Bandwidth and Delay Guaranteed Call Admission Control Scheme for QOS Provisioning in IEEE 802.16e Mobile WiMAX Kalikivayi Suresh and Iti Saha Misra Electronics and Telecommunication Engineering Jadavpur University Kolkata, India suresh_juece@yahoo.co.in;itimisra@cal.vsnl.net.in Kalpana saha (Roy) Computer Science & Engineering Govt. College of. Engg. & Ceramic Technology, Kolkata Kolkata, India klpnsh@yahoo.com Abstract— An efficient Call Admission Control (CAC) scheme for IEEE 802.16e Mobile WiMAX that satisfies both bandwidth and delay guarantee to the admitted connections has been proposed in this paper. The proposed CAC scheme provides higher priority to Handoff connections, because it is more annoying to drop an ongoing connection than blocking a newly originated connection. Also UGS connections are given higher priority because UGS is the most common service used by the people for communication in everyday life. An analytical model is developed to evaluate the performance of the CAC scheme. The proposed CAC scheme is compared with two other existing CAC schemes proposed in literatures. Numerical results show that the proposed CAC scheme could be the better choice for admission control in terms of blocking and dropping probabilities of the connections and bandwidth utilization of the system. Key words: Call Admission Control, Delay Guarantee, IEEE 802.16e, Mobile WiMAX, QoS. I. INTRODUCTION Broadband wireless access (BWA) technology based on the IEEE 802.16 [1, 2] family of standards delivers high data rate over long distance. IEEE 802.16 families of standards also provide Quality of Service (QoS) guarantees to different types of services. Five different types of services are defined for Mobile WiMAX. They are Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), extended real-time Polling Service (ertPS), non real-time Polling Service (nrtPS) and Best Effort Service (BE). The QoS parameters specified in the standard are Maximum Sustained Traffic Rate (MSTR), Minimum Reserved Traffic Rate (MRTR), Maximum Latency (ML), Tolerated Jitter (TJ), and Request/Transmission Policy. Although IEEE 802.16 standards defined the QoS parameters, they did not specify how these QoS parameters are satisfied and is an open issue. Only Request/Transmission policy is defined in the standard. CAC plays an important role in QoS provisioning for IEEE 802.16 networks. The MAC of IEEE 802.16 is connection- oriented; therefore the Mobile Stations (MSs) should establish an end-to-end connection with the BS, before actually transmitting the data. For this the MS should send a request with the required QoS parameters for connection admission, to the Base Station (BS). The BS upon receiving the request will check whether it can provide the required QoS for that connection, if the request was accepted and at the same time verifies whether the QoS of all the ongoing connections can be maintained. Based on this it will take a decision on whether to accept or reject the connection. The process described above is called as CAC mechanism. The most important concern for providing CAC in IEEE 802.16 networks is to guarantee QoS of different types of connections and at the same time decreasing the Connection Blocking Probability (CBP), the Connection Dropping Probability (CDP) and to optimize the Bandwidth Utilization (BU). In [3] the authors proposed a dynamic CAC scheme for IEEE 802.16d Fixed WiMAX. The proposed CAC scheme uses bandwidth reservation and degradation policies. Bandwidth reservation policy is used to prioritize the UGS connections. Degradation is the method of decreasing the bandwidth allocated to the admitted connections in order to accommodate more number of connections. Two QoS parameters MSTR and MRTR specified in the standard allow us to degrade the bandwidth. Initially when there is few numbers of connections in the network, the connections are given maximum amount of bandwidth (Which is equal to the MSTR). As the number of connections admitted into the network increases the bandwidth allocated to the connections is decreased to the minimum required level (which is equal to MRTR). MSTR and MRTR QoS parameters are defined only for rtPS and nrtPS services. So degradation is only possible on rtPS and nrtPS connections. In this CAC scheme only nrtPS connections are degraded. In this paper authors shows that degradation model improves the bandwidth utilization of the system as well as decreases the blocking probabilities of the service flows than that of the constant rate CAC scheme. But this scheme does not provide any delay guarantees to the admitted connections and also does not support mobility and therefore it is not directly applicable to Mobile WiMAX. In [4] Liping Wang et al. proposed a CAC scheme (CAC- 2) based on the IEEE 802.16e. In that Handoff connections are given higher priority, than newly originated connections using guard channel scheme, which might result in wastage of bandwidth. The authors also used degradation mechanism for giving priorities among different types of services as well as to increase the performance of the system. In [5] Yin Ge and Geng-Sheng (G.S.) Kuo pro-posed a CAC (CAC-3) scheme for IEEE 802.16e Mobile WiMAX. In that the authors gave This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE "GLOBECOM" 2008 proceedings. 978-1-4244-2324-8/08/$25.00 © 2008 IEEE.