2.4 HCA

In HCA strategies the total set of channels is divided into two subsets. The first subset of channels is assigned to the cells of the system according to the FCA strategy. The second subset is kept in a central pool and assigned dynamically to the cells on demand to increase flexibility. Therefore, there are basically two types of CAS at the same time, FCA and DCA. When a new call arrives at a cell, the first attempt to serve it is by a nominal or fixed channel. If there is no free nominal channel, a channel from the dynamic set is assigned to the call. If this fails, then the call is blocked. The way in which the dynamic channels are managed follows any of the strategies in [32 61]. The ratio of fixed-to-dynamic channels is a significant parameter that defines the performance of the system in much the same manner that the ratio of nominal-to-borrowable channels defines the performance of a strategy with channel borrowing. In general, the ratio of fixed-to-dynamic channels is a function of the traffic load and would vary over time according to offered load distribution estimations [1].