies their specified QoSs. In particular, CACs for the CDMA system can be classified into two schemes: interference-based CAC (ICAC) and number-based CAC (NCAC) ^[1]. The NCAC admits a new connection if total number of existing connections in the system is less than a predefined value, while the ICAC admits a new connection if total interference in the system is less than a certain threshold. As a reference to such thresholds for CAC in CDMA systems, one of the capacity bounds explained in previous sections can be utilized.

In practice, however, even if a fixed frequency band is used in a cell, the capacity bounds may vary with the loading of home and neighboring cells, mainly because co-channel interference changes according to the loading. For the design of robust and stable CAC schemes, it is important to consider the effect of the disturbance of system parameters on the threshold for CAC schemes, which directly corresponds to the effect of disturbance of the capacity parameters on the system capacity.

A typical way to quantitatively describe the change in the system capacity due to...