Call Admission Control for Reducing Dropped Calls

Call admission control algorithms that reduce dropped calls in CDMA cellular sys-tems are discussed in this paper. The capacity of a CDMA system is conned by interference of users from both inside and outside of the target cell. Earlier algo-rithms for call admission control is based on the eective traÆc load for the target cell if one call is accepted. These algorithms ignore the interference eect of the to-be-accepted call on the neighboring cells. In our algorithms, the call admission decision is based on the eective traÆc loads for both the target cell and the neigh-boring cells. In addition, to prioritize hando calls, we also introduce the idea of soft guard channel, which reserves some traÆc load exclusively for hando calls. Stochastic reward net (SRN) models are constructed to compare the performance of the algorithms. The numerical results show that our algorithms can signicantly reduce the dropped calls with a price of increasing the blocked calls. To show the potential gain due to our algorithms, we introduce two new metrics: the increased blocking ratio for our algorithms and the increased dropping ratio for the conven-tional algorithms. From the numerical results, it is shown that our algorithms can reduce the dropped calls signicantly while the blocked calls are increased at a relatively small rate under both homogeneous and hot spot traÆc loads