Received power based call admission control techniques for UMTS uplink

Efficient call admission control (CAC) techniques are of paramount importance to achieve a flexible radio resources utilization with W-CDMA systems like UMTS. The number of calls that can be accepted in a cell depends on the interference conditions. The CAC scheme should be able to estimate if accepting a new call may affect the signal-to-interference ratio (SIR) of all the others. Practical CAC schemes proposed for the uplink direction, called received power based call admission control (RP-CAC), estimate the system load measuring the total power received at the base stations. Simple RP-CAC schemes just compare the measured power at the base station (BS) where the call is initiated with a threshold (single cell RP-CAC) or also measure the power received by neighboring BSs (multi cell RP-CAC). More complex RP-CAC schemes try also to estimate the load increase due to the new call (predictive RP-CAC). In this paper we compare the performance of these schemes and propose a new predictive RP-CAC scheme. We show that the advantage of using multi-cell strategy with respect to the single-cell one is negligible and that even the previously proposed predictive RP-CAC techniques cannot improve the performance in a remarkable way. On the contrary with our new scheme we increase the accepted traffic while keeping the call dropping probability very low.