ADMISSION CONTROL SCHEME OF EXTENDED RTPS ALGORITHM FOR VOIP SERVICE IN IEEE 802.16E WITH ADAPTIVE MODULATION AND CODING

The extended real time polling service (ertPS) algorithm is added to IEEE 802.16e-2005 standards so that voice over internet protocol (VoIP) service could use resources efficiently by considering on/off characteristic of voice source. The IEEE 802.16e standard employs adaptive modulation and coding (AMC) to maximize transmission rate by assigning variable rate in accordance with the user's time-varying channel conditions determined mainly by distance from base station (BS) to mobile subscriber station (MSS). In order to apply AMC, we divide a cell into two zones with different average signal-to-noise ratio (SNR) where each zone uses its own one transmission mode. In this paper, we construct 3-dimensional Markov process of M/G/1 type whose steady state probability is obtained by the matrix analytic method. By using the steady state probability of Markov process, we obtain the probability distribution of queueing delay and find the admissible region of VoIP users with the required constraint on delay bound. Next, we propose a call admission control (CAC) scheme by considering two admissible regions for handoff calls and new calls satisfying constraints on delay bound and dropping probability of handoff call. In order to find dropping probability of handoff call and blocking probability of new call, we construct Markov chain model of proposed CAC scheme at call-level. By the mathematical results of packet-level and call-level, we obtain admissible region to admit new call and admissible region to admit handoff call satisfying the required constraints on delay bound and dropping probability of handoff call.