A Practical Method for Estimating Performance Metrics of Call Admission Control Schemes in Wireless Mobile Networks Emre A. Yavuz and Victor C. M. Leung Department of Electrical and Computer Engineering The University of British Columbia Vancouver, BC, Canada V6T 1Z4 Email: {emrey, vleung} @ece.ubc.ca Abstract — Providing the desired call blocking probability to not only new but also existing calls has been a challenge for wireless mobile network service providers. To satisfy different requirements for new and handoff call blocking probabilities, several call admission control (CAC) schemes have been proposed in the literature. Exact analysis of these schemes using two dimensional Markov chain is computationally intensive. Therefore under specific assumptions computationally efficient methods to analyze these systems using one dimensional Markov chain models have been considered. The “traditional” approach assumes that channel holding time for new and handoff calls have equal mean values. While the “normalized” approach relaxes this assumption, it is accurate only for the new call bounding CAC scheme. In this paper, we reevaluate the analytical methods for computing call blocking probabilities for several widely known call admission control schemes under more general assumptions by providing an easy to implement method. The numerical results show that when the average values of channel holding times for new and handoff calls are different, the proposed approach gives more accurate results when compared with the traditional and normalized methods based on one dimensional Markov chain modeling, while keeping the computational complexity low. Keywords - call admission control (CAC); call blocking probability; computational complexity; performance evaluation; priority based CAC schemes; quality of service (QoS); resource allocation; wireless mobile networks I. INTRODUCTION As the demand to support non-voice and multimedia services increases, radio resource management to satisfy diverse quality of service (QoS) requirements becomes increasingly important. To guarantee acceptable QoS in multi-service mobile environments, network planners need to consider certain constraints that provide upper limits for the blocking probability of different service or call types. Many call admission control (CAC) schemes have been proposed to enable the network to provide the desired QoS requirements by limiting the number of admitted calls to that network in order to reduce congestion and avoid call dropping. In wireless networks, other aspects of CAC need to be considered due to user mobility. An accepted call may be dropped before it is terminated as a result of the mobile user moving from its current cell to another, during a handoff, if the cellular network is unable to assign a new channel to the call in the new cell to continue its service due to lack of resources. Since dropping an on-going call is generally more objectionable to a mobile user than blocking a new call request, a higher priority is normally assigned for handoff calls over the new calls in order to minimize the call dropping probability. On the other hand, reducing handoff call blocking by channel reservation or other means could increase blocking for new calls. There is therefore a trade off between these two QoS measures [1]. The problem of maintaining the service continuity and QoS guarantees to the multimedia applications during handoffs is exacerbated by the increasing use of microcells and picocells in contemporary wireless networks. CAC for highspeed networks and wireless networks has been intensively studied in the past [2] and many handoff priority-based CAC schemes have been proposed [1], [3]–[8]. These can be classified into two broad categories: 1) Guard Channel (GC) Schemes: A set of guard channels are reserved for handoff calls. There are four different schemes. (a) The cutoff priority scheme blocks a new call if the number of free channels is less than the number of guard channels reserved for handoff calls [3][7][8]. (b) The fractional guard channel scheme admits a new call with certain probability that depends on the number of busy channels in the cell. It is first proposed by Ramjee et al. [1]. (c) The new call bounding scheme limits the number of new calls admitted to the cell to some number less than the total number of available channels. (d) The rigid division-based scheme divides all channels available in a cell into two groups: one for common use and the other only for handoff calls [9]. 2) Queuing Priority (QP) Schemes: Calls are accepted whenever there are free channels; otherwise they are queued with certain rearrangements in the queue. Although various combinations of the above schemes are possible, we concentrate only on GC schemes as we limit our discussion to the problems of call acceptance and dropping.