Capability based admission control for broadband CDMA networks

We study the admission control of heterogeneous traffic over the reverse link of broadband CDMA networks. With traffic heterogeneity, users can have diverse QoS requirements such as transmission rates, signal-to-interference ratio (SIR), and outage probability. On the other hand, individual users experience different levels of path loss and fading. All those factors should be considered while admitting a user. Our algorithm uses a concept called effective interference bandwidth to characterize the capability of a user to support user bandwidth demand. According to our previous work, the total bandwidth resource in a CDMA cell is divided into bandwidth available to user traffic for in-cell users, and interference bandwidth for other-cell interference. User effective interference bandwidth characterizes the maximal interference a user can tolerate, and is thus a limiting parameter of cell capacity. Basically, the cell capacity is approximately the total cell bandwidth minus the user effective interference bandwidth. Since the effective interference bandwidth term varies from user to user, each user imposes a different limit on the cell capacity. If a user with high effective interference bandwidth is admitted, it is possible that future users can be blocked, thus increasing the blocking probability. By requiring users with limited effective interference bandwidth, we optimize the overall blocking probability. In designing the admission algorithm, we first evaluate the expected average traffic in a cell. This value is used to compute the maximal allowable effective interference bandwidth. Then user effective interference bandwidth is compared with maximal allowable value for admission decision. Only users with interference bandwidth not exceeding the maximal allowable level are granted admission. Numerical results show that this scheme performs better than not checking user effective interference.