  Provisioning of Quality of Service (QoS) is a key issue in any multi-media
system. However, in wireless systems, supporting QoS requirements of different
traffic types is more challenging due to the need to minimize two performance
metrics - the probability of dropping a handover call and the probability of
blocking a new call. Since QoS requirements are not as stringent for
non-real-time traffic types, as opposed to real-time traffic, more calls can be
accommodated by releasing some bandwidth from the already admitted
non-real-time traffic calls. If we require that such a released bandwidth to
accept a handover call ought to be larger than the bandwidth to accept a new
call, then the resulting probability of dropping a handover call will be
smaller than the probability of blocking a new call. In this paper we propose
an efficient Call Admission Control (CAC) that relies on adaptive multi-level
bandwidth-allocation scheme for non-real-time calls. The scheme allows
reduction of the call dropping probability along with increase of the bandwidth
utilization. The numerical results show that the proposed scheme is capable of
attaining negligible handover call dropping probability without sacrificing
bandwidth utilization.
