Determining the Call Admission Region for Real -

The call admission problem for a wireless packet switched network supporting homogeneous applications-such as a cellular voice network-is an old one and has been extensively investigated in the past. The focus of the present article is to investigate the call admission region for a TDMA (wireless) system supporting heterogeneous real-time variable bit rate (VBR) applications with distinct quality of service (QoS) requirements and traac characteristics. The QoS is deened in terms of a maximum tolerable packet delay and dropping probability; packets may be dropped due to delay violations or channel induced errors. The call acceptance region is investigated in this article under the assumption that each user's per frame resource (slot) requests are communicated to the scheduler (resource allocation authority). The call acceptance region is shaped by the QoS that can be delivered by the up-link scheduling policy. In the beginning of this article, some mechanisms employed to inform the scheduler of the users' requests along with some scheduling policies are discussed. While theses scheduling policies identify QoS points in the call admission region, they cannot reveal the entire region. In this article, an approach is outlined on how to precisely determine the call admission region (largest set of QoS points delivered under any scheduling policy) for a TDMA system. This approach is shown to lead to the precise description of the reduced call admission region in the presence of channel errors. In order to demonstrate the performance improvement provided by a data link control (DLC) protocol, a simple QoS-sensitive DLC protocol operating over an erroneous channel is employed leading to an enlargement of the calculated call admission region. Finally, it is shown that feasible scheduling policies exist which do deliver at least the minimum QoS requirement of the applications whose associated QoS vector falls within the determined call admission region.